EQUITY OFFICE PROPERTIES TRUST
S-4, 2000-04-26
REAL ESTATE INVESTMENT TRUSTS
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<PAGE>   1

     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON APRIL 26, 2000
                                                     REGISTRATION NO. 333-
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                         ------------------------------

                                    FORM S-4
                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933
                         ------------------------------

<TABLE>
<S>                                                   <C>
           EQUITY OFFICE PROPERTIES TRUST
         EOP OPERATING LIMITED PARTNERSHIP                        CORNERSTONE PROPERTIES INC.
   (Exact name of registrant as specified in its         (Exact name of registrant as specified in its
               governing instrument)                                 governing instrument)
</TABLE>
<TABLE>
<S>                    <C>                     <C>                  <C>                    <C>
      MARYLAND                  6798               36-4151656
      DELAWARE                  6798               36-4156801              NEVADA                   6798
      (State of        (Primary SIC Code No.)   (I.R.S. Employer          (State of        (Primary SIC Code No.)
     Organization)                             Identification No.)      Organization)

<S>                    <C>
      MARYLAND
      DELAWARE             74-2170858
      (State of         (I.R.S. Employer
     Organization)     Identification No.)
</TABLE>

<TABLE>
<S>                                                   <C>
       TWO NORTH RIVERSIDE PLAZA, SUITE 2100                     TOWER 56, 126 EAST 56TH STREET
              CHICAGO, ILLINOIS 60606                               NEW YORK, NEW YORK 10022
                   (312) 466-3300                                        (212) 605-7100
(Address, including zip code, and telephone number,   (Address, including zip code, and telephone number,
   including area code, of registrants' principal        including area code, of registrant's principal
                 executive offices)                                    executive offices)
           ------------------------------                        ------------------------------
              STANLEY M. STEVENS, ESQ.                                   JOHN S. MOODY
  EXECUTIVE VICE PRESIDENT AND CHIEF LEGAL COUNSEL                  CHIEF EXECUTIVE OFFICER
       TWO NORTH RIVERSIDE PLAZA, SUITE 2100                     TOWER 56, 26 EAST 56TH STREET
              CHICAGO, ILLINOIS 60606                               NEW YORK, NEW YORK 10022
                   (312) 466-3300                                        (212) 605-7100
 (Name, address, including zip code, and telephone     (Name, address, including zip code, and telephone
 number, including area code, of agent for service)    number, including area code, of agent for service)
           ------------------------------                        ------------------------------
                     COPIES TO:                                            COPIES TO:
            J. WARREN GORRELL, JR., ESQ.                             WILLIAM B. FRYER, ESQ.
              GEORGE P. BARSNESS, ESQ.                              JOHN J. KELLEY III, ESQ.
               HOGAN & HARTSON L.L.P.                                   KING & SPALDING
            555 THIRTEENTH STREET, N.W.                               191 PEACHTREE STREET
            WASHINGTON, D.C. 20004-1109                              ATLANTA, GA 30303-1763
                   (202) 637-5600                                        (404) 572-4600
</TABLE>

                         ------------------------------

    APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE OF THE SECURITIES TO THE
PUBLIC: As soon as practicable after the effective date of this Registration
Statement.

    If the securities being registered on this form are being offered in
connection with the formation of a holding company and there is compliance with
General Instruction G, check the following box.  [ ]

    If this Form is filed to register additional securities for an offering
pursuant to rule 462(b) under the Securities Act, check the following box and
list the Securities Act registration statement number of the earlier effective
registration statement for the same offering.  [ ]

    If this Form is a post-effective amendment filed pursuant to rule 462(d)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering.  [ ]
                         ------------------------------
                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------------------
- ---------------------------------------------------------------------------------------------------------------------------------
                                                                 PROPOSED MAXIMUM        PROPOSED MAXIMUM
        TITLE OF EACH CLASS OF              AMOUNT TO BE          OFFERING PRICE        AGGREGATE OFFERING         AMOUNT OF
      SECURITIES TO BE REGISTERED          REGISTERED (1)            PER UNIT                 PRICE            REGISTRATION FEE
- ---------------------------------------------------------------------------------------------------------------------------------
<S>                                      <C>                  <C>                     <C>                     <C>
Equity Office Properties Trust common
  shares of beneficial interest, $.01
  par value per share..................      13,467,154                N/A                     N/A               $61,329.42(2)
- ---------------------------------------------------------------------------------------------------------------------------------
EOP Operating Limited Partnership class
  A units of limited partnership
  interest.............................      13,467,154                N/A                     N/A               $61,329.42(2)
- ---------------------------------------------------------------------------------------------------------------------------------
Cornerstone Properties Inc. common
  stock, no par value..................     19,214,088(3)           $18.28125             $55,325,351.25         $14,605.89(4)
- ---------------------------------------------------------------------------------------------------------------------------------
- ---------------------------------------------------------------------------------------------------------------------------------
</TABLE>

(1) Represents the maximum number of common shares of beneficial interest of
    Equity Office Properties Trust, class A units of limited partnership
    interest in EOP Operating Limited Partnership and shares of common stock of
    Cornerstone Properties Inc., respectively, that may be issued pursuant to
    the transactions described herein. The class A units of limited partnership
    interest in EOP Operating Limited Partnership are redeemable on a one-
    for-one basis for common shares of Equity Office Properties Trust, or the
    cash equivalent thereof, at the election of Equity Office Properties Trust.

(2) The registration fee was paid previously by Equity Office Properties Trust
    (File No. 333-33600).

(3) 16,187,744 of such shares were registered previously by Cornerstone (File
    No. 333-72449). Cornerstone paid a filing fee of approximately $69,331.60
    for such shares.

(4) Pursuant to rule 457(f)(1) and 457(c) under the Securities Act of 1933, the
    registration fee has been calculated based on a price of $18.28125 per share
    of Cornerstone common stock, which equals the average of the high and low
    price per share of Cornerstone common stock as reported on the New York
    Stock Exchange on April 19, 2000.
                         ------------------------------

    THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF
THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(a)
MAY DETERMINE.
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<PAGE>   2

   THE INFORMATION IN THIS CONSENT SOLICITATION/INFORMATION STATEMENT/PROSPECTUS
   IS NOT COMPLETE AND MAY BE CHANGED. WE MAY NOT SELL THESE SECURITIES UNTIL
   THE REGISTRATION STATEMENT FILED WITH THE SEC IS EFFECTIVE. THIS CONSENT
   SOLICITATION/INFORMATION STATEMENT/PROSPECTUS IS NOT AN OFFER TO SELL THESE
   SECURITIES AND IS NOT SOLICITING AN OFFER TO BUY THESE SECURITIES IN ANY
   JURISDICTION WHERE THE OFFER OR SALE IS NOT PERMITTED.

[EQUITY OFFICE LOGO]                                          [CORNERSTONE LOGO]

      PARTNERSHIP AND REIT MERGERS PROPOSED -- YOUR VOTE IS VERY IMPORTANT

    The board of trustees of Equity Office Properties Trust, the general partner
of EOP Operating Limited Partnership, and the board of directors of Cornerstone
Properties Inc., the general partner of Cornerstone Properties Limited
Partnership, have approved and adopted a merger agreement that provides for the
acquisition of Cornerstone by Equity Office and the acquisition of Cornerstone
Partnership by EOP Partnership.

APPROVAL OF THE MERGERS:

    EOP Partnership Unitholders.  We are furnishing this consent
solicitation/information statement/prospectus to EOP Partnership unitholders for
your information only. The partnership agreement of EOP Partnership requires the
approval of the REIT merger by the consent of unitholders holding at least a
majority of the outstanding EOP Partnership units, including any EOP Partnership
units held by Equity Office. Because Equity Office owns more than a majority of
the outstanding partnership units of EOP Partnership, no vote or consent of EOP
Partnership unitholders, other than Equity Office, is required for approval of
the REIT merger, and none is being solicited. Equity Office, as the general
partner of EOP Partnership, has already approved the merger of Cornerstone
Partnership with and into EOP Partnership. No other vote or consent of
unitholders of EOP Partnership is required under the partnership agreement of
EOP Partnership for approval of the partnership merger.

    CORNERSTONE PARTNERSHIP UNITHOLDERS.  WE ARE FURNISHING THIS CONSENT
SOLICITATION/INFORMATION STATEMENT/PROSPECTUS TO CORNERSTONE PARTNERSHIP
UNITHOLDERS IN ORDER FOR YOU TO APPROVE THE MERGER OF CORNERSTONE WITH AND INTO
EQUITY OFFICE AND THE MERGER OF CORNERSTONE PARTNERSHIP WITH AND INTO EOP
PARTNERSHIP BECAUSE THE PARTNERSHIP AGREEMENT GOVERNING CORNERSTONE PARTNERSHIP
REQUIRES THAT PARTNERS HOLDING A MAJORITY OF THE CORNERSTONE PARTNERSHIP UNITS
APPROVE EXTRAORDINARY TRANSACTIONS, SUCH AS THE MERGERS. ONLY HOLDERS OF RECORD
OF UNITS OF CORNERSTONE PARTNERSHIP ON      , 2000 WILL BE ELIGIBLE TO CONSENT
TO THE MERGER.

PARTNERSHIP MERGER CONSIDERATION TO BE RECEIVED BY CORNERSTONE PARTNERSHIP
UNITHOLDERS:

    In the partnership merger, each of your Cornerstone Partnership units will
be converted into .7009 of a partnership unit of EOP Partnership. Alternatively,
you may elect to redeem all or any portion of your Cornerstone Partnership units
immediately prior to the partnership merger for shares of Cornerstone common
stock, which would then enable you to participate in the REIT merger as a
stockholder of Cornerstone. Cornerstone stockholders may elect to receive for
each share of common stock either $18.00 in cash, without interest, or 0.7009 of
an Equity Office common share, subject to proration if the cash election is
oversubscribed or undersubscribed. You may elect to condition your redemption of
Cornerstone Partnership units upon the ability to receive in the REIT merger
only cash in exchange for all or any specified portion of the Cornerstone common
stock issued in the redemption.

    AFTER CAREFUL CONSIDERATION, THE CORNERSTONE BOARD HAS DETERMINED THAT THE
PARTNERSHIP MERGER IS IN YOUR BEST INTERESTS AND IN THE BEST INTERESTS OF
CORNERSTONE STOCKHOLDERS, AND THE BOARD RECOMMENDS THAT YOU VOTE FOR APPROVAL OF
THE MERGERS.

    Cornerstone cannot complete the mergers unless they are approved by partners
of Cornerstone Partnership holding a majority of the Cornerstone Partnership
units, including Cornerstone, which must vote its Cornerstone Partnership units
in proportion to the manner in which all outstanding shares of capital stock of
Cornerstone are voted at the special meeting of stockholders of Cornerstone to
be held on     , 2000 in connection with the REIT merger.

    This document provides you with detailed information about the consent
solicitation and the proposed mergers, including instructions on how to redeem
your units for shares of Cornerstone common stock prior to the partnership
merger and how to elect to receive Equity Office common shares or cash if you
choose to redeem all or any portion of your units and participate in the REIT
merger as a stockholder of Cornerstone. You also can get information from
publicly available documents filed by Cornerstone, Equity Office and EOP
Partnership with the SEC. WE ENCOURAGE YOU TO READ THIS ENTIRE DOCUMENT
CAREFULLY, INCLUDING THE SECTION ENTITLED "RISK FACTORS" ON PAGE          .

    Your Cornerstone Partnership consent form is due by          , 2000. Your
notice of redemption form of election is due at least two days prior to the date
of the Cornerstone stockholder special meeting, which is currently scheduled to
occur on            , 2000. This document also constitutes the information
statement of EOP Partnership, the prospectus of Cornerstone with respect to the
shares of common stock of Cornerstone issued in exchange for units of limited
partnership of Cornerstone Partnership prior to the partnership merger and the
prospectus of EOP Partnership and Equity Office with respect to the units of
limited partnership interest of EOP Partnership to be issued in exchange for
Cornerstone Partnership units in the partnership merger and the Equity Office
common shares thereafter issuable upon redemption of the EOP Partnership units
issued in the partnership merger, respectively.
                            EACH VOTE IS IMPORTANT.
              PLEASE COMPLETE, SIGN, DATE AND RETURN YOUR CONSENT.

Neither the SEC nor any state securities commission has approved or disapproved
of the securities to be issued in connection with the partnership merger or
passed upon the adequacy or accuracy of this consent solicitation/information
statement/prospectus. Any representation to the contrary is a criminal offense.

THE ATTORNEY GENERAL OF THE STATE OF NEW YORK HAS NOT PASSED ON OR ENDORSED THE
MERITS OF THIS OFFERING. ANY REPRESENTATION TO THE CONTRARY IS UNLAWFUL.

 This consent solicitation/information statement/prospectus is dated          ,
                                      2000
           and it is first being mailed on or about          , 2000.
<PAGE>   3

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                       PAGE
                                       ----
<S>                                    <C>
SUMMARY..............................     1
  The Companies and the
     Partnerships....................     1
  Information About the Actions Taken
     or to be Taken by the General
     Partner of EOP Partnership......     1
  Cornerstone Partnership
     Unitholders' Consent
     Procedures......................     2
  Cornerstone Voting Agreements......     2
  Approval of the REIT Merger by
     Equity Office Common
     Shareholders and Cornerstone
     Common and Preferred
     Stockholders....................     2
  Recommendation of the Cornerstone
     Board...........................     2
  The Partnership Merger.............     3
     Conditions to the Partnership
       Merger and the REIT Merger....     3
     Termination of the Merger
       Agreement; Termination Fees...     3
     Summary of Material Federal
       Income Tax Consequences.......     4
  Accounting Treatment...............     4
  Conflicts of Interest of
     Cornerstone Directors and
     Officers in the   Mergers.......     5
  Trustees of Equity Office Following
     the REIT Merger.................     5
  Differences in the Rights of
     Unitholders and Shareholders....     5
  Partnership Merger Selected
     Historical Consolidated
     Financial Data..................     6
     EOP Partnership.................     6
     Cornerstone Partnership.........     9
     Equivalent Per Unit Data........     9
     Prices of EOP Partnership Units
       and Cornerstone Partnership
       Units.........................    10
  Partnership Merger Summary
     Unaudited Pro Forma Condensed
     Combined Financial Data.........    12
  REIT Merger Selected Historical
     Consolidated Financial Data.....    14
     Equity Office...................    14
     Cornerstone.....................    16
     Equivalent Per Share Data.......    17
     Market Prices of Equity Office
       Common Shares and Cornerstone
       Common Stock..................    18
  REIT Merger Selected Unaudited Pro
     Forma Condensed Combined
     Financial Data..................    19
RISK FACTORS.........................    21
A WARNING ABOUT FORWARD-LOOKING
  STATEMENTS.........................    26
</TABLE>

<TABLE>
<CAPTION>
                                       PAGE
                                       ----
<S>                                    <C>
INFORMATION ABOUT THE ACTIONS TAKEN
  OR TO BE TAKEN BY THE GENERAL
  PARTNER OF EOP PARTNERSHIP.........    26
CORNERSTONE PARTNERSHIP CONSENT
  SOLICITATION.......................    27
  Purpose of the Consent
     Solicitation....................    27
  Who Can Consent....................    27
  Consent, Redemption and Election
     Procedures......................    27
  Required Vote......................    28
  How You May Revoke Your Notice of
     Redemption......................    29
  How You May Revoke Your Consent or
     Form of Election................    29
  Cost of This Consent
     Solicitation....................    29
THE PARTNERSHIP MERGER...............    30
  Structure of the Mergers;
     Partnership Merger Exchange
     Ratio...........................    30
  Redemption of Cornerstone
     Partnership Units; Participation
     in Cash/Share Election..........    30
  Background of the Partnership
     Merger and the REIT Merger......    30
  Equity Office's Reasons for the
     Mergers.........................    34
  Opinion of Equity Office's
     Financial Advisor...............    35
  Cornerstone's Reasons for the
     Mergers.........................    40
  Opinion of Cornerstone's Financial
     Advisor.........................    42
  Interests of Cornerstone's
     Directors and Officers in the
     Mergers.........................    47
  Equity Office Board of Trustees and
     Executive Officers after the
     Mergers.........................    49
  Assumption of Cornerstone's
     Obligations Under Registration
     Rights Agreements...............    50
  Accounting Treatment...............    51
  Resales of EOP Partnership Units
     and Equity Office Common
     Shares..........................    51
  No Appraisal Rights................    52
THE MERGER AGREEMENT.................    52
  Closing; Effective Time of the
     Partnership Merger and the REIT
     Merger..........................    52
  The Partnership Merger.............    53
     Redemption Right under the
       Partnership Agreement of
       Cornerstone Partnership.......    53
     Conditional Unit Redemption
       Right under the Merger
       Agreement.....................    53
  The REIT Merger....................    53
</TABLE>

                                        i
<PAGE>   4

<TABLE>
<CAPTION>
                                       PAGE
                                       ----
<S>                                    <C>
     Oversubscription of Cash........    54
     Oversubscription of Shares......    54
     Undersubscription of Cash and
       Shares........................    55
  Treatment of Cornerstone Stock
     Options.........................    56
  Representations and Warranties of
     EOP Partnership and Cornerstone
     Partnership.....................    56
  Conduct of Business of Equity
     Office and EOP Partnership
     Pending the Mergers.............    57
  Conduct of Business of Cornerstone
     and Cornerstone Partnership
     Pending the Mergers.............    58
  Conditions to the Mergers..........    60
     Conditions to the Parties'
       Obligations to Effect the
       Mergers.......................    60
     Conditions to the Obligations of
       Equity Office and EOP
       Partnership to Effect the
       Mergers.......................    61
     Conditions to the Obligations of
       Cornerstone and Cornerstone
       Partnership to Effect the
       Mergers.......................    62
  Tax Related Undertakings of EOP
     Partnership.....................    63
     Deficit Restoration
       Obligations...................    63
     Debt Maintenance and Lock-up
       Agreements....................    64
  No Solicitation by Cornerstone or
     Cornerstone Partnership.........    65
  Termination of the Merger
     Agreement.......................    67
     Right to Terminate..............    67
     Effect of Termination...........    68
  Expenses; Termination Fee..........    68
  Waiver and Amendment of the Merger
     Agreement.......................    70
  Indemnification; Directors' and
     Officers' Insurance.............    70
  Voting Agreements..................    71
     Cornerstone Voting Agreements...    71
     Equity Office Voting
       Agreements....................    72
  Preferred Stock Option Agreement...    72
  Amendments to Equity Office's
     Declaration of Trust Relating to
     "Domestically-Controlled" REIT
     Status..........................    72
  Acquisition of WCP Services........    73
MATERIAL FEDERAL INCOME TAX
  CONSEQUENCES.......................    73
  Overview...........................    73
  Summary of the Material Federal
     Income Tax Consequences of the
     Partnership Merger..............    75
  Tax Status of EOP Partnership......    76
</TABLE>

<TABLE>
<CAPTION>
                                       PAGE
                                       ----
<S>                                    <C>
  Tax Status of Cornerstone
     Partnership.....................    78
  Tax Consequences of the Partnership
     Merger to Cornerstone
     Partnership Unitholders That
     Receive EOP Partnership Units...    78
  Effect of Subsequent Events........    86
  Tax Consequences of Ownership of
     EOP Partnership Units After the
     Partnership Merger..............    88
  Tax Consequences of the Redemption
     of Cornerstone Partnership Units
     for Cornerstone Common Stock....    95
  Tax Consequences of the REIT
     Merger..........................    97
BUSINESS OF CORNERSTONE
  PARTNERSHIP........................   102
  General............................   102
  Operations.........................   102
  Ownership and Management of
     Cornerstone Partnership
     Properties......................   102
  Tenants............................   107
  Recent Developments................   108
  Competition........................   108
  Mortgage Indebtedness..............   109
  Revolving Credit Facility..........   111
  Legal Proceedings..................   111
CORNERSTONE PARTNERSHIP MANAGEMENT'S
  DISCUSSION AND ANALYSIS OF
  FINANCIAL CONDITION AND RESULTS OF
  OPERATIONS.........................   112
  Results of Operations..............   112
     Property Results................   112
     Earnings in Joint Ventures......   113
     Interest and Other Income.......   113
     Interest Expense................   113
     General and Administrative
       Expenses......................   114
     Gain (Loss) on Sale of Real
       Estate Assets.................   114
     Minority Interest in Joint
       Ventures......................   114
  Liquidity and Capital Resources....   114
     Cash Flow.......................   114
     Year Ended December 31, 1999
       Compared to Year Ended
       December 31, 1998.............   114
     Equity Transactions.............   115
     Funds From Operations...........   117
     Mortgage Indebtedness...........   118
     Other Indebtedness..............   119
     Liquidity.......................   119
  Other Matters......................   119
     General.........................   119
     Concentration of Risk...........   120
     Recently Issued Accounting
       Standards.....................   120
     Year 2000 Compliance............   120
</TABLE>

                                       ii
<PAGE>   5

<TABLE>
<CAPTION>
                                       PAGE
                                       ----
<S>                                    <C>
     Development Project.............   121
  Subsequent Events..................   121
  Quantitative And Qualitative
     Disclosures About Market Risk...   122
SECURITY OWNERSHIP OF CERTAIN
  BENEFICIAL OWNERS AND MANAGEMENT OF
  CORNERSTONE AND CORNERSTONE
  PARTNERSHIP........................   122
CORNERSTONE PARTNERSHIP POLICIES WITH
  RESPECT TO CERTAIN ACTIVITIES......   125
DESCRIPTION OF EOP PARTNERSHIP CLASS
  A UNITS............................   126
  Capitalization.....................   126
  Issuance of Additional Partnership
     Interests.......................   126
  Capital Contributions..............   127
  Distributions......................   127
  Preemptive Rights..................   128
  Conversion; Redemption.............   128
  Management.........................   129
  Sale of Substantially All of the
     Partnership Assets..............   130
  Transfers..........................   130
  Amendment of Partnership
     Agreement.......................   131
  Meetings...........................   132
COMPARISON OF RIGHTS OF
  UNITHOLDERS........................   132
  Capitalization.....................   132
  Issuance of Additional Partnership
     Interests.......................   133
  Capital Contributions..............   134
  Distributions......................   134
  Preemptive Rights..................   136
  Conversion; Redemption.............   136
  Management.........................   139
  Sale of Substantially All of the
     Partnership Assets..............   139
  Indemnification....................   140
  Transfers..........................   142
  Amendment of Partnership
     Agreement.......................   143
  Meetings...........................   145
  Financial Statements and Reports...   146
COMPARISON OF RIGHTS OF
  SHAREHOLDERS.......................   146
  Authorized Shares..................   147
  Voting Rights......................   147
  Classification of the Board........   148
  Number of Trustees/Directors;
     Removal of Trustees/Directors;
     Vacancies.......................   148
  Limitation of Trustee/Director and
     Officer Liability...............   149
</TABLE>

<TABLE>
<CAPTION>
                                       PAGE
                                       ----
<S>                                    <C>
  Indemnification....................   149
  Duties of Trustees and Directors...   152
  Maryland Elective Provisions.......   152
  Call of Special Meetings of
     Shareholders....................   153
  Shareholder Action by Written
     Consent.........................   154
  Advance Notice Provisions for
     Shareholder Nominations and
     Shareholder New Business
     Proposals.......................   154
  Amendment of the Declaration of
     Trust and Articles of
     Incorporation...................   154
  Amendment of the Bylaws............   155
  Mergers, Consolidations and Sales
     of Assets.......................   156
  Dissolution of Equity Office or
     Cornerstone; Termination of REIT
     Status..........................   156
  Business Combinations with
     Interested Shareholders.........   157
  Control Share Acquisitions.........   157
  Other Constituencies...............   158
  Dissenters' Rights.................   158
  Distributions......................   159
  REIT Ownership Limitations.........   159
LEGAL MATTERS........................   161
EXPERTS..............................   162
WHERE YOU CAN FIND MORE
  INFORMATION........................   163
WHAT INFORMATION YOU SHOULD RELY
  ON.................................   165
INDEX TO FINANCIAL STATEMENTS........   F-1
  EOP Partnership Pro Forma Condensed
     Combined Financial Statements...   F-2
  Equity Office Pro Forma Condensed
     Combined Financial Statements...  F-10
  Cornerstone Partnership Historical
     Consolidated Financial
     Statements......................  F-20
  Cornerstone Partnership Historical
     Consolidated Financial Statement
     Schedule: Schedule III..........  F-47
Annex A -- Agreement and Plan of
  Merger.............................   A-1
Annex B -- Opinion of J.P. Morgan
  Securities, Inc....................   B-1
Annex C -- Opinion of Lazard Freres &
  Co. LLC............................   C-1
Annex D -- Amendments to Equity
  Office Declaration of Trust to be
  Effected as
  Part of the Merger.................   D-1
</TABLE>

                                       iii
<PAGE>   6

                QUESTIONS & ANSWERS ABOUT THE PARTNERSHIP MERGER

Q: WHY ARE EOP PARTNERSHIP AND CORNERSTONE PARTNERSHIP PROPOSING THE PARTNERSHIP
   MERGER?

A: Equity Office and EOP Partnership are acquiring Cornerstone and Cornerstone
   Partnership in a two-step transaction. The first step involves the merger of
   Cornerstone Partnership with and into EOP Partnership, which we refer to as
   the "partnership merger." Cornerstone is the sole general partner of, and
   holds approximately an 87.1% interest in, Cornerstone Partnership. Equity
   Office is the sole general partner of, and holds approximately an 88.2%
   interest in, EOP Partnership. The second step involves the merger of
   Cornerstone with and into Equity Office, which we refer to as the "REIT
   merger." The REIT merger will take place immediately after the partnership
   merger.

   Both Equity Office and Cornerstone believe that the mergers will provide the
   combined company with high quality office buildings in locations that are
   complementary to existing EOP Partnership geographic locations. In addition,
   by increasing the office space owned and operated by EOP Partnership by
   approximately 24% based on square footage, the mergers will solidify its
   position as the nation's largest publicly-controlled owner and operator of
   office properties. The mergers also are expected to enhance EOP Partnership's
   ability to offer its customers a full range of office space options, as well
   as provide EOP Partnership with a development pipeline of new office
   properties in a supply-constrained market. To review the background and
   reasons for the mergers in greater detail, see pages 30-35 and 40-42 of this
   document.

Q: WHAT WILL I RECEIVE IN THE PARTNERSHIP MERGER?

A:Cornerstone Partnership Unitholders.  Cornerstone Partnership unitholders will
  receive 0.7009 of a class A unit of EOP Partnership for each Cornerstone
  Partnership class A common unit that is issued and outstanding, and not
  redeemed, immediately before the partnership merger.

  EOP Partnership Unitholders.  Each EOP Partnership class A unit held by EOP
  Partnership unitholders will continue to represent one EOP Partnership class A
  unit after the partnership merger. Based on the number of EOP Partnership
  units and Cornerstone Partnership units outstanding as of the date of this
  document, we estimate that, upon completion of the partnership merger and
  assuming that all Cornerstone Partnership class A common units are exchanged
  for EOP Partnership class A units in the partnership merger, approximately
       % of the outstanding EOP Partnership units will be owned by current
  Cornerstone Partnership unitholders other than Cornerstone, approximately
       % will be owned by persons who are EOP Partnership unitholders before
  completion of the partnership merger, other than Equity Office, and
  approximately      % will be owned by Equity Office.

Q: WILL I HAVE THE RIGHT TO REDEEM THE EOP PARTNERSHIP CLASS A UNITS THAT I
   RECEIVE IN THE PARTNERSHIP MERGER?

A: Yes. Under the merger agreement, you will have the right to redeem the EOP
   Partnership class A units that you receive in the partnership merger at any
   time following the completion of the mergers in accordance with the EOP
   Partnership partnership agreement. Under the EOP Partnership partnership
   agreement, a class A unit of EOP Partnership is generally redeemable on a
   one-for-one basis for an Equity Office common share or its cash equivalent,
   at the election of Equity Office.

Q: WILL I BE ABLE TO REDEEM MY CORNERSTONE PARTNERSHIP UNITS BEFORE THE
   PARTNERSHIP MERGER?

A: Yes. The methods of redemption are as follows.

   Redemption Right under Partnership Agreement of Cornerstone Partnership

   You may exercise any unit redemption right that you currently have under the
   partnership agreement of Cornerstone Partnership at any time before the
   partnership merger. Any exercise by you of your unit redemption right under
   the partnership agreement of Cornerstone Partnership will not be conditioned
   on completion of the mergers. If you exercise your unit redemption right
   under the partnership agreement of Cornerstone Partnership, Cornerstone will
   elect to pay you shares of Cornerstone common stock on a one-for-one basis
   for the Cornerstone Partnership units

                                       iv
<PAGE>   7

   redeemed. For units that you redeem before the partnership merger, you would
   not receive units of EOP Partnership in the partnership merger, but instead
   would participate in the REIT merger on the same basis as other common
   stockholders of Cornerstone if you continue to own the Cornerstone common
   stock received in the redemption at the time of the REIT merger. Generally, a
   Cornerstone Partnership unit is redeemable commencing one year after the date
   it was first issued. Accordingly, if you received your Cornerstone
   Partnership units less than one year ago, you may not have a currently
   exercisable unit redemption right under the partnership agreement of
   Cornerstone Partnership.

   Conditional Unit Redemption Right under the Merger Agreement

   Under the merger agreement, you have the right to redeem all or any portion
   of your Cornerstone Partnership units for Cornerstone common stock on a
   one-for-one basis, whether or not you have a currently exercisable right to
   redeem your units under the partnership agreement of Cornerstone Partnership.
   The exercise by you of the unit redemption right under the merger agreement
   will be effective only if the partnership merger is completed. Under the
   merger agreement, you also may condition your redemption of units on the
   ability to receive in the REIT merger only cash for some or all of the
   Cornerstone common stock that you would receive upon redemption of your
   Cornerstone Partnership units.

Q: WHAT WILL I RECEIVE IN THE REIT MERGER IF I REDEEM MY CORNERSTONE PARTNERSHIP
   UNITS FOR CORNERSTONE COMMON STOCK BEFORE THE PARTNERSHIP MERGER?

A: In the REIT merger, Cornerstone common stockholders may elect to receive for
   some or all of their shares of Cornerstone common stock either $18.00 per
   share in cash, without interest, or 0.7009 of a common share, par value $.01
   per share, of Equity Office, subject to proration if either the cash election
   or the share election is oversubscribed.

   If you redeem some or all of your Cornerstone Partnership units for
   Cornerstone common stock under the provisions of the partnership agreement of
   Cornerstone Partnership, or you elect to redeem some or all of your
   Cornerstone Partnership units for Cornerstone common stock under the merger
   agreement but do not condition the redemption on receiving cash in the REIT
   merger for the Cornerstone common stock to be issued to you upon redemption,
   you will participate in the REIT merger on the same basis as any other
   Cornerstone common stockholder.

   If you condition your unit redemption under the merger agreement on the
   ability to receive only cash in the REIT merger for some or all of your
   Cornerstone Partnership units, your Cornerstone Partnership units will be
   redeemed only if the cash condition is met and you will receive in the REIT
   merger $18.00 in cash per share of Cornerstone common stock received by you
   in the redemption. The cash condition will not be met if there is an
   oversubscription of cash by all Cornerstone common stockholders, taking into
   account cash elections made by all redeeming Cornerstone Partnership
   unitholders. However, if there is an undersubscription of cash, taking into
   account cash elections made by all Cornerstone common stockholders, including
   Cornerstone Partnership unitholders who redeem their Cornerstone Partnership
   units before the partnership merger, but not including cash elections made by
   Cornerstone Partnership unitholders who conditioned their unit redemptions on
   the ability to receive only cash in the REIT merger, you may nevertheless
   have the opportunity to have your units redeemed for Cornerstone common stock
   and receive cash in the REIT merger if the cash consideration available after
   giving effect to cash elections made by the Cornerstone common stockholders
   is sufficient to meet your specified cash condition and your conditional cash
   redemption is chosen by lot from among other conditional cash redemptions
   that were not initially satisfied.

Q: HOW WILL PRORATION AFFECT ME IF I REDEEM MY CORNERSTONE PARTNERSHIP UNITS FOR
   CORNERSTONE COMMON STOCK?

A: Proration is intended to provide each Cornerstone common stockholder with an
   equal opportunity to receive, in accordance with such stockholder's election,
   the cash consideration and the Equity Office common share consideration that
   is available in the REIT merger.

                                        v
<PAGE>   8

   The aggregate REIT merger consideration to be paid to Cornerstone's common
   stockholders is fixed at approximately $1.054 billion in cash, or $18.00
   multiplied by 58,551,525 shares, and a total number of Equity Office common
   shares equal to 0.7009 of an Equity Office common share multiplied by the
   number of shares of Cornerstone common stock issued and outstanding
   immediately before the closing of the REIT merger in excess of 58,551,525
   shares. Accordingly, each Cornerstone common stockholder who makes a cash
   election or a share election may receive a prorated combination of cash and
   share consideration, if, based on the elections made by other Cornerstone
   common stockholders, including Cornerstone Partnership unitholders who redeem
   their Cornerstone Partnership units before the partnership merger, cash
   elections or share elections are received for more cash consideration or
   share consideration, as applicable, than is available as part of the
   aggregate REIT merger consideration.

    For example:

    Oversubscription of Cash

    - if cash elections are received in the REIT merger for more than 58,551,525
      shares of Cornerstone common stock and you have elected to redeem some or
      all of your Cornerstone Partnership units without condition, then you will
      receive in the REIT merger:

      -- 0.7009 of an Equity Office common share in exchange for each share of
         Cornerstone common stock for which you did not make a cash election;
         and

      -- a combination of cash and Equity Office common shares, on a
         proportionate basis, for each share of Cornerstone common stock for
         which you made a cash election, so that the aggregate number of shares
         of Cornerstone common stock converted into cash in the REIT merger
         equals 58,551,525 shares, with Equity Office common shares issued in
         exchange for the remainder of the shares of Cornerstone common stock
         converted in the REIT merger.

    If you condition the exercise of your unit redemption right under the merger
    agreement on the ability to receive only cash for some or all of the
    Cornerstone common stock that you would receive in the redemption, an
    oversubscription of cash will cause the cash condition not to be satisfied
    and you will receive EOP Partnership units in the partnership merger based
    on the 0.7009 exchange ratio for the units that were subject to the cash
    condition. However, if there is an undersubscription of cash, taking into
    account cash elections made by all Cornerstone common stockholders,
    including Cornerstone Partnership unitholders who redeem their Cornerstone
    Partnership units before the partnership merger, but not including cash
    elections made by Cornerstone Partnership unitholders who conditioned their
    unit redemptions on the ability to receive cash in the REIT merger, you may
    nevertheless have the opportunity to have your units redeemed for
    Cornerstone common stock and receive cash in the REIT merger if the cash
    consideration available after giving effect to cash elections made by the
    Cornerstone common stockholders is sufficient to meet your specified cash
    condition and your conditional cash redemption is chosen by lot from among
    other conditional cash redemptions that were not initially satisfied. For
    any units redeemed by you that were not subject to the cash election
    condition, you will receive cash or Equity Office common shares, as elected
    by you, subject to the proration provisions described above.

    Oversubscription of Shares

    - if share elections are received for more shares of Cornerstone common
      stock than the difference between (a) the number of shares of Cornerstone
      common stock issued and outstanding immediately before the REIT merger,
      taking into account shares of Cornerstone common stock issued to
      Cornerstone Partnership unitholders who exercise their unit redemption
      rights, and (b) the 58,551,525 shares to be converted into cash in the
      REIT merger, and you have elected to redeem some or all of your
      Cornerstone Partnership units, then you will receive in the REIT merger:

      -- $18.00 in cash, without interest, in exchange for each share of
         Cornerstone common stock for which you did not make a share election;
         and

                                       vi
<PAGE>   9

      -- a combination of cash and Equity Office common shares, on a
         proportionate basis, for each share of Cornerstone common stock for
         which you make a share election, so that the aggregate number of shares
         of Cornerstone common stock converted into cash in the REIT merger
         equals 58,551,525 shares, with Equity Office common shares issued for
         the remainder of the shares of Cornerstone common stock converted in
         the REIT merger.

    If there is an oversubscription of Equity Office common shares, the cash
    condition to any conditional redemption will be met because cash will be
    available for each share of Cornerstone common stock for which cash was
    elected.

    Undersubscription of Cash and Shares

    - if cash elections are received for less than 58,551,525 shares of
      Cornerstone common stock AND share elections are received for less than
      the maximum number of shares of Cornerstone common stock to be converted
      into Equity Office common shares in the REIT merger, and you have elected
      to redeem some or all of your Cornerstone Partnership units, then you will
      receive in the REIT merger:

      -- $18.00 in cash, without interest, in exchange for each share of
         Cornerstone common stock for which you made a cash election;

      -- 0.7009 of an Equity Office common share in exchange for each share of
         Cornerstone common stock for which you made a share election; and

      -- a combination of cash and Equity Office common shares, on a
         proportionate basis, for each share of Cornerstone common stock for
         which you made neither a cash election nor a share election, so that
         the aggregate number of shares of Cornerstone common stock converted
         into $18.00 in cash, without interest, in the REIT merger equals
         58,551,525 shares, with Equity Office common shares based on the 0.7009
         exchange ratio issued for the remainder of the shares of Cornerstone
         common stock converted in the REIT merger.

    If there is an undersubscription of cash and an undersubscription of Equity
    Office common shares, the cash condition to any conditional unit redemption
    will be met because cash will be available for each share of Cornerstone
    common stock for which cash was elected.

Q: HOW DO I ELECT TO REDEEM MY CORNERSTONE PARTNERSHIP UNITS AND ELECT THE TYPE
   OF CONSIDERATION I WOULD LIKE TO RECEIVE IN THE REIT MERGER?

A: In order to redeem your Cornerstone Partnership units and elect the form of
   consideration that you would like to receive in the REIT merger, you must
   complete and sign the notice of redemption/form of election included with
   this document and return it to Cornerstone Partnership, with copies to
   Cornerstone and the exchange agent, in accordance with the instructions in
   the notice of redemption/form of election. The properly completed notice of
   redemption/form of election must be received at least two days prior to the
   date of the Cornerstone stockholder special meeting, which is currently
   scheduled to occur on           , 2000.

Q: IS MY NOTICE OF REDEMPTION REVOCABLE?

A: If you conditionally elect to redeem your Cornerstone Partnership units under
   the merger agreement, you can revoke or amend your notice of redemption at
   any time before two days prior to the date of the Cornerstone stockholder
   special meeting, by submitting written notice to Cornerstone Partnership,
   with copies to Cornerstone and to the exchange agent, which must receive the
   notice at or before that time. A notice of redemption under the provisions of
   the merger agreement is conditioned on the completion of the partnership
   merger and, if you choose, can be conditioned on the ability to receive only
   cash for some or all of the shares of Cornerstone common stock that would be
   received in the redemption.

   A notice of redemption made under the provisions of the partnership agreement
   of Cornerstone Partnership is not revocable and may not be conditioned on
   completion of the partnership merger or the ability to receive cash in the
   REIT merger.

                                       vii
<PAGE>   10

Q: IF I ELECT TO REDEEM MY CORNERSTONE PARTNERSHIP UNITS FOR CORNERSTONE COMMON
   STOCK, IS MY ELECTION TO RECEIVE CASH OR EQUITY OFFICE COMMON SHARES IN THE
   REIT MERGER FOLLOWING A REDEMPTION OF MY CORNERSTONE PARTNERSHIP UNITS
   REVOCABLE?

A: Yes. You may change your cash or share election or revoke it at any time
   prior to the deadline for submitting your consent form, as such deadline may
   be extended from time to time, by submitting written notice to the exchange
   agent, with a copy to Cornerstone Partnership, which must receive the notice
   at or before that time.

Q: WHAT HAPPENS IF THE PRICE OF EQUITY OFFICE COMMON SHARES AND/OR CORNERSTONE
   COMMON STOCK CHANGES BEFORE THE CLOSING OF THE TRANSACTION?

A: No change will be made to the 0.7009 exchange ratio applicable to both the
   partnership merger or the REIT merger, or the $18.00 per share cash amount
   payable in the REIT merger. The exchange ratio is fixed. Because the market
   value of Equity Office common shares will fluctuate before and after the
   closing of the REIT merger, the value of any EOP Partnership units that you
   will receive in the partnership merger or any Equity Office common shares
   that you receive in the REIT merger, as applicable, will fluctuate as well,
   and may differ from the $18.00 per share cash amount payable in the REIT
   merger. You should obtain current market prices for Equity Office common
   shares and shares of Cornerstone common stock, to which the current values of
   EOP Partnership units and Cornerstone Partnership units, respectively,
   correspond.

Q: HOW WAS THE EXCHANGE RATIO DETERMINED?

A: The exchange ratio was determined as part of the overall negotiation between
   Equity Office and Cornerstone regarding the merger consideration, taking into
   account the other terms of the transaction, including the aggregate and per
   share amounts of merger consideration payable in cash.

Q: WILL ANY FRACTIONAL EOP PARTNERSHIP UNITS BE ISSUED IN THE PARTNERSHIP
   MERGER?

A: No. A Cornerstone Partnership unitholder who, based on the 0.7009 exchange
   ratio applicable to the partnership merger, would be entitled to receive a
   number of EOP Partnership units that is not a whole number, will receive a
   number of EOP Partnership units that is rounded to the nearest whole number.

Q: WILL ANY FRACTIONAL EQUITY OFFICE COMMON SHARES BE ISSUED IN THE REIT MERGER?

A: No. Cash will be paid instead of fractional shares. This cash will be in
   addition to the approximately $1.054 billion of cash required to be paid to
   holders of Cornerstone common stock as part of the REIT merger consideration,
   and will not be taken into account for purposes of any proration that is
   required.

Q: TO WHAT AM I BEING ASKED TO CONSENT?

A: Cornerstone Partnership Unitholders. As a Cornerstone Partnership unitholder,
   you are being asked to approve by written consent the mergers, to the extent
   required under the partnership agreement of Cornerstone Partnership.

   EOP Partnership Unitholders.  This document is being sent to you for your
   information only. You are not being asked to approve the partnership merger,
   the REIT merger or the merger agreement.

Q: AS A CORNERSTONE PARTNERSHIP UNITHOLDER, DO I HAVE APPRAISAL RIGHTS?

A: No. Neither the Cornerstone Partnership partnership agreement nor the merger
   agreement provides you with appraisal rights and you have no such rights
   under Delaware law.

Q: WILL I RECOGNIZE GAIN OR LOSS AS A RESULT OF THE PARTNERSHIP MERGER?

A: The partnership merger generally is intended to qualify as a nonrecognition
   transaction for federal income tax purposes. However, if you experience a
   reduction in your share of partnership liabilities of Cornerstone Partnership
   when compared to your share of partnership liabilities of EOP Partnership,
   you will recognize taxable gain to the extent that the amount of that
   reduction in partnership liabilities exceeds your adjusted tax basis in the
   EOP Partnership units received immediately after the partnership merger. In
   addition, other circumstances present at the time of the partnership merger
   and subsequent events could cause you to recognize taxable gain as a result
   of the partnership merger.

                                      viii
<PAGE>   11

   The tax consequences of the partnership merger are very complicated and will
   vary for each Cornerstone Partnership unitholder according to its own
   circumstances. Therefore, it is important that you consult with your own tax
   advisor in order to determine the tax consequences to you of the partnership
   merger.

Q: IF I CURRENTLY HAVE A DEFICIT RESTORATION OBLIGATION WITH RESPECT TO MY
   CORNERSTONE PARTNERSHIP UNITS, WILL I HAVE THE RIGHT TO ENTER INTO A DEFICIT
   RESTORATION OBLIGATION WITH RESPECT TO THE EOP PARTNERSHIP UNITS THAT I
   RECEIVE IN THE PARTNERSHIP MERGER?

A: Yes. Under the merger agreement, EOP Partnership will allow each Cornerstone
   Partnership unitholder that has entered into a deficit restoration obligation
   with respect to its Cornerstone Partnership units as of the time of the
   partnership merger to enter into a deficit restoration obligation, in the
   same amount, with respect to the EOP Partnership units received in the
   partnership merger. The former Cornerstone Partnership unitholders as a group
   also will have the right to increase the aggregate amount of their deficit
   restoration obligations by a specified amount. In addition, under the merger
   agreement, EOP Partnership, in its sole discretion, may allow increases in
   the deficit restoration obligations of the former Cornerstone Partnership
   unitholders under limited circumstances after the partnership merger.
   Cornerstone Partnership unitholders who have entered into specific agreements
   with Cornerstone Partnership permitting them to enter into and increase
   existing deficit restoration obligations will continue to have these rights.

Q: WILL I RECOGNIZE TAXABLE GAIN OR LOSS AS A RESULT OF THE REDEMPTION OF MY
   CORNERSTONE PARTNERSHIP UNITS FOR CORNERSTONE COMMON STOCK IMMEDIATELY BEFORE
   THE PARTNERSHIP MERGER?

A: Yes. The redemption of Cornerstone Partnership units for Cornerstone common
   stock will be treated for federal income tax purposes as a fully-taxable sale
   of those units to Cornerstone in exchange for Cornerstone common stock. On
   the redemption of your Cornerstone Partnership units, you will recognize any
   gain or loss realized in an amount equal to the difference between the amount
   realized on the redemption and your adjusted tax basis in your Cornerstone
   Partnership units. If you have a "negative capital account" with respect to
   your Cornerstone Partnership units, the gain recognized on the redemption
   would exceed the value of the Cornerstone common stock received by the amount
   of that negative capital account.

   If you redeem your Cornerstone Partnership units for Cornerstone common stock
   immediately before the partnership merger you will have a basis in the
   Cornerstone common stock received in the redemption equal to the fair market
   value of that Cornerstone common stock at the time of the redemption. Your
   holding period in the Cornerstone common stock received will begin after the
   redemption.

   The tax consequences of a redemption will vary for each Cornerstone
   Partnership unitholder according to its own circumstances and, therefore, it
   is important that each Cornerstone Partnership unitholder consult with its
   own tax advisor in order to determine the tax consequences to it of a
   redemption.

Q: WILL I RECOGNIZE TAXABLE GAIN OR LOSS AS A RESULT OF THE REIT MERGER?

A: If you redeem your Cornerstone Partnership units before the partnership
   merger and participate in the REIT merger as a Cornerstone common
   stockholder, the following federal income tax consequences generally will
   result and will be in addition to any tax consequences that occur upon the
   redemption:

      - If you exchange Cornerstone common stock solely for Equity Office common
        shares in the REIT merger, you will not recognize gain or loss realized
        on the REIT merger for federal income tax purposes. However, you will
        recognize any taxable gain realized with respect to cash received for
        fractional shares;

      - If you receive solely cash in exchange for your Cornerstone common
        stock, you will recognize any taxable gain or loss realized for federal
        income tax purposes on the exchange of your Cornerstone common stock; or

      - If you receive both Equity Office common shares and cash, you will
        recognize any gain realized up to the amount of cash received, but you
        will not recognize any loss on the exchange.

                                       ix
<PAGE>   12

    The tax consequences to Cornerstone stockholders will depend on your
    personal situation. You should consult your tax advisor for a full
    understanding of the tax consequences of the REIT merger to you.

Q: WHAT WILL MY DISTRIBUTIONS BE AFTER THE PARTNERSHIP MERGER?

A: Until the partnership merger is completed, Cornerstone Partnership
   unitholders will continue to receive regular distributions in accordance with
   the partnership agreement of Cornerstone Partnership, including any
   distributions made in order to permit Cornerstone to pay to its stockholders
   immediately before the closing any dividends necessary to maintain
   Cornerstone's status as a real estate investment trust, or REIT. Cornerstone
   does not currently anticipate that it will pay any special pre-closing
   dividend. After the completion of the partnership merger, as an EOP
   Partnership unitholder, you will receive distributions in accordance with the
   EOP Partnership partnership agreement. EOP Partnership's current quarterly
   distributions are $0.42 per class A unit per quarter.

Q: IF I REDEEM MY CORNERSTONE PARTNERSHIP UNITS FOR CORNERSTONE COMMON STOCK AND
   PARTICIPATE IN THE REIT MERGER, WHAT WILL MY DIVIDENDS BE AFTER THE REIT
   MERGER?

A: After the completion of the REIT merger, if you receive Equity Office common
   shares in the REIT merger, you will receive the distributions payable to
   holders of Equity Office common shares with a record date after the closing.
   Equity Office's current quarterly distributions are $0.42 per share per
   quarter. If you do not receive any Equity Office common shares in the REIT
   merger, you will not receive dividends after the REIT merger is completed.

Q: WHAT SHOULD I DO NOW?

A: If you are a Cornerstone Partnership unitholder, you should indicate on your
   consent form whether or not you consent to the mergers and sign and mail it
   in the enclosed envelope as soon as possible. You also should send in your
   notice of redemption/form of election if you wish to redeem your Cornerstone
   Partnership units for Cornerstone common stock and participate in the REIT
   merger as a Cornerstone common stockholder.

   If you sign and send in your consent form and do not indicate if you consent,
   your consent will be assumed to have been given in favor of the proposal to
   approve the mergers.

Q: WHO CAN ANSWER MY QUESTIONS?

A: Cornerstone Partnership Unitholders. If you have more questions about the
   mergers, any redemption rights under the Cornerstone Partnership agreement or
   the merger agreement, or desire additional copies of this document, consent
   forms, or notice of redemption/forms of election, you should contact:

   Cornerstone Properties Limited Partnership
   c/o Cornerstone Properties Inc.
   Tower 56
   126 East 56th Street, 6th Floor
   New York, New York 10022
   Attention: Thomas P. Loftus
   Telephone: (212) 605-7100

   EOP Partnership Unitholders.  If you have more questions about the
   partnership merger or would like additional copies of this document, you
   should contact:

   EOP Operating Limited Partnership
   c/o Equity Office Properties Trust
   Two North Riverside Plaza,
   Suite 2100
   Chicago, Illinois 60606
   Attention: Diane Morefield
   Telephone: (312) 466-3286

                                        x
<PAGE>   13

                                    SUMMARY

     This summary highlights selected information from this consent
solicitation/information statement/prospectus. It may not contain all of the
detailed information that may be important to you. To understand the partnership
merger and the REIT merger fully and for a more complete description of the
legal terms of the mergers, you should read carefully this entire document and
the other documents to which we refer, including the merger agreement. For more
information about Equity Office, EOP Partnership and Cornerstone, see "Where You
Can Find More Information" on page 163. Each item in this summary refers to the
pages where that subject is discussed more fully.

THE COMPANIES AND THE PARTNERSHIPS

EQUITY OFFICE PROPERTIES TRUST
EOP OPERATING LIMITED PARTNERSHIP
Two North Riverside Plaza
Suite 2100
Chicago, Illinois 60606
(312) 466-3300

     Equity Office Properties Trust is the sole general partner of, and owns the
controlling interest in, EOP Operating Limited Partnership. Equity Office owns
all of its assets and conducts all of its operations through EOP Partnership,
which is engaged in acquiring, owning, operating and leasing office properties
and parking facilities. Equity Office is the nation's largest publicly held
owner and operator of office properties, with a portfolio of 294 office
buildings containing 77.0 million square feet in 23 states and the District of
Columbia. Equity Office, which has elected to be taxed as a real estate
investment trust, or REIT, for federal income tax purposes, is an independent
real estate company that manages all aspects of its operations internally.

     EOP Partnership, a Delaware limited partnership, was organized in July
1997. Equity Office, a Maryland real estate investment trust, was organized in
1996 and began operations in 1997 to continue and expand the national office
property business of Mr. Samuel Zell, chairman of the board of trustees of
Equity Office, and his affiliates.

CORNERSTONE PROPERTIES INC.
CORNERSTONE PROPERTIES LIMITED PARTNERSHIP
126 East 56th Street
Tower 56
New York, New York 10022
(212) 605-7100

     Cornerstone Properties Inc. is a self-administered equity REIT which owns,
through subsidiaries, interests in 82 class A office buildings comprising
approximately 18 million rentable square feet, a shopping center, a hotel and
developable land. The Cornerstone properties are primarily located in nine major
metropolitan areas throughout the United States: Atlanta, Boston, suburban
Chicago, Minneapolis, New York City, San Francisco Bay Area, Seattle, Southern
California and Washington, D.C. and surrounding suburbs. Class A office
properties are generally considered to be those that have the most favorable
locations and physical attributes, command premium rents and experience the
highest tenant retention rates within their markets. Cornerstone Properties is
organized as a Nevada corporation.

     In January 1998, Cornerstone converted its corporate structure into an
umbrella limited partnership REIT. Under this structure, Cornerstone is the sole
general partner of, and owns the controlling interest in, Cornerstone Properties
Limited Partnership.

INFORMATION ABOUT THE ACTIONS TAKEN OR TO BE TAKEN BY THE GENERAL PARTNER OF
EOP PARTNERSHIP (SEE PAGE 26)

     Under authority granted in the partnership agreement of EOP Partnership,
Equity Office, as the general partner of EOP Partnership, has determined that
the partnership merger is in the best interests of EOP Partnership and its
unitholders, and has approved the merger agreement and the partnership merger.
No vote or consent of unitholders of EOP Partnership is required under the
partnership agreement of EOP Partnership for approval of the partnership merger.

     The partnership agreement of EOP Partnership requires the approval of the
REIT merger by the consent of unitholders holding at least a majority of the
outstanding EOP Partnership units, including any EOP Partnership units held

                                        1
<PAGE>   14

by Equity Office. As of                , 2000, Equity Office owned approximately
88.2% of the outstanding EOP Partnership units and intends to take action by
written consent, as permitted under the partnership agreement of EOP
Partnership, to approve the REIT merger on or about                , 2000.
Because Equity Office owns more than a majority of the outstanding partnership
units of EOP Partnership, no vote or consent of EOP Partnership unitholders,
other than Equity Office, is required for approval of the REIT merger, and none
is being solicited. Accordingly, under applicable SEC rules, this document is
being forwarded to unitholders of EOP Partnership of record on                ,
2000 for informational purposes only.

CORNERSTONE PARTNERSHIP UNITHOLDERS' CONSENT PROCEDURES (SEE PAGE 27)

     Cornerstone is asking Cornerstone Partnership unitholders to consent to the
mergers. The partnership agreement of Cornerstone Partnership requires the
approval of the mergers by the consent of unitholders holding at least a
majority of the outstanding Cornerstone Partnership units, including any
Cornerstone Partnership units held by Cornerstone. As of             , 2000,
Cornerstone owned approximately 87.1% of the Cornerstone Partnership units.
Cornerstone is required to vote its units in proportion to the manner in which
all outstanding shares of capital stock of Cornerstone are voted at the special
meeting of stockholders of Cornerstone to be held on                , 2000 in
connection with the REIT merger. You may execute a consent to the mergers if you
owned Cornerstone Partnership units on                , 2000.

CORNERSTONE VOTING AGREEMENTS (SEE PAGE 71)

     Cornerstone's directors and executive officers have entered into voting
agreements under which they have agreed to vote all of their Cornerstone
Partnership units and shares of Cornerstone common stock to approve the mergers
and against any alternative acquisition proposals. As of the record date for
consent to the mergers by Cornerstone Partnership unitholders, the directors and
executive officers of Cornerstone, including their affiliates, beneficially
owned 5,056,240 Cornerstone Partnership units, representing approximately 3.4%
of the outstanding Cornerstone Partnership units entitled to consent to the
mergers and           shares of Cornerstone common stock, representing
approximately   % of the outstanding shares of Cornerstone common stock entitled
to vote at the Cornerstone stockholders meeting.

APPROVAL OF THE REIT MERGER BY EQUITY OFFICE COMMON SHAREHOLDERS AND CORNERSTONE
COMMON AND PREFERRED STOCKHOLDERS (SEE PAGE 61)

     By separate joint proxy statement/prospectus, the board of trustees of
Equity Office and the board of directors of Cornerstone are soliciting the
approval of the merger agreement and the REIT merger, as applicable, from the
Equity Office common shareholders and the Cornerstone common and preferred
stockholders, respectively. The joint proxy statement/prospectus also
constitutes a prospectus of Equity Office with regard to the Equity Office
common shares to be issued to the Cornerstone common stockholders in the REIT
merger. Approval of the REIT merger requires the affirmative vote of at least a
majority of the outstanding shares of Cornerstone common stock and at least two
thirds of the outstanding shares of Cornerstone 7% cumulative convertible
preferred stock. Approval of the merger agreement and the REIT merger requires
the affirmative vote of not less than a majority of all votes entitled to be
cast by Equity Office common shareholders. The consummation of REIT merger is
conditioned upon completion of the partnership merger and the partnership merger
will not be completed if the REIT merger does not receive the required approval
of the Equity Office shareholders and Cornerstone stockholders.

RECOMMENDATION OF THE CORNERSTONE BOARD (SEE PAGE 40)

     The Cornerstone board of directors on behalf of Cornerstone, in its
capacity as general partner of Cornerstone Partnership, has approved and adopted
the merger agreement, including the partnership merger and the REIT merger
contemplated thereby. The Cornerstone board of directors believes that the
mergers are in the best interests of Cornerstone, Cornerstone Partnership and
their respective security holders. Cornerstone Partnership unitholders also
should refer to the reasons that the Cornerstone board of directors considered
in determining whether to approve and adopt the merger agreement on pages 40
through 42.

                                        2
<PAGE>   15

THE PARTNERSHIP MERGER (SEE PAGE 30)

     The merger agreement is attached at the back of this consent solicitation
statement/information statement/prospectus as Annex A. We urge you to read the
merger agreement as it is the legal document that governs the partnership merger
and the REIT merger.

     The merger agreement contemplates the following two-step transaction:

     - the partnership merger, whereby Cornerstone Partnership will merge into
       EOP Partnership and Cornerstone Partnership will cease to exist; followed
       by

     - the REIT merger, whereby Cornerstone will merge into Equity Office and
       Cornerstone will cease to exist.

     The REIT merger will be completed immediately after the completion of the
partnership merger.

     The diagram of the structure of the mergers is as follows:

     [DIAGRAM OF STRUCTURE OF THE PARTIES BEFORE THE MERGERS AND AFTER THE
MERGERS]

CONDITIONS TO THE PARTNERSHIP MERGER AND THE REIT MERGER (SEE PAGE 60)

     Before the partnership merger and the REIT merger can be completed, a
number of conditions must be satisfied. These include:

     - approval of the merger agreement and the REIT merger by the requisite
       votes of Cornerstone Partnership unitholders and the EOP Partnership
       unitholders;

     - approval of the merger agreement and the REIT merger by the requisite
       vote of Equity Office common shareholders and approval of the merger
       agreement by the requisite vote of Cornerstone common and preferred
       stockholders;

     - absence of law preventing the consummation of either the partnership
       merger or the REIT merger;

     - delivery of tax opinions that the REIT merger qualifies as a
       reorganization under section 368(a) of the Internal Revenue Code and that
       EOP Partnership will be treated as a partnership under the Internal
       Revenue Code; and

     - other customary closing conditions.

     Where the law permits, Equity Office or EOP Partnership, on the one hand,
or Cornerstone or Cornerstone Partnership, on the other hand, could decide to
complete the partnership merger and the REIT Merger even though one or more
conditions was not satisfied. By law, neither Equity Office or EOP Partnership,
on the one hand, nor Cornerstone or Cornerstone Partnership, on the other hand,
can waive (A) a failure by the requisite vote of shareholders to adopt and
approve the merger agreement and the REIT merger, (B) a failure by the requisite
vote of unitholders of EOP Partnership or Cornerstone Partnership to approve the
merger agreement and the REIT merger or (C) any court order or law preventing
consummation of the partnership merger or the REIT merger. Whether any of the
other conditions would be waived would depend on the facts and circumstances as
determined by the reasonable business judgment of the board of trustees of
Equity Office, acting on its own behalf or in its capacity as general partner of
EOP Partnership, or the board of directors of Cornerstone. If Equity Office and
EOP Partnership or Cornerstone and Cornerstone Partnership waived compliance
with one or more of the conditions and the condition was deemed material to a
vote of Equity Office and/or Cornerstone shareholders or EOP Partnership and/or
Cornerstone Partnership unitholders, Equity Office, Cornerstone and/or
Cornerstone Partnership would have to resolicit the approval by its stockholders
and unitholders, respectively, or, in the case of EOP Partnership, inform its
unitholders of such material change, before the closing of the REIT merger or
the partnership merger.

     It is a condition to the consummation of the REIT merger that Hogan &
Hartson L.L.P., counsel to Equity Office, and King & Spalding, counsel to
Cornerstone, deliver opinions that the REIT merger qualifies as a reorganization
under the provisions of section 368(a) of the Code. This condition will not be
waived.

TERMINATION OF THE MERGER AGREEMENT;
TERMINATION FEES (SEE PAGE 67-68)

     The merger agreement contains provisions addressing the circumstances under
which Equity
                                        3
<PAGE>   16

Office and EOP Partnership, on the one hand, and Cornerstone and Cornerstone
Partnership, on the other hand, may terminate the merger agreement. In addition,
the merger agreement provides that, in several circumstances, Cornerstone may be
required to pay to Equity Office a termination fee of $100 million.

SUMMARY OF MATERIAL FEDERAL INCOME TAX
CONSEQUENCES (SEE PAGE 73)

     A Cornerstone Partnership unitholder who receives only EOP Partnership
units in the partnership merger generally will not recognize taxable gain at the
time of the partnership merger, except to the extent that the unitholder
experiences a reduction in its share of partnership liabilities that exceeds its
adjusted basis in the EOP Partnership units that are received in the partnership
merger. Whether a particular Cornerstone Partnership unitholder will experience
a reduction in its share of partnership liabilities in connection with the
partnership merger will depend upon a number of variables, which are discussed
more fully under the heading "Material Federal Income Tax Consequences -- Tax
Consequences of the Partnership Merger to Cornerstone Partnership Unitholders
That Receive EOP Partnership Units" beginning on page 78. In addition,
subsequent events and transactions could cause a Cornerstone Partnership
unitholder to be required to recognize all or part of the gain deferred at the
time of the partnership merger. See "Material Federal Income Tax
Consequences -- Effect of Subsequent Events" on page 86.

     A Cornerstone Partnership unitholder who exercises its unit redemption
right before the partnership merger and receives Cornerstone common stock in
exchange for its Cornerstone Partnership units will recognize taxable gain equal
to the difference between the "amount realized" for tax purposes and the
Cornerstone Partnership unitholder's adjusted basis in its Cornerstone
Partnership units that are redeemed. If you have a "negative capital account"
with respect to your Cornerstone Partnership units, the gain recognized on the
redemption would exceed the value of the Cornerstone common stock received by
the amount of that negative capital account. A Cornerstone Partnership
unitholder who redeems his units for Cornerstone common stock immediately prior
to the partnership merger will have a basis in the Cornerstone common stock
received equal to the fair market value of that Cornerstone common stock at the
time of the redemption. The unitholder's holding period in the Cornerstone
common stock received will begin after the redemption. See "Material Federal
Income Tax Consequences -- Tax Consequences of the Redemption of Cornerstone
Partnership Units for Cornerstone Common Stock" on page 95.

     A Cornerstone Partnership unitholder who redeems its Cornerstone
Partnership units for Cornerstone common stock before the partnership merger
will participate in the REIT merger as a Cornerstone common stockholder. The
REIT merger is intended to qualify as a reorganization under section 368(a) of
the Internal Revenue Code. Accordingly, a Cornerstone common stockholder who
receives only Equity Office common shares in the REIT merger will not recognize
gain or loss realized on the REIT merger for federal income tax purposes.
However, a Cornerstone common stockholder will be required to recognize any
taxable gain realized with respect to cash received instead of a fractional
Equity Office common share. A Cornerstone common stockholder who receives only
cash in the REIT merger will recognize any taxable gain or loss realized on the
exchange for federal income tax purposes. A Cornerstone common stockholder who
receives both Equity Office common shares and cash will recognize any gain
realized up to the amount of cash received, but will not recognize any loss
realized. See "Material Federal Income Tax Consequences -- Tax Consequences of
the REIT Merger" on page 97.

     The tax consequences of the partnership merger, any redemption, and the
REIT merger to each Cornerstone Partnership unitholder will depend on the
particular situation of that unitholder. Each Cornerstone Partnership
unitholder, therefore, is urged to consult with its own tax advisor for a full
understanding of the tax consequences to the unitholder that will result from
the partnership merger, any redemption of its Cornerstone Partnership units, and
the REIT merger.

ACCOUNTING TREATMENT (SEE PAGE 51)

     The partnership merger and the REIT merger will be treated as a purchase
for financial accounting purposes.
                                        4
<PAGE>   17

CONFLICTS OF INTEREST OF CORNERSTONE DIRECTORS AND OFFICERS IN THE MERGERS (SEE
PAGE 47)

     A number of directors and executive officers of Cornerstone have interests
in the mergers as employees and/or directors that are different from, or in
addition to, yours as a Cornerstone Partnership unitholder. The Cornerstone
board recognized these interests and determined that they did not affect the
benefits of the REIT merger to Cornerstone stockholders or the partnership
merger to Cornerstone Partnership unitholders.

     If the mergers take place, William Wilson III, John S. Moody and Jan H.W.R.
van der Vlist will become members of the Equity Office board of trustees. Also,
indemnification arrangements in the merger agreement and directors' and
officers' liability insurance for existing directors and officers of Cornerstone
will be continued by Equity Office after the mergers.

     In addition, if the mergers take place, options to purchase Cornerstone
common stock held by Cornerstone's directors and officers will be automatically
converted into options to acquire Equity Office common shares adjusted to
account for the exchange ratio of 0.7009. Further, if the mergers are completed
and Cornerstone executives with whom Cornerstone has severance agreements are
terminated under the circumstances described in "The Partnership
Merger -- Interests of Cornerstone's Directors and Officers in the Mergers" then
such persons would be entitled to aggregate benefits, if the employment of all
of these persons is terminated following completion of the mergers, of
approximately $34.7 million under such agreements. Upon the completion of the
REIT merger, outstanding unvested options to purchase an aggregate of 3,675,647
shares of Cornerstone common stock will become exercisable in full. Of these,
Messrs. Wilson, Moody and the other Cornerstone executives with severance
agreements hold unvested options to purchase 3,177,476 shares of Cornerstone
common stock at a per share weighted average exercise price of $16.48. Under the
merger agreement, Cornerstone optionees may elect to cash-out their vested
options, after completion of the REIT merger and before the end of the second
business day following completion of the REIT merger, for an amount of cash
equal to the excess, if any, of $18.00 over the exercise price multiplied by the
number of shares of Cornerstone common stock subject to the options.

TRUSTEES OF EQUITY OFFICE FOLLOWING THE REIT MERGER (SEE PAGE 49)

     The merger agreement provides that Messrs. Moody, Wilson and van der Vlist
will become members of the board of trustees of Equity Office, with terms
expiring in 2002, 2003 and 2003, respectively. In addition, Equity Office has
agreed to renominate Mr. van der Vlist, or a replacement designated by Stichting
Pensioenfonds voor de Gezondheid, Geestelijke en MaatschapelijkeBelangen, or
PGGM, and subject to the approval of Equity Office if such replacement is not an
officer, director or employee of PGGM, to the board of trustees of Equity Office
upon the expiration of his terms in 2003 and 2006, so long as PGGM and its
affiliates continue to own in the aggregate at 21,000,000 or more of the issued
and outstanding Equity Office common shares.

DIFFERENCES IN THE RIGHTS OF UNITHOLDERS AND SHAREHOLDERS (SEE PAGES 132 AND
146)

     Delaware law and the partnership agreement of Cornerstone Partnership
currently govern the rights of Cornerstone Partnership unitholders. Upon
completion of the partnership merger, Cornerstone Partnership unitholders either
will become Equity Office common shareholders, with rights governed by Maryland
law and Equity Office's declaration of trust and bylaws or EOP Partnership
unitholders, with rights governed by Delaware law and the partnership agreement
of EOP Partnership, depending on whether or not a Cornerstone unitholder redeems
its units of Cornerstone common stock prior to the partnership merger.

                                        5
<PAGE>   18

PARTNERSHIP MERGER SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA

     EOP PARTNERSHIP

     The following table sets forth selected consolidated and combined financial
and operating information on a historical basis for EOP Partnership and its
predecessors. The selected financial data has been derived from the historical
consolidated or combined financial statements of EOP Partnership and its
predecessors, audited by Ernst & Young LLP, independent auditors. The following
information should be read in conjunction with the consolidated and combined
financial statements and financial statement notes of EOP Partnership and its
predecessors incorporated by reference in this consent solicitation/information
statement/prospectus. See "Where You Can Find More Information" on page 163.

<TABLE>
<CAPTION>
                                  EOP OPERATING LIMITED PARTNERSHIP              EOP PARTNERSHIP PREDECESSORS
                             -------------------------------------------   -----------------------------------------
                                                              FOR THE          FOR THE
                                                              PERIOD           PERIOD
                                    FOR THE YEARS              FROM             FROM              FOR THE YEARS
                                        ENDED              JULY 11, 1997   JANUARY 1, 1997            ENDED
                                    DECEMBER 31,              THROUGH          THROUGH            DECEMBER 31,
                             ---------------------------   DECEMBER 31,       JULY 10,       -----------------------
                                 1999           1998           1997             1997            1996         1995
                             ------------   ------------   -------------   ---------------   ----------   ----------
                                                  (DOLLARS IN THOUSANDS, EXCEPT PER UNIT DATA)
<S>                          <C>            <C>            <C>             <C>               <C>          <C>
OPERATING DATA:
Revenues:
  Rental, parking and
    other..................  $  1,919,056   $  1,658,420   $    406,713       $ 327,017      $  493,396   $  356,959
                             ------------   ------------   ------------       ---------      ----------   ----------
         Total revenues....     1,942,243      1,679,699        412,968         339,104         508,124      371,457
                             ------------   ------------   ------------       ---------      ----------   ----------
Expenses:
  Interest.................       413,995        338,611         76,675          80,481         119,595      100,566
  Depreciation and
    amortization...........       358,989        305,982         70,346          66,034          96,237       74,156
  Property operating and
    ground rent (1)........       669,763        600,367        155,679         127,285         201,067      151,488
  General and
    administrative.........        80,927         63,564         17,690          17,201          23,145       21,987
  Provision for value
    impairment.............            --             --             --              --              --       20,248
                             ------------   ------------   ------------       ---------      ----------   ----------
         Total expenses....     1,523,674      1,308,524        320,390         291,001         440,044      368,445
                             ------------   ------------   ------------       ---------      ----------   ----------
Income before allocation to
  minority interests,
  income from investment in
  unconsolidated joint
  ventures, net gain(loss)
  on sales of real estate
  and extraordinary
  items....................       418,569        371,175         92,578          48,103          68,080        3,012
Minority interests.........        (1,981)        (2,114)          (789)           (912)         (2,086)      (2,129)
Income from investment in
  unconsolidated joint
  ventures.................        13,824         11,267          3,173           1,982           2,093        2,305
Net gain(loss) on sales of
  real estate and
  extraordinary items......        49,113          4,927        (16,240)         12,236           5,338       31,271
                             ------------   ------------   ------------       ---------      ----------   ----------
Net income.................       479,525        385,255         78,722          61,409          73,425       34,459
Put option settlement......        (5,658)            --             --              --              --           --
Preferred distributions....       (43,603)       (32,202)          (649)             --              --           --
                             ------------   ------------   ------------       ---------      ----------   ----------
Net income available for
  units....................  $    430,264   $    353,053   $     78,073       $  61,409      $   73,425   $   34,459
                             ============   ============   ============       =========      ==========   ==========
Net income available per
  weighted average unit
  outstanding -- basic.....  $       1.49   $       1.25   $       0.44
                             ============   ============   ============
Net income available per
  weighted average unit
  outstanding -- diluted...  $       1.48   $       1.24   $       0.43
                             ============   ============   ============
Weighted average units
  outstanding -- basic.....   288,326,547    282,114,343    178,647,562
                             ============   ============   ============
Weighted average units
  outstanding -- diluted...   291,157,204    283,974,532    180,014,027
                             ============   ============   ============
</TABLE>

                                        6
<PAGE>   19

<TABLE>
<CAPTION>
                                  EOP OPERATING LIMITED PARTNERSHIP              EOP PARTNERSHIP PREDECESSORS
                             -------------------------------------------   -----------------------------------------
                                                              FOR THE          FOR THE
                                                              PERIOD           PERIOD
                                    FOR THE YEARS              FROM             FROM              FOR THE YEARS
                                        ENDED              JULY 11, 1997   JANUARY 1, 1997            ENDED
                                    DECEMBER 31,              THROUGH          THROUGH            DECEMBER 31,
                             ---------------------------   DECEMBER 31,       JULY 10,       -----------------------
                                 1999           1998           1997             1997            1996         1995
                             ------------   ------------   -------------   ---------------   ----------   ----------
                                                  (DOLLARS IN THOUSANDS, EXCEPT PER UNIT DATA)
<S>                          <C>            <C>            <C>             <C>               <C>          <C>
BALANCE SHEET DATA (at end
  of period):
  Investment in real
    estate, net of
    accumulated
    depreciation...........  $ 12,572,153   $ 13,331,560   $ 10,976,319              --      $3,291,815   $2,393,403
  Total assets.............  $ 14,046,058   $ 14,261,291   $ 11,751,672              --      $3,912,565   $2,650,890
  Mortgage debt, unsecured
    notes and lines of
    credit.................  $  5,851,918   $  6,025,405   $  4,284,317              --      $1,964,892   $1,434,827
  Total liabilities........  $  6,336,531   $  6,472,613   $  4,591,697              --      $2,174,483   $1,529,334
  Minority interests.......  $     39,027   $     28,360   $     29,612              --      $   11,080   $   31,587
  Preferred units..........  $    615,000   $    615,000   $    200,000              --              --           --
  Partners' Capital/Owners'
    equity.................  $  7,055,500   $  7,145,318   $  6,930,363              --      $1,727,002   $1,089,969
OTHER DATA:
  General and
    administrative expenses
    as a percentage of
    total revenues.........           4.2%           3.8%           4.3%            5.1%            4.6%         5.9%
  Number of office
    properties.............           294            284            258              --              84           73
  Net rentable square feet
    of office properties
    (in millions)..........          77.0           75.1           65.3              --            29.2         23.1
  Occupancy of office
    properties.............            94%            95%            94%             --              90%          86%
  Number of parking
    facilities.............            20             19             17              --              10            3
  Number of spaces at
    parking facilities.....        20,506         18,059         16,749              --           7,321        3,323
  Funds from
    Operations(2)..........  $    748,983   $    662,585   $    163,253       $ 113,022      $  160,460   $   96,104
                             ============   ============   ============       =========      ==========   ==========
  Property net operating
    income (3).............  $  1,256,180   $  1,065,714   $    253,418       $ 202,108      $  294,556   $  206,341
                             ============   ============   ============       =========      ==========   ==========
  Earnings before interest,
    taxes, depreciation,
    and amortization (4)...  $  1,228,913   $  1,049,577   $    242,969       $ 197,489      $  286,128   $  200,438
                             ============   ============   ============       =========      ==========   ==========
  Cash flow provided by
    operating activities...  $    720,711   $    759,151   $    190,754       $  95,960      $  165,975   $   93,878
                             ============   ============   ============       =========      ==========   ==========
  Cash flow (used for)
    investing activities...  $    (67,138)  $ (2,231,712)  $ (1,592,272)      $(571,068)     $ (924,227)  $ (380,615)
                             ============   ============   ============       =========      ==========   ==========
  Cash flow (used for)
    provided by financing
    activities.............  $   (718,315)  $  1,310,788   $  1,630,346       $ 245,851      $1,057,551   $  276,513
                             ============   ============   ============       =========      ==========   ==========
</TABLE>

- ---------------
(1) Property operating expenses includes real estate taxes, insurance, repairs
    and maintenance and other property operating expenses.

(2) The White Paper on Funds from Operations approved by the Board of Governors
    of the National Association of Real Estate Investment Trusts ("NAREIT") in
    March 1995 defines Funds from Operations as net income (loss), computed in
    accordance with GAAP, excluding gains (or losses) from debt restructuring
    and sales of properties, plus real estate related depreciation and
    amortization and after adjustments for unconsolidated partnerships and joint
    ventures. EOP Partnership believes that Funds from Operations is helpful to
    investors as a measure of the performance of an equity REIT because, along
    with cash flow from operating, investing and financing activities, it
    provides investors with an indication of the ability of EOP Partnership to
    incur and service debt, to make capital expenditures and to fund other cash
    needs. EOP Partnership computes Funds from Operations in accordance with
    standards established by NAREIT, which may not be comparable to Funds from
    Operations reported by other REITs that do not define the term in accordance
    with the current

                                        7
<PAGE>   20

    ]NAREIT definition or that interpret the current NAREIT definition
    differently than EOP Partnership. Funds from Operations does not represent
    cash generated from operating activities in accordance with GAAP, nor does
    it represent cash available to pay distributions and should not be
    considered as an alternative to net income, determined in accordance with
    GAAP, as an indication of EOP Partnership's financial performance or to cash
    flow from operating activities, determined in accordance with GAAP, as a
    measure of EOP Partnership's liquidity, nor is it indicative of funds
    available to fund EOP Partnership's cash needs, including its ability to
    make cash distributions.

(3) Property net operating income is defined as rental income including tenant
    reimbursements, parking and other income less property operating expenses
    including real estate taxes, insurance, repairs and maintenance and other
    property operating expenses.

(4) Earnings before interest, taxes, depreciation and amortization is defined as
    net income excluding interest expense, taxes, depreciation and amortization,
    net gain (loss) on sales of real estate, gains (losses) from extraordinary
    items and income from investment in unconsolidated joint ventures plus EOP
    Partnership's share of the earnings before interest, taxes, depreciation and
    amortization for the unconsolidated joint ventures. Earnings before
    interest, taxes, depreciation and amortization is presented because EOP
    Partnership believes this data is used by some investors to evaluate EOP
    Partnership's ability to meet debt service requirements. EOP Partnership
    considers earnings before interest, taxes, depreciation and amortization to
    be an indicative measure of its operating performance due to the
    significance of EOP Partnership's long-lived assets and because this data
    can be used to measure EOP Partnership's ability to service debt, fund
    capital expenditures and expand its business. However, this data should not
    be considered as an alternative to net income, operating profit, cash flows
    from operations or any other operating or liquidity performance measure
    prescribed by GAAP. In addition, earnings before interest, taxes,
    depreciation and amortization as calculated by EOP Partnership may not be
    comparable to similarly titled measures reported by other companies.
    Interest expense, taxes, depreciation and amortization, which are not
    reflected in the presentation of earnings before interest, taxes,
    depreciation and amortization, have been, and will be, incurred by EOP
    Partnership. Investors are cautioned that these excluded items are
    significant components in understanding and assessing EOP Partnership's
    financial performance.

                                        8
<PAGE>   21

     CORNERSTONE PARTNERSHIP

     The following table sets forth selected consolidated financial and
operating information on a historical basis for Cornerstone Partnership. The
selected consolidated operating and balance sheet data of Cornerstone
Partnership as of and for the year ended December 31, 1999 have been derived
from the historical consolidated financial statements audited by
PricewaterhouseCoopers LLP, independent accountants. The selected consolidated
operating and balance sheet data as of and for the year ended December 31, 1998
has been derived from unaudited financial statements of Cornerstone Partnership
and include all adjustments consisting of only normal recurring adjustments that
Cornerstone Partnership's management considers necessary for a fair presentation
of the financial position and results of operations for the year. The following
information should be read in conjunction with the consolidated financial
statements and financial statement notes of Cornerstone Partnership included in
this consent solicitation/information statement/prospectus. See "Cornerstone
Partnership Historical Consolidated Financial Statements" on page F-20.

<TABLE>
<CAPTION>
                                                                 1999          1998
                                                              -----------   -----------
                                                              (IN THOUSANDS, EXCEPT PER
                                                                    UNIT AMOUNTS)
<S>                                                           <C>           <C>
BALANCE SHEET DATA:
Real estate investments before accumulated depreciation.....  $3,951,465    $4,262,136
Total assets................................................   4,170,228     4,281,658
Long-term debt..............................................   1,435,405     1,519,548
Credit facility.............................................     329,000       465,000
Total liabilities...........................................   1,877,645     2,125,323
Redeemable preferred units..................................  $       --    $       --
OPERATING DATA:
Revenues....................................................  $  616,316    $  339,337
Expenses....................................................     464,929       248,438
Gain (loss) on sale of real estate assets...................     131,034          (173)
Minority interest...........................................      (5,755)       (4,399)
Cumulative effect of a change in accounting principle.......        (630)           --
Extraordinary loss..........................................     (10,787)       (4,303)
Net income..................................................  $  265,249    $   82,024
Net income per unit, basic..................................  $     1.76    $     0.76
Net income per unit, diluted................................  $     1.75    $     0.75
Distributions declared per unit.............................  $     0.90    $     1.50
OTHER DATA:
Cash Flow from:
  Operations................................................  $  223,115    $  173,612
  Investing.................................................      52,488      (849,830)
  Financing.................................................    (317,536)      737,830
  Funds From Operations (1).................................  $  242,040    $  147,535
</TABLE>

<TABLE>
<S>                                                           <C>
</TABLE>

- ---------------
(1) Funds From Operations is a calculation which is defined by NAREIT and is not
    indicative of either net income or cash flow from operations as calculated
    in accordance with GAAP as a measure of performance or liquidity. As
    disclosed in Cornerstone Partnership's Management Discussion and Analysis of
    Financial Condition and Results of Operation on page 117, Cornerstone
    Partnership makes certain additional adjustments to Funds From Operations
    which are not contemplated in the NAREIT definition.

     EQUIVALENT PER UNIT DATA

     We have summarized below the per unit information for our respective
partnerships on an historical basis, pro forma combined basis and pro forma
combined equivalent basis. The pro forma combined
                                        9
<PAGE>   22

summary amounts are based on the purchase method of accounting. The Cornerstone
Partnership per unit pro forma combined equivalents are calculated by
multiplying the pro forma combined per unit amounts by the exchange ratio of
0.7009. Cornerstone Partnership unitholders who receive EOP Partnership units in
the partnership merger will receive 0.7009 of an EOP Partnership unit in
exchange for each Cornerstone Partnership unit. You should note that, in 1999,
Cornerstone Partnership declared distributions equal to $.90 per Cornerstone
Partnership unit but paid distributions equal to $1.20 per Cornerstone
Partnership unit.

     The following information should be read together with the historical and
pro forma financial statements included or incorporated by reference in this
document. See "Where You Can Find More Information" on page 163.

<TABLE>
<CAPTION>
                                                              FOR THE YEAR ENDED
                                                              DECEMBER 31, 1999
                                                              ------------------
                                                              BASIC      DILUTED
                                                              -----      -------
<S>                                                           <C>        <C>
NET INCOME PER UNIT(1):
  EOP Partnership...........................................  $1.49       $1.48
  Cornerstone Partnership...................................  $1.76       $1.75
  EOP Partnership and Cornerstone Partnership pro forma
     combined before extraordinary items and cumulative
     effect of a change in accounting principle.............  $1.77       $1.76
  Cornerstone Partnership pro forma combined equivalent.....  $1.24       $1.23
</TABLE>

- ---------------
(1) The net income per unit amounts include the gain on sales of real estate in
    1999 for EOP Partnership and Cornerstone Partnership. Such gains can
    fluctuate substantially from year to year. Therefore, the following table
    reflects net income per unit before extraordinary items, the cumulative
    effect of a change in accounting principle and the gain on sales of real
    estate for EOP Partnership and Cornerstone Partnership, net of effect of
    minority interest:

<TABLE>
<CAPTION>
                                                              BASIC   DILUTED
                                                              -----   -------
<S>                                                           <C>     <C>
       NET INCOME BEFORE EXTRAORDINARY ITEMS, THE CUMULATIVE
        EFFECT OF A CHANGE IN ACCOUNTING PRINCIPLE AND GAIN
        ON SALES OF REAL ESTATE PER UNIT, NET OF EFFECT OF
        MINORITY INTEREST:
          EOP Partnership...................................  $1.32    $1.31
          Cornerstone Partnership...........................  $0.96    $0.96
          EOP Partnership and Cornerstone Partnership pro
           forma combined...................................  $1.23    $1.22
          Cornerstone Partnership pro forma combined
           equivalent.......................................  $0.86    $0.86
</TABLE>

<TABLE>
<CAPTION>
                                                              FOR THE YEAR ENDED
                                                              DECEMBER 31, 1999
                                                              ------------------
<S>                                                           <C>
CASH DISTRIBUTIONS DECLARED PER UNIT:
  EOP Partnership...........................................        $ 1.58
  Cornerstone Partnership...................................        $ 0.90
  EOP Partnership and Cornerstone Partnership pro forma
     combined...............................................        $ 1.58
  Cornerstone Partnership pro forma combined equivalent.....        $ 1.11
PARTNERS' CAPITAL (BOOK VALUE) PER UNIT (END OF PERIOD):
  EOP Partnership...........................................        $24.69
  Cornerstone Partnership...................................        $14.96
  EOP Partnership and Cornerstone Partnership pro forma
     combined...............................................        $24.69
  Cornerstone Partnership pro forma combined equivalent.....        $17.31
</TABLE>

     PRICES OF EOP PARTNERSHIP UNITS AND CORNERSTONE PARTNERSHIP UNITS

     The EOP Partnership units and the Cornerstone Partnership units are not
listed on any national securities exchange or quoted in the over the counter
market, and there is no established public trading

                                       10
<PAGE>   23

market for either the EOP Partnership units or the Cornerstone Partnership
units. However, each EOP Partnership unit to be received by Cornerstone
Partnership unitholders in the partnership merger may be redeemed for one Equity
Office common share or its cash equivalent, at Equity Office's option. Under the
partnership agreement of Cornerstone Partnership, those Cornerstone Partnership
units issued more than one year ago may be redeemed for Cornerstone common
shares or, at the option of Cornerstone, the cash equivalent thereof. The
following table sets forth the price per share of Equity Office common shares
and Cornerstone common stock based on the last reported sale prices per share on
the NYSE on February 10, 2000, the last trading day prior to the public
announcement of the execution of the merger agreement, and on                ,
2000, the most recent date for which prices are available prior to mailing this
consent solicitation/information statement/prospectus.

<TABLE>
<CAPTION>
                                                                        PRICE PER SHARE
                                                                                       CORNERSTONE PRO
                                                       EQUITY OFFICE   CORNERSTONE   FORMA EQUIVALENT(1)
                                                       -------------   -----------   -------------------
<S>                                                    <C>             <C>           <C>
February 10, 2000....................................    $25.6875        $14.875           $18.00
               , 2000(2).............................    $               $                 $
</TABLE>

- ---------------
(1) Computed by multiplying the Equity Office common share closing price by the
    0.7009 exchange ratio.

(2) The average last reported sale price per Equity Office common share for the
    five trading days preceding           , 2000 was $ . The Cornerstone pro
    forma equivalent, based on such five trading days, would be $ .

                                       11
<PAGE>   24

PARTNERSHIP MERGER SUMMARY UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL DATA

     The following table sets forth the summary unaudited pro forma combined
financial data for EOP Partnership and Cornerstone Partnership as a combined
entity, giving effect to the partnership merger as if it had occurred on the
dates indicated herein and after giving effect to the pro forma adjustments. The
unaudited pro forma combined operating data are presented as if the partnership
merger had been consummated on January 1, 1999. The unaudited pro forma combined
balance sheet data at December 31, 1999 is presented as if the partnership
merger had occurred on December 31, 1999. In the opinion of management of Equity
Office, all adjustments necessary to reflect the effects of these transactions
have been made. The partnership merger will be accounted for under the purchase
method of accounting in accordance with Accounting Principles Board Opinion No.
16.

     The pro forma financial information should be read in conjunction with, and
is qualified in its entirety by, the respective historical audited financial
statements and financial statement notes of EOP Partnership incorporated by
reference into this consent solicitation/information statement/prospectus and of
Cornerstone Partnership. See "Where You Can Find More Information" on page 163
and "Cornerstone Partnership Historical Financial Statements" on page F-20. The
unaudited pro forma operating data are presented for comparative purposes only
and are not necessarily indicative of what the actual combined results of
operations of EOP Partnership and Cornerstone Partnership would have been for
the period presented, nor does such data purport to represent the results of
future periods. See "EOP Operating Limited Partnership Pro Forma Condensed
Combined Financial Statements" on page F-2.

<TABLE>
<CAPTION>
                                                                       PRO FORMA
                                                                   FOR THE YEAR ENDED
                                                                   DECEMBER 31, 1999
                                                              ----------------------------
                                                                 (DOLLARS IN THOUSANDS,
                                                                 EXCEPT PER UNIT DATA)
<S>                                                           <C>
OPERATING DATA:
Revenues:
  Rental....................................................          $  1,954,581
  Tenant reimbursement......................................               402,743
  Parking...................................................               139,547
  Other.....................................................                36,896
  Fee income................................................                11,616
  Interest/dividends........................................                18,459
                                                                      ------------
          Total revenues....................................             2,563,842
                                                                      ------------
Expenses:
  Interest:
       Expense incurred.....................................          $    639,859
       Amortization of deferred financing costs.............                10,366
  Depreciation..............................................               442,831
  Amortization..............................................                14,545
  Real estate taxes.........................................               315,332
  Insurance.................................................                13,137
  Repairs and maintenance...................................               284,358
  Property operating........................................               252,826
  Ground rent...............................................                 8,294
  General and administrative................................               107,933
                                                                      ------------
       Total expenses.......................................             2,089,481
                                                                      ------------
Income before allocation to minority interests, income from
  investment in unconsolidated joint ventures and net gain
  on sales of real estate...................................               474,361
Minority interests -- partially owned properties............                (7,736)
Income from investment in unconsolidated joint ventures.....                14,546
</TABLE>

                                       12
<PAGE>   25

<TABLE>
<CAPTION>
                                                                       PRO FORMA
                                                                   FOR THE YEAR ENDED
                                                                   DECEMBER 31, 1999
                                                              ----------------------------
                                                                 (DOLLARS IN THOUSANDS,
                                                                 EXCEPT PER UNIT DATA)
<S>                                                           <C>
Net gain on sales of real estate............................               190,695
                                                                      ------------
Net income from continuing operations.......................               671,866
Put option settlement.......................................                (5,658)
Preferred distributions.....................................               (43,603)
                                                                      ------------
Net income from continuing operations before extraordinary
  items and cumulative effect of a change in accounting
  principle available for units.............................          $    622,605
                                                                      ============
Net income from continuing operations before extraordinary
  items and cumulative effect of a change in accounting
  principle per weighted average unit outstanding --basic...          $       1.77
                                                                      ============
Weighted average units outstanding -- basic.................           351,114,475
                                                                      ============
Net income from continuing operations before extraordinary
  items and cumulative effect of a change in accounting
  principle per weighted average unit
  outstanding -- diluted....................................          $       1.76
                                                                      ============
Weighted average units outstanding -- diluted...............           354,965,413
                                                                      ============
BALANCE SHEET DATA (AT END OF PERIOD):
  Investment in real estate net of accumulated
     depreciation...........................................          $ 16,848,787
                                                                      ============
  Total assets..............................................          $ 18,659,040
                                                                      ============
  Total debt................................................          $  8,779,344
                                                                      ============
  Total liabilities.........................................          $  9,377,262
                                                                      ============
  Minority interests........................................          $     61,559
                                                                      ============
  Partners' capital.........................................          $  9,220,219
                                                                      ============
</TABLE>

                                       13
<PAGE>   26

REIT MERGER SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA

     EQUITY OFFICE

     The following table sets forth selected consolidated and combined financial
and operating information on a historical basis for Equity Office and its
predecessors. The selected financial data has been derived from the historical
consolidated or combined financial statements of Equity Office and its
predecessors, audited by Ernst & Young LLP, independent auditors. The following
information should be read in conjunction with the consolidated and combined
financial statements and financial statement notes of Equity Office and its
predecessors incorporated by reference in this consent solicitation/information
statement/prospectus. See "Where You Can Find More Information" on page 163.

<TABLE>
<CAPTION>
                                   EQUITY OFFICE PROPERTIES TRUST                 EQUITY OFFICE PREDECESSORS
                             -------------------------------------------   -----------------------------------------
                                                              FOR THE          FOR THE
                                                              PERIOD           PERIOD
                                    FOR THE YEARS              FROM             FROM              FOR THE YEARS
                                        ENDED              JULY 11, 1997   JANUARY 1, 1997            ENDED
                                    DECEMBER 31,              THROUGH          THROUGH            DECEMBER 31,
                             ---------------------------   DECEMBER 31,       JULY 10,       -----------------------
                                 1999           1998           1997             1997            1996         1995
                             ------------   ------------   -------------   ---------------   ----------   ----------
                                                  (DOLLARS IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                          <C>            <C>            <C>             <C>               <C>          <C>
Revenues:
Rental, parking and
  other....................  $  1,919,056   $  1,658,420   $    406,713       $ 327,017      $  493,396   $  356,959
                             ------------   ------------   ------------       ---------      ----------   ----------
         Total revenues....     1,942,243      1,679,699        412,968         339,104         508,124      371,457
                             ------------   ------------   ------------       ---------      ----------   ----------
Expenses:
  Interest.................       413,995        338,611         76,675          80,481         119,595      100,566
  Depreciation and
    amortization...........       358,989        305,982         70,346          66,034          96,237       74,156
  Property operating and
    ground rent(1).........       669,763        600,367        155,679         127,285         201,067      151,488
  General and
    administrative.........        80,927         63,564         17,690          17,201          23,145       21,987
  Provision for value
    impairment.............            --             --             --              --              --       20,248
                             ------------   ------------   ------------       ---------      ----------   ----------
         Total expenses....     1,523,674      1,308,524        320,390         291,001         440,044      368,445
                             ------------   ------------   ------------       ---------      ----------   ----------
Income before allocation to
  minority interests,
  income from investment in
  unconsolidated joint
  ventures, net gain/(loss)
  on sales of real estate
  and extraordinary
  items....................       418,569        371,175         92,578          48,103          68,080        3,012
Minority interests.........       (50,153)       (38,340)        (7,799)           (912)         (2,086)      (2,129)
Income from investment in
  unconsolidated joint
  ventures.................        13,824         11,267          3,173           1,982           2,093        2,305
Net gain(loss) on sales of
  real estate and
  extraordinary items......        49,113          4,927        (16,240)         12,236           5,338       31,271
                             ------------   ------------   ------------       ---------      ----------   ----------
Net income.................       431,353        349,029         71,712          61,409          73,425       34,459
Put option settlement......        (5,658)            --             --              --              --           --
Preferred distributions....       (43,603)       (32,202)          (649)             --              --           --
                             ------------   ------------   ------------       ---------      ----------   ----------
Net income available for
  common shares............  $    382,092   $    316,827   $     71,063       $  61,409      $   73,425   $   34,459
                             ============   ============   ============       =========      ==========   ==========
Net income available per
  weighted average common
  share
  outstanding -- basic.....  $       1.49   $       1.25   $       0.44
                             ============   ============   ============
Net income available per
  weighted average common
  share
  outstanding -- diluted...  $       1.48   $       1.24   $       0.43
                             ============   ============   ============
</TABLE>

                                       14
<PAGE>   27

<TABLE>
<CAPTION>
                                   EQUITY OFFICE PROPERTIES TRUST                 EQUITY OFFICE PREDECESSORS
                             -------------------------------------------   -----------------------------------------
                                                              FOR THE          FOR THE
                                                              PERIOD           PERIOD
                                    FOR THE YEARS              FROM             FROM              FOR THE YEARS
                                        ENDED              JULY 11, 1997   JANUARY 1, 1997            ENDED
                                    DECEMBER 31,              THROUGH          THROUGH            DECEMBER 31,
                             ---------------------------   DECEMBER 31,       JULY 10,       -----------------------
                                 1999           1998           1997             1997            1996         1995
                             ------------   ------------   -------------   ---------------   ----------   ----------
                                                  (DOLLARS IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                          <C>            <C>            <C>             <C>               <C>          <C>
Weighted average common
  shares
  outstanding -- basic.....   256,045,895    253,167,037    162,591,477
                             ============   ============   ============
Weighted average common
  shares
  outstanding -- diluted...   291,157,204    283,974,532    180,014,027
                             ============   ============   ============
BALANCE SHEET DATA (at end
  of period):
  Investment in real
    estate, net of
    accumulated
    depreciation...........  $ 12,572,153   $ 13,331,560   $ 10,976,319              --      $3,291,815   $2,393,403
  Total assets.............  $ 14,046,058   $ 14,261,291   $ 11,751,672              --      $3,912,565   $2,650,890
  Mortgage debt, unsecured
    notes and lines of
    credit.................  $  5,851,918   $  6,025,405   $  4,284,317              --      $1,964,892   $1,434,827
  Total liabilities........  $  6,336,531   $  6,472,613   $  4,591,697              --      $2,174,483   $1,529,334
  Minority interests.......  $    883,454   $    737,715   $    754,818              --      $   11,080   $   31,587
  Preferred shares.........  $    615,000   $    615,000   $    200,000              --              --           --
  Shareholders' equity/
    Owners' equity.........  $  6,211,073   $  6,435,963   $  6,205,157              --      $1,727,002   $1,089,969
OTHER DATA:
  General and
    administrative expenses
    as a percentage of
    total revenues.........           4.2%           3.8%           4.3%            5.1%            4.6%         5.9%
  Number of office
    properties.............           294            284            258              --              84           73
  Net rentable square feet
    of office properties
    (in millions)..........          77.0           75.1           65.3              --            29.2         23.1
  Occupancy of office
    properties.............            94%            95%            94%             --              90%          86%
  Number of parking
    facilities.............            20             19             17              --              10            3
  Number of spaces at
    parking facilities.....        20,506         18,059         16,749              --           7,321        3,323
  Funds from
    Operations(2)..........  $    748,983   $    662,585   $    163,253       $ 113,022      $  160,460   $   96,104
                             ============   ============   ============       =========      ==========   ==========
  Property net operating
    income(3)..............  $  1,256,180   $  1,065,714   $    253,418       $ 202,108      $  294,556   $  206,341
                             ============   ============   ============       =========      ==========   ==========
  Earnings before interest,
    taxes, depreciation,
    and amortization(4)....  $  1,228,913   $  1,049,577   $    242,969       $ 197,489      $  286,128   $  200,438
                             ============   ============   ============       =========      ==========   ==========
  Cash flow provided by
    operating activities...  $    720,711   $    759,151   $    190,754       $  95,960      $  165,975   $   93,878
                             ============   ============   ============       =========      ==========   ==========
  Cash flow (used for)
    investing activities...  $    (67,138)  $ (2,231,712)  $ (1,592,272)      $(571,068)     $ (924,227)  $ (380,615)
                             ============   ============   ============       =========      ==========   ==========
  Cash flow (used for)
    provided by financing
    activities.............  $   (718,315)  $  1,310,788   $  1,630,346       $ 245,851      $1,057,551   $  276,513
                             ============   ============   ============       =========      ==========   ==========
</TABLE>

                                       15
<PAGE>   28

- ---------------
(1) Property operating expenses includes real estate taxes, insurance, repairs
    and maintenance and other property operating expenses.

(2) The White Paper on Funds from Operations approved by the Board of Governors
    of NAREIT in March 1995 defines Funds from Operations as net income (loss),
    computed in accordance with GAAP, excluding gains (or losses) from debt
    restructuring and sales of properties, plus real estate related depreciation
    and amortization and after adjustments for unconsolidated partnerships and
    joint ventures. Equity Office believes that Funds from Operations is helpful
    to investors as a measure of the performance of an equity REIT because,
    along with cash flow from operating, investing and financing activities, it
    provides investors with an indication of the ability of Equity Office to
    incur and service debt, to make capital expenditures and to fund other cash
    needs. Equity Office computes Funds from Operations in accordance with
    standards established by NAREIT, which may not be comparable to Funds from
    Operations reported by other REITs that do not define the term in accordance
    with the current NAREIT definition or that interpret the current NAREIT
    definition differently than Equity Office. Funds from Operations does not
    represent cash generated from operating activities in accordance with GAAP,
    nor does it represent cash available to pay distributions and should not be
    considered as an alternative to net income, determined in accordance with
    GAAP, as an indication of Equity Office's financial performance or to cash
    flow from operating activities, determined in accordance with GAAP, as a
    measure of Equity Office's liquidity, nor is it indicative of funds
    available to fund Equity Office's cash needs, including its ability to make
    cash distributions.

(3) Property net operating income is defined as rental income including tenant
    reimbursements, parking and other income less property operating expenses
    including real estate taxes, insurance, repairs and maintenance and other
    property operating expenses.

(4) Earnings before interest, taxes, depreciation and amortization is defined as
    net income excluding interest expense, taxes, depreciation and amortization,
    minority interest allocation to EOP Partnership, net gain/loss on sales of
    real estate, gains/losses from extraordinary items and income from
    investment in unconsolidated joint ventures plus Equity Office's share of
    the earnings before interest, taxes, depreciation and amortization for the
    unconsolidated joint ventures. Earnings before interest, taxes, depreciation
    and amortization is presented because Equity Office believes this data is
    used by some investors to evaluate Equity Office's ability to meet debt
    service requirements. Equity Office considers earnings before interest,
    taxes, depreciation and amortization to be an indicative measure of its
    operating performance due to the significance of Equity Office's long-lived
    assets and because this data can be used to measure Equity Office's ability
    to service debt, fund capital expenditures and expand its business. However,
    this data should not be considered as an alternative to net income,
    operating profit, cash flows from operations or any other operating or
    liquidity performance measure prescribed by GAAP. In addition, earnings
    before interest, taxes, depreciation and amortization as calculated by
    Equity Office may not be comparable to similarly titled measures reported by
    other companies. Interest expense, taxes, depreciation and amortization,
    which are not reflected in the presentation of earnings before interest,
    taxes, depreciation and amortization, have been, and will be, incurred by
    Equity Office. Investors are cautioned that these excluded items are
    significant components in understanding and assessing Equity Office's
    financial performance.

     CORNERSTONE

     The following table sets forth selected consolidated financial and
operating information on a historical basis for Cornerstone. The selected
financial data has been derived from the historical consolidated financial
statements of Cornerstone audited by PricewaterhouseCoopers LLP, independent
accountants. The following information should be read in conjunction with the
consolidated financial statements and financial statement notes of Cornerstone
incorporated by reference in this consent solicitation/information
statement/prospectus. See "Where You Can Find More Information" on page 163.

                                       16
<PAGE>   29

<TABLE>
<CAPTION>
                                    1999          1998          1997         1996        1995
                                 ----------    ----------    ----------    --------    ---------
                                            (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                              <C>           <C>           <C>           <C>         <C>
BALANCE SHEET DATA:
Real estate investments before
  accumulated depreciation.....  $3,951,465    $4,262,136    $1,947,272    $799,662    $ 706,988
Total assets...................   4,170,228     4,281,984     2,051,481     766,180      586,089
Long-term debt.................   1,448,331     1,532,474       706,178     400,142      369,600
Credit facility................     329,000       465,000       187,000          --           --
Total liabilities..............   1,890,636     2,138,309       940,062     442,375      403,927
Redeemable preferred stock.....  $       --    $       --    $       --    $162,743    $      --
OPERATING DATA:
Revenues.......................  $  617,448    $  359,486    $  173,911    $116,908    $  92,387
Expenses.......................     465,675       262,173       134,041     106,646       90,427
Gain (loss) on sale of real
  estate assets................     131,034        (2,076)           --          --           --
Minority interest..............      40,737         7,469         2,368       1,519        3,417
Gain (loss) on interest rate
  swap.........................          --            --            99       4,278       (7,672)
Cumulative effect of a change
  in accounting principle......        (630)           --            --          --           --
Extraordinary loss.............      10,787         4,303            54       3,925        4,445
Net income (loss)..............  $  230,653    $   83,465    $   37,547    $  9,096    $ (13,574)
Net income (loss) per common
  share, Basic.................  $     1.76    $     0.80    $     0.63    $   0.19    $   (0.94)
Net income (loss) per common
  share, Diluted...............  $     1.74    $     0.80    $     0.63    $   0.19    $   (0.94)
Dividends declared per common
  share........................  $     0.90    $     1.50    $     1.04    $   1.20    $    1.16
OTHER DATA:
Cash Flow from:
  Operations...................  $  223,505    $  182,797    $   65,922    $ 34,522    $  20,036
  Investing....................      52,488      (823,082)     (462,837)    (57,259)    (135,527)
  Financing....................    (318,183)      677,424       306,842     129,800      110,725
  Funds From Operations(1).....  $  242,426    $  155,915    $   68,308    $ 34,719    $  21,424
</TABLE>

- ---------------
(1) Funds from Operations is a calculation which is defined by NAREIT and is not
    indicative of either net income or cash flow from operations as calculated
    in accordance with GAAP as a measure of performance or liquidity.

     EQUIVALENT PER SHARE DATA

     We have summarized below the per share information for our respective
companies on an historical basis, pro forma combined basis and pro forma
combined equivalent basis. The pro forma combined summary amounts are based on
the purchase method of accounting. The Cornerstone per share pro forma combined
equivalents are calculated by multiplying the pro forma combined per share
amounts by the exchange ratio of 0.7009. Cornerstone stockholders who receive
Equity Office common shares in the REIT merger will receive 0.7009 of an Equity
Office common share in exchange for each share of Cornerstone common stock. You
should note that, in 1999, Cornerstone declared distributions equal to $.90 per
share of Cornerstone common stock but paid distributions equal to $1.20 per
share of Cornerstone common stock during such period.

                                       17
<PAGE>   30

     The following information should be read together with the historical and
pro forma financial statements included or incorporated by reference in this
document. See "Where You Can Find More Information" on page 163.

<TABLE>
<CAPTION>
                                                              FOR THE YEAR ENDED
                                                              DECEMBER 31, 1999
                                                              ------------------
                                                              BASIC     DILUTED
                                                              ------    --------
<S>                                                           <C>       <C>
NET INCOME PER COMMON SHARE(1):
  Equity Office.............................................  $1.49      $1.48
  Cornerstone...............................................  $1.76      $1.74
  Equity Office and Cornerstone pro forma combined before
     extraordinary items and cumulative effect of a change
     in accounting principle................................  $1.78      $1.76
  Cornerstone pro forma combined equivalent.................  $1.25      $1.23
</TABLE>

- ---------------
(1) The net income per common share amounts include the gain on sales of real
    estate in 1999 for Equity Office and Cornerstone. Such gains can fluctuate
    substantially from year to year. Therefore, the following table reflects net
    income per share before extraordinary items, cumulative effect of a change
    in accounting principle and the gain on sales of real estate for Equity
    Office and Cornerstone, net of effect of minority interest:

<TABLE>
<CAPTION>
                                                              BASIC    DILUTED
                                                              -----    -------
<S>                                                           <C>      <C>
NET INCOME BEFORE EXTRAORDINARY ITEMS, CUMULATIVE EFFECT OF
  A CHANGE IN ACCOUNTING PRINCIPLE AND GAIN ON SALES OF REAL
  ESTATE PER COMMON SHARE, NET OF EFFECT OF MINORITY
  INTEREST:
  Equity Office.............................................  $1.32     $1.31
  Cornerstone...............................................  $0.96     $0.96
  Equity Office and Cornerstone pro forma combined..........  $1.23     $1.22
  Cornerstone pro forma combined equivalent.................  $0.86     $0.86
</TABLE>

<TABLE>
<CAPTION>
                                                              FOR THE YEAR ENDED
                                                                 DECEMBER 31,
                                                                     1999
                                                              ------------------
<S>                                                           <C>
CASH DISTRIBUTIONS DECLARED PER COMMON SHARE:
Equity Office...............................................       $   1.58
Cornerstone.................................................       $   0.90
Equity Office and Cornerstone pro forma combined............       $   1.58
Cornerstone pro forma combined equivalent...................       $   1.11
SHAREHOLDERS' EQUITY (BOOK VALUE) PER COMMON SHARE (END OF
  PERIOD):
Equity Office...............................................       $  24.69
Cornerstone.................................................       $  14.87
Equity Office and Cornerstone pro forma combined............       $  24.69
Cornerstone pro forma combined equivalent...................       $  17.31
</TABLE>

     MARKET PRICES OF EQUITY OFFICE COMMON SHARES AND CORNERSTONE COMMON STOCK

     The following table sets forth the price per share of Equity Office common
shares and Cornerstone common stock based on the last reported sale prices per
share on the NYSE on February 10, 2000, the last trading day prior to the public
announcement of the execution of the merger agreement, and on

                                       18
<PAGE>   31

, 2000, the most recent date for which prices are available prior to mailing
this consent solicitation/ information statement/prospectus.

<TABLE>
<CAPTION>
                                                                                PRICE PER SHARE
                                                                       ---------------------------------
                                                                                       CORNERSTONE PRO
                                                       EQUITY OFFICE   CORNERSTONE   FORMA EQUIVALENT(1)
                                                       -------------   -----------   -------------------
<S>                                                    <C>             <C>           <C>
February 10, 2000....................................    $25.6875        $14.875           $18.00
                 , 2000(2)...........................    $               $                 $
</TABLE>

- ---------------
(1) Computed by multiplying the Equity Office common share closing price by the
    0.7009 exchange ratio.

(2) The average last reported sale price per Equity Office common share for the
    five trading days preceding                , 2000 was $          . The
    Cornerstone pro forma equivalent, based on such five trading days, would be
    $          .

REIT MERGER SELECTED UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL DATA

     The following table sets forth the summary unaudited pro forma combined
financial data for Equity Office and Cornerstone as a combined entity, giving
effect to the REIT merger as if it had occurred on the dates indicated herein
and after giving effect to the pro forma adjustments. The unaudited pro forma
combined operating data are presented as if the REIT merger had been consummated
on January 1, 1999. The unaudited pro forma combined balance sheet data at
December 31, 1999 is presented as if the REIT merger had occurred on December
31, 1999. In the opinion of management of Equity Office, all adjustments
necessary to reflect the effects of these transactions have been made. The REIT
merger will be accounted for under the purchase method of accounting in
accordance with Accounting Principles Board Opinion No. 16.

     The pro forma financial information should be read in conjunction with, and
is qualified in its entirety by, the respective historical audited financial
statements and financial statement notes of Equity Office and of Cornerstone
incorporated by reference into this consent solicitation/information
statement/prospectus. The unaudited pro forma operating data are presented for
comparative purposes only and are not necessarily indicative of what the actual
combined results of operations of Equity Office and Cornerstone would have been
for the period presented, nor does such data purport to represent the results of
future periods. See "Equity Office Pro Forma Condensed Combined Financial
Statements" on page F-10.

<TABLE>
<CAPTION>
                                                                          PRO FORMA
                                                                     FOR THE YEAR ENDED
                                                                      DECEMBER 31, 1999
                                                              ---------------------------------
                                                                   (DOLLARS IN THOUSANDS,
                                                                   EXCEPT PER SHARE DATA)
<S>                                                           <C>
OPERATING DATA:
Revenues:
  Rental....................................................            $  1,954,581
  Tenant reimbursements.....................................                 402,743
  Parking...................................................                 139,547
  Other.....................................................                  38,028
  Fee income................................................                  11,616
  Interest/dividends........................................                  18,459
                                                                        ------------
          Total revenues....................................               2,564,974
                                                                        ------------
</TABLE>

                                       19
<PAGE>   32

<TABLE>
<CAPTION>
                                                                          PRO FORMA
                                                                     FOR THE YEAR ENDED
                                                                      DECEMBER 31, 1999
                                                              ---------------------------------
                                                                   (DOLLARS IN THOUSANDS,
                                                                   EXCEPT PER SHARE DATA)
<S>                                                           <C>
Expenses:
  Interest:
     Expense incurred.......................................                 639,859
     Amortization of deferred financing costs...............                  10,366
  Depreciation..............................................                 442,831
  Amortization..............................................                  14,545
  Real estate taxes.........................................                 315,332
  Insurance.................................................                  13,137
  Repairs and maintenance...................................                 284,358
  Property operating........................................                 252,826
  Ground rent...............................................                   8,294
  General and administrative................................                 107,933
                                                                        ------------
          Total expenses....................................               2,089,481
                                                                        ------------
Income before allocation to minority interests, income from
  investment in unconsolidated joint ventures and net gain
  on sales of real estate...................................                 475,493
Minority interests:
  EOP Partnership...........................................                 (81,148)
  Partially owned properties................................                  (7,736)
Income from investment in unconsolidated joint ventures.....                  14,546
Net gain on sales of real estate............................                 190,695
                                                                        ------------
Net income from continuing operations.......................                 591,850
Put option settlement.......................................                  (5,658)
Preferred distributions.....................................                 (43,603)
                                                                        ------------
Net income from continuing operations before extraordinary
  items and cumulative effect of a change in accounting
  principle available for common shares.....................            $    542,589
                                                                        ============
Net income from continuing operations before extraordinary
  items and cumulative effect of a change in accounting
  principle per weighted average common share
  outstanding -- basic......................................            $       1.78
                                                                        ============
Weighted average common shares outstanding -- basic.........             305,424,355
                                                                        ============
Net income from continuing operations before extraordinary
  items and cumulative effect of a change in accounting
  principle per weighted average common share
  outstanding -- diluted....................................            $       1.76
                                                                        ============
Weighted average common shares outstanding -- diluted.......             354,965,413
                                                                        ============
BALANCE SHEET DATA (AT END OF PERIOD):
  Investment in real estate net of accumulated
     depreciation...........................................            $ 16,848,787
                                                                        ============
  Total assets..............................................            $ 18,659,040
                                                                        ============
  Total debt................................................            $  8,779,344
                                                                        ============
  Total liabilities.........................................            $  9,377,262
                                                                        ============
  Minority interests........................................            $  1,237,032
                                                                        ============
  Shareholders' equity......................................            $  8,044,746
                                                                        ============
</TABLE>

                                       20
<PAGE>   33

                                  RISK FACTORS

     In addition to the risks relating to the businesses of Equity Office, EOP
Partnership and Cornerstone, which are incorporated by reference in this
document from other SEC filings, and the other information included in this
document, including the matters addressed in "A Warning About Forward-Looking
Statements," Cornerstone Partnership unitholders should carefully consider the
following risk factors relating to the mergers in determining whether or not to
vote in favor of the approval of the partnership merger and the REIT merger and
whether or not to redeem your Cornerstone Partnership units for Cornerstone
common stock and thereby participate in the REIT merger.

YOU MAY RECEIVE EOP PARTNERSHIP CLASS A UNITS IN THE PARTNERSHIP MERGER, OR, IF
YOU REDEEM YOUR CORNERSTONE PARTNERSHIP UNITS BEFORE THE PARTNERSHIP MERGER,
EQUITY OFFICE COMMON SHARES IN THE REIT MERGER, WITH A VALUE OF LESS THAN $18.00
PER UNIT OR $18.00 PER SHARE

     There can be no assurance that any EOP Partnership units you receive in the
partnership merger or, if you redeem your Cornerstone Partnership units before
the partnership merger, any Equity Office common shares you receive in the REIT
merger, will have a redemption value, or trade at a price, in the case of Equity
Office common shares, equal to $18.00, the cash price, on a per unit or per
share equivalent basis at the time of or following the mergers. Each EOP
Partnership unit to be received by Cornerstone Partnership unitholders in the
partnership merger will be redeemable following the partnership merger for one
Equity Office common share or its cash equivalent, at Equity Office's option.
Consequently, the redemption value of the EOP Partnership units you receive in
the partnership merger will be directly affected by price fluctuations of the
Equity Office common shares through the closing of the mergers and thereafter.
The redemption value of the EOP Partnership units and the Cornerstone
Partnership units, as reflected in the relative market prices of the Equity
Office common shares and the shares of Cornerstone common stock, may vary
significantly from the redemption value as reflected in such prices as of the
date of execution of the merger agreement, the date of this document or the date
the mergers are completed. Similarly, any Equity Office common shares you
receive in the REIT merger, if you elect to redeem your Cornerstone Partnership
units before the partnership merger, may vary significantly from the current
market value.

     The exchange ratios for Cornerstone Partnership units to be converted into
EOP partnership units in the partnership merger and for shares of Cornerstone
common stock to be converted into Equity Office common shares in the REIT merger
were fixed at the time of the signing of the merger agreement and are not
subject to adjustment based on changes in the trading price of Equity Office
common shares or Cornerstone common stock before the closing of the merger.
Accordingly, the redemption value of the EOP Partnership units you receive in
the partnership merger, and the market value of any Equity Office common shares
that you receive in the REIT merger, if you redeem your Cornerstone Partnership
units prior to the partnership merger, will depend on the market value of Equity
Office common shares at the time of completion of the mergers.

THE DIRECTORS AND OFFICERS OF CORNERSTONE MAY HAVE INTERESTS IN THE COMPLETION
OF THE MERGERS THAT ARE DIFFERENT FROM THE INTERESTS CORNERSTONE PARTNERSHIP'S
UNITHOLDERS AND CORNERSTONE'S STOCKHOLDERS

     In considering the recommendation of the Cornerstone board with respect to
the partnership merger, Cornerstone unitholders should be aware that, as
described below, certain Cornerstone directors and officers and PGGM have
interests in the mergers that differ from, or are in addition to, the interests
of Cornerstone Partnership unitholders and Cornerstone stockholders generally.

     Trustees of Equity Office After the Merger.  Following the merger, the
current trustees of Equity Office will remain as trustees of the combined
entity. In addition, three current directors of Cornerstone, John S. Moody, Jan
H.W.R. van der Vlist and William Wilson III, will become trustees of Equity
Office, with their terms expiring in 2002, 2003 and 2003, respectively. Under
the terms of the merger agreement, Equity Office is obligated to nominate Mr.
van der Vlist for reelection to the board of trustees in 2003 and 2006 if PGGM
and its affiliates continue to own at least 21,000,000 of the issued and
outstanding Equity

                                       21
<PAGE>   34

Office common shares, as adjusted for share splits or similar actions, at all
times up to the time the trustees are being elected in those years. If Mr. van
der Vlist fails to stand for reelection in 2003 or 2006 for any reason, or in
the event of his death or earlier resignation, and if PGGM continues to own at
least 21,000,000 of the issued and outstanding Equity Office shares as described
above, Equity Office is required to take all action necessary to nominate a
replacement designated by PGGM for election or reelection as a trustee for an
additional three-year term, subject to Equity Office's approval if the
replacement is not an officer, director or employee of PGGM.

     Equity-Based Awards.  Under Cornerstone's incentive stock plans, an
aggregate of 89,113 unvested shares of restricted common stock previously
awarded to the executives who are parties to the retention agreements described
below will vest in full upon completion of the mergers and will be converted
into cash or common shares of Equity Office according to the terms of the merger
agreement. In addition, unvested options to purchase an aggregate of 3,177,476
shares of Cornerstone common stock previously awarded to such executives will
vest in full upon completion of the mergers, and each option may be surrendered
within two business days following the REIT merger by the holder of the option
to Equity Office for cash equal to the difference between $18.00 per share and
the exercise price of the option or exchanged for options to purchase common
shares of Equity Office according to the terms of the merger agreement.
Cornerstone and Equity Office have agreed that the REIT merger will constitute a
change in control for purposes of all applicable Cornerstone benefit and
compensation plans, including the Cornerstone 1998 Long Term Incentive Plan and
all stock option and restricted stock agreements provided under the terms of
such plans.

     Mr. Moody has agreed with Cornerstone to waive the acceleration of his
unvested restricted stock and unvested stock options.

     Moody Agreement.  Cornerstone has entered into a contract with Mr. Moody
whereby amounts are accrued under an unfunded arrangement to pay Mr. Moody a
supplemental pension. Under the contract, his supplemental pension account was
established with a credit of $250,000 as of July 1, 1995, and Cornerstone is
obligated to credit the account in the amount of $60,000 each subsequent July 1
during the continuance of Mr. Moody's employment.

     The account is also credited with any deemed income, gains or losses which
would be attributable to a corresponding investment of an equal cash amount in
such investment as Cornerstone, taking into account Mr. Moody's views, shall
deem the account to be invested. Payment of Mr. Moody's supplemental pension
account is to be made in a lump sum as of the date Mr. Moody terminates his
employment. However, if his employment is terminated for cause, Mr. Moody will
forfeit the account and no payment will be made. The contract also provides
that, outside of a change in control context, if Mr. Moody's employment
terminates for a reason other than cause, an additional credit of $60,000 (or
less, if Mr. Moody resigns without good reason) will be made to the account.
Following a change in control, in the event Mr. Moody's employment is terminated
by Cornerstone other than for cause, or if he resigns for good reason,
Cornerstone is obligated to credit his supplemental pension account with an
amount equal to $60,000 times the number of years, including fractional portions
of a year, remaining between his age on the date his employment ceases and age
60.

     Retention Agreements.  Cornerstone has entered into retention agreements
with some of its officers to address the terms and conditions of their
employment in the event of a change in control. A "change in control" generally
is said to occur when: (a) any person becomes the owner of 25% or more of
Cornerstone's voting securities; (b) directors who constitute the Cornerstone
board at the beginning of any two-year period, and any new directors whose
election or nomination for election was approved by a vote of at least three
quarters of the directors then in office who either were directors at the
beginning of such period or whose election or nomination for election was
previously so approved, cease to constitute a majority; (c) a merger,
consolidation or reorganization in which Cornerstone's voting securities do not
continue to represent at least 50% of the surviving entity; or (d) a
reorganization, liquidation, or sale of all or substantially all of
Cornerstone's assets.

                                       22
<PAGE>   35

     In the event of termination of employment by Cornerstone without cause, or
by the employee for good reason, within two years following a change in control,
Cornerstone will make a lump sum payment of: (a) the pro rata portion of the
annual bonus for the year termination occurred, calculated on the basis of the
target bonus and on the assumption that all performance goals have been or will
be achieved; and (b) three times annual compensation in the case of Messrs.
Wilson and Moody and H. Lee Van Boven and Rodney C. Dimock, and two times annual
compensation in the case of all other officers. Annual compensation generally is
defined as the salary in effect immediately before termination or change in
control, plus the highest of the target annual bonus for the termination year or
the average of the three annual bonuses paid immediately prior to the
termination or the change in control.

     An officer may be terminated for "cause" if he or she is convicted of a
felony, reveals confidential information about Cornerstone or refuses to
substantially perform his duties. An officer can terminate for "good reason" if
Cornerstone reduces his salary or bonus target, reduces the value of employee
benefits materially, relocates his office more then 25 miles from the present
location, detrimentally alters his title or position, fails to get a successor
to agree to assume the obligations under the retention agreement or materially
breaches any provision of the agreement.

     In addition, the officer and his eligible dependents will continue to be
eligible to participate during the benefit continuation period in the medical,
dental, health, life and other welfare benefit plans and arrangements applicable
to him immediately before his or her termination of employment, on the same
terms and conditions in effect immediately before such termination. "Benefit
continuation period" means the period beginning on the day of termination and
ending on the earlier to occur of: (a) the third anniversary of the date of
termination in the case of Messrs. Wilson, Moody, Van Boven and Dimock and the
second anniversary of the date of termination in the case of all other officers;
and (b) the date that the officer is eligible and elects coverage under the
plans of a subsequent employer which provide substantially equivalent or greater
benefits to the officer and his dependents.

     If the payments to an officer under the retention agreement constitute
"parachute payments," as defined in section 280G of the Internal Revenue Code,
and the officer would receive more value after taxes if the payments to be made
to the officer were capped at three times the "base amount" less $1.00, then the
payments will be reduced to that amount.

     Equity Office has agreed to assume and to perform Cornerstone's obligations
under the retention agreements in the same manner and to the same extent that
Cornerstone would be required to perform such obligations if the merger had not
taken place. The parties have agreed that the merger will be a "change in
control" for purposes of the retention agreements.

     Mr. Moody has agreed to waive any rights to payment of the lump sum payment
and to the continuation of benefits under his retention agreement in
consideration of Cornerstone's payment to Mr. Moody upon completion of the
merger, in recognition of his past service to Cornerstone, of $7.3 million or,
if the merger is completed on or after July 1, 2000, $6.8 million. Messrs. Van
Boven and Dimock have each agreed to waive the payment of $1.0 million, and R.
Matthew Moran has agreed to waive the payment of $500,000, of the lump sum
payment otherwise payable to each of them in the event of the termination of
their employment other than for cause after the merger.

     Noncompetition Agreements.  Each of Messrs. Moody, Van Boven, Dimock and
Moran have agreed to enter into noncompetition agreements with Equity Office
that will restrict their ability to engage in business activities that are
competitive with those of Equity Office after the mergers. In order to induce
Messrs. Moody, Van Boven, Dimock and Moran to enter into such agreements, Equity
Office will pay $5,000,000 to Mr. Moody, $1,000,000 to each of Messrs. Van Boven
and Dimock and $500,000 to Mr. Moran upon the completion of the merger.

     Escrowed Units.  In connection with the acquisition of William Wilson &
Associates in December 1998, an aggregate of 387,137 partnership units issued by
the Cornerstone Partnership that would have been distributable to the general
partners or managers of the four Wilson-sponsored opportunity funds acquired by
Cornerstone in the transaction were placed in escrow pursuant to an agreement
with certain

                                       23
<PAGE>   36

investors in the opportunity funds. These units would have been distributed to
these general partners and managers under the governing instruments of the
opportunity funds if the units were valued at $17.25 per unit, the agreed-upon
value of the Cornerstone shares and units issued in the Wilson transaction. The
units were placed in escrow pending a determination of their value during the
one-year period beginning on the date the units were released from the lockup
provisions applicable to the units issued in the Wilson acquisition. Mr. Wilson
and other executives of Cornerstone indirectly beneficially own in the aggregate
319,369 of such escrowed units.

THE FAILURE OF CORNERSTONE PARTNERSHIP UNITHOLDERS AND CORNERSTONE STOCKHOLDERS
TO APPROVE THE MERGER AGREEMENT MAY REQUIRE, UNDER LIMITED CIRCUMSTANCES,
CORNERSTONE PARTNERSHIP TO PAY TERMINATION FEES AND MAY RESULT IN A DECREASE IN
THE MARKET PRICE OF CORNERSTONE COMMON STOCK

     If the Cornerstone Partnership unitholders and the Cornerstone common and
preferred stockholders fail to approve the merger agreement, or if the mergers
are not completed for any reason, Cornerstone and Cornerstone Partnership may be
subject to material risks, including the risk that, under limited circumstances,
Cornerstone Partnership pay up to $100 million in termination fees and expenses
to EOP Partnership, which could lead to a possible decline in the market price
of Cornerstone common stock to the extent current market prices reflect a market
assumption that the mergers will be completed. For a more detailed discussion on
termination fees and expenses, see "The Merger Agreement -- Expenses;
Termination Fee" on page 68.

     If, following termination of the merger agreement, the Cornerstone board of
directors determines to seek another merger or business combination, there can
be no assurance that it will be able to find a partner willing to pay an
equivalent or more attractive price than would be provided by Equity Office and
EOP Partnership in the mergers. Under the terms of the merger agreement, before
the termination of the merger agreement, Cornerstone and Cornerstone Partnership
are not permitted to:

     - invite, initiate, solicit or encourage any alternative acquisition
       proposal;

     - except in circumstances expressly permitted under the merger agreement,
       engage in any discussions or negotiations with, or provide any
       confidential or non-public information or data to, any person relating
       to, or that may reasonably be expected to lead to, an alternative
       acquisition proposal;

     - enter into any letter of intent, agreement in principle or agreement
       relating to an alternative acquisition proposal; or

     - publicly propose to agree to do any of the foregoing or otherwise
       facilitate any effort or attempt to make or implement an alternative
       acquisition proposal. See "The Merger Agreement -- No Solicitation by
       Cornerstone or Cornerstone Partnership" on page 65.

IF THE AGGREGATE FAIR MARKET VALUE OF THE EQUITY OFFICE COMMON SHARES TO BE
ISSUED IN THE REIT MERGER DOES NOT REPRESENT AT LEAST 40% OF THE REIT MERGER
CONSIDERATION TO BE PAID AT THE TIME OF THE CLOSING OF THE REIT MERGER, LEGAL
OPINIONS REQUIRED TO BE DELIVERED FOR THE REIT MERGER TO BE COMPLETED COULD NOT
BE DELIVERED, IN WHICH CASE THE MERGERS WOULD NOT BE COMPLETED AND THE MARKET
PRICE OF CORNERSTONE COMMON STOCK COULD DECLINE AS A RESULT

     It is a condition to the consummation of the mergers that Hogan & Hartson
L.L.P., counsel to Equity Office, and King & Spalding, counsel to Cornerstone,
deliver opinions that the REIT merger qualifies as a reorganization under
section 368(a) of the Internal Revenue Code. The required tax opinions will not
be delivered, and the mergers will not be consummated, unless the aggregate fair
market value of the Equity Office common shares issued in the REIT merger
represents at least 40% of the aggregate value of the total consideration issued
by Equity Office in the REIT merger, as of the closing of the REIT merger and
taking into account any cash paid for fractional Equity Office common shares.
For example, if the REIT merger had occurred on                , 2000, then
based on the trading price of Equity Office common shares on that date and the
number of shares of Cornerstone common stock issued and outstanding on that
date, assuming that no holders of Cornerstone Partnership units had converted
their units into Cornerstone

                                       24
<PAGE>   37

common stock immediately before the REIT merger, the aggregate fair market value
of the Equity Office common shares that would have been issued in the REIT
merger would represent approximately      % of the value of the total
consideration paid by Equity Office in the REIT merger. There is no guarantee,
however, that the trading price of the Equity Office common shares will be high
enough at the scheduled closing of the REIT merger to allow counsel to render
the required tax opinions and the mergers to be consummated.

EQUITY OFFICE AND CORNERSTONE MAY NOT BE SUCCESSFULLY INTEGRATED AND INTENDED
BENEFITS OF THE MERGERS MAY NOT BE REALIZED, WHICH COULD HAVE A NEGATIVE IMPACT
ON THE MARKET PRICE OF EQUITY OFFICE COMMON SHARES AND THE VALUE OF THE EOP
PARTNERSHIP UNITS AFTER COMPLETION OF THE MERGERS

     The completion of the mergers poses risks for the ongoing operations of
Equity Office and EOP Partnership, including that:

     - following the mergers, Equity Office and EOP Partnership may not achieve
       the expected cost savings and operating efficiencies;

     - the Cornerstone portfolio may not perform as well as Equity Office
       anticipates;

     - Equity Office and EOP Partnership may experience difficulties and incur
       expenses associated with the assimilation and retention of Cornerstone
       non-executive employees; and

     - Equity Office and EOP Partnership may not effectively integrate the
       operations of Cornerstone and Cornerstone Partnership.

     If Equity Office and EOP Partnership fail to successfully integrate
Cornerstone and Cornerstone Partnership and/or fail to realize intended benefits
of the mergers due to any of the foregoing reasons, the market price of Equity
Office common shares and the value of EOP Partnership units could decline from
their market price and redemption value, as applicable, at the time of
completion of the mergers.

THERE IS NO PUBLIC MARKET FOR EOP PARTNERSHIP UNITS AND NONE IS EXPECTED TO
DEVELOP, WHICH MAY CAUSE SOME DIFFICULTY IN SELLING ANY EOP PARTNERSHIP UNITS
YOU RECEIVE IN THE PARTNERSHIP MERGER

     There is no public market for EOP Partnership units and none is expected to
develop. However, the partnership agreement of EOP Partnership provides that
unitholders may, subject to specified limitations, redeem their EOP Partnership
units for Equity Office common shares on a one-on-one basis or their cash
equivalent, at the election of Equity Office. The determination of whether the
redeeming party receives cash or Equity Office common shares is within the sole
discretion of Equity Office. If you are unable to redeem your EOP Partnership
units, you may have difficulty selling those units because of the lack of a
public market and the restrictions on transfer contained in the partnership
agreement of EOP Partnership..

                                       25
<PAGE>   38

                   A WARNING ABOUT FORWARD-LOOKING STATEMENTS

     Equity Office, EOP Partnership, Cornerstone and Cornerstone Partnership
have each made forward-looking statements in this document, and in documents
that are incorporated by reference in this document, that are subject to risks
and uncertainties. Forward-looking statements include the information concerning
possible or assumed future results of operations of Equity Office, EOP
Partnership, Cornerstone and Cornerstone Partnership. Also, statements including
words such as "believes," "expects," "anticipates," "intends," "plans,"
"estimates," or similar expressions are forward-looking statements. Many
factors, some of which are discussed elsewhere in this document and in the
documents incorporated by reference in this document, could affect the future
financial results of Equity Office and EOP Partnership and could cause actual
results to differ materially from those expressed in forward-looking statements
contained or incorporated by reference in this document. Important factors that
could cause actual results to differ materially from the expectations reflected
in the forward-looking statements in this consent solicitation/information
statement/prospectus include, among others, the factors discussed under the
caption "Risk Factors" on page 21 and "Risk Factors" in the Form 10-Ks of Equity
Office and EOP Partnership incorporated herein by reference, changes of a
macroeconomic nature, including changes in the economic conditions affecting
industries in which Equity Office's principal tenants compete, the ability to
timely lease or re-lease square footage at current or anticipated rents, the
ability to achieve economies of scale over time, the demand for tenant services
beyond those traditionally provided by landlords, changes in interest rates,
changes in operating costs, future demand for Equity Office's or EOP
Partnership's debt and equity securities and the ability to complete current and
future development projects on time and on schedule.

     Forward-looking statements are not guarantees of performance. They involve
risks, uncertainties and assumptions. The future results and shareholder values
of Equity Office following completion of the REIT merger and unitholder values
of EOP Partnership following completion of the partnership merger may differ
materially from those expressed in these forward-looking statements. Many of the
factors that will determine these results and values are beyond Equity Office's,
EOP Partnership's, Cornerstone's and Cornerstone Partnership's ability to
control or predict. For those statements, Equity Office, EOP Partnership,
Cornerstone and Cornerstone Partnership claim the protection of the safe harbor
for forward-looking statements contained in the Private Securities Litigation
Reform Act of 1995.

INFORMATION ABOUT THE ACTIONS TAKEN OR TO BE TAKEN BY THE GENERAL PARTNER OF EOP
                                  PARTNERSHIP

     Under the authority granted in the partnership agreement of EOP
Partnership, Equity Office, as the general partner of EOP Partnership, has
determined that the partnership merger is in the best interests of EOP
Partnership and its unitholders, and has approved the merger agreement and the
partnership merger. No vote or consent of unitholders of EOP Partnership is
required under the partnership agreement of EOP Partnership for approval of the
partnership merger.

     The partnership agreement of EOP Partnership requires the approval of the
REIT merger by the consent of unitholders holding at least a majority of the
outstanding EOP Partnership units, including any EOP Partnership units held by
Equity Office. As of                , 2000, Equity Office owned approximately
88.2% of the outstanding EOP Partnership units and intends to take action by
written consent, as permitted under the partnership agreement of EOP
Partnership, to approve the REIT Merger on or about                , 2000.
Because Equity Office owns more than a majority of the outstanding partnership
units of EOP Partnership, no vote or consent of unitholders of EOP Partnership,
other than Equity Office, is required for approval of the REIT merger, and none
is being solicited. Accordingly, under applicable SEC rules, this document is
being forwarded to unitholders of EOP Partnership of record on           , 2000
for informational purposes only.

                                       26
<PAGE>   39

                  CORNERSTONE PARTNERSHIP CONSENT SOLICITATION

PURPOSE OF THE CONSENT SOLICITATION

     Cornerstone is asking Cornerstone Partnership unitholders to consent to the
mergers. The partnership agreement of Cornerstone Partnership requires the
approval of the mergers by the consent of unitholders holding at least a
majority of the outstanding Cornerstone Partnership units, including any
Cornerstone Partnership units held by Cornerstone. As of                , 2000,
Cornerstone owned approximately 87.1% of the Cornerstone Partnership units.
Cornerstone is required to vote its units in proportion to the manner in which
all outstanding shares of capital stock of Cornerstone are voted at the special
meeting of stockholders of Cornerstone to be held on                , 2000 in
connection with the REIT merger. You may execute a consent to the mergers if you
owned Cornerstone Partnership units on             , 2000.

WHO CAN CONSENT

     You are entitled to consent with respect to your Cornerstone Partnership
units if our records showed that you held your Cornerstone Partnership units as
of the close of business on             , 2000. At the close of business on that
date, a total of 148,852,333 Cornerstone Partnership units were outstanding and
entitled to consent. Each Cornerstone Partnership unit represents one vote. The
enclosed consent form shows the number of Cornerstone Partnership units for
which you are entitled to consent. Your individual consent is confidential and
will not be disclosed to third parties, other than Equity Office.

CONSENT, REDEMPTION AND ELECTION PROCEDURES

     Consent Forms. To consent, simply mark your consent form, sign and date it,
and return it in the postage-paid envelope provided.

     Redemption of Cornerstone Partnership Units. You may elect to redeem your
Cornerstone Partnership units under one of two methods. First, you may exercise
any unit redemption right that you currently have under the partnership
agreement of Cornerstone Partnership at any time before the partnership merger.
Any exercise by you of your unit redemption right under the partnership
agreement of Cornerstone Partnership will not be conditioned on completion of
the mergers. By exercising your unit redemption right under the partnership
agreement of Cornerstone Partnership, you would not receive units of EOP
Partnership in the partnership merger, but instead would participate in the REIT
merger on the same basis as other common stockholders of Cornerstone. Generally,
a Cornerstone Partnership unit is redeemable on a one-for-one basis for a share
of Cornerstone common stock commencing one year after the date it was first
issued. Accordingly, if you received your Cornerstone Partnership units less
than one year ago, you may not have a currently exercisable unit redemption
right under the partnership agreement of Cornerstone Partnership.

     Alternatively, under the merger agreement, you have the right to redeem
some or all of your Cornerstone Partnership units for Cornerstone common stock
on a one-for-one basis, whether or not you have a currently exercisable right to
redeem your units under the partnership agreement of Cornerstone Partnership.
The exercise by you of the unit redemption right under the merger agreement will
be effective only if the partnership merger is completed. Under the merger
agreement, you also may condition your redemption of units on the ability to
receive in the REIT merger only cash for some or all of the Cornerstone common
stock that you would receive upon redemption of your Cornerstone Partnership
units.

     Conditioning Your Redemption. In the REIT merger, Cornerstone common
stockholders may elect to receive for some or all of their shares of Cornerstone
common stock either $18.00 per share in cash, without interest, or 0.7009 of a
common share of Equity Office, subject to proration if either the cash election
or the share election is oversubscribed.

     If you redeem some or all of your Cornerstone Partnership units for
Cornerstone common stock under the provisions of the partnership agreement of
Cornerstone Partnership, or you elect to redeem some or all of your Cornerstone
Partnership units for Cornerstone common stock under the merger agreement, but
do

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<PAGE>   40

not condition the redemption on receiving cash in the REIT merger for the
Cornerstone common stock to be issued to you upon redemption, you will
participate in the REIT merger on the same basis as any other Cornerstone common
stockholder.

     If you condition your unit redemption under the merger agreement on the
ability to receive only cash in the REIT merger for some or all of your
Cornerstone Partnership units, you will receive in the REIT merger $18.00 in
cash per share of Cornerstone common stock received by you in the redemption
only if the cash condition is met. The cash condition will not be met if there
is an oversubscription of cash by all Cornerstone common stockholders, taking
into account cash elections made by all redeeming Cornerstone Partnership
unitholders. However, if there is an undersubscription of cash, taking into
account cash elections made by all Cornerstone common stockholders, but not
including cash elections made by Cornerstone Partnership unitholders who
conditioned their unit redemptions on the ability to receive cash in the REIT
merger, you may nevertheless have the opportunity to have your units redeemed
for Cornerstone common stock and receive cash in the REIT merger if the cash
consideration available after giving effect to cash elections made by the
Cornerstone common stockholders is sufficient to meet your specified cash
condition and your conditional cash redemption is chosen by lot from among other
conditional cash redemptions that were not initially satisfied. See "The Merger
Agreement -- The Partnership Merger" on page 53 and "The Merger Agreement -- The
REIT Merger" on page 53 for a more complete discussion of how proration in the
REIT merger might affect the consideration you will receive as a result of your
redemption of Cornerstone Partnership units.

     Notice of Redemption/Form of Election. In addition to the consent form, a
notice of redemption/form of election will be mailed to each holder of
Cornerstone Partnership units. In order to be effective, a notice of
redemption/form of election must be properly completed, signed and submitted to
the exchange agent listed in the instructions to the notice of redemption/form
of election at least two business days prior to the date of Cornerstone
stockholders special meeting, which is currently scheduled to occur on      ,
2000. You will be notified if the date of the Cornerstone stockholders special
meeting is moved. If you do not submit a properly completed notice of
redemption/form of election which is received by the exchange agent at least two
business days prior to the Cornerstone stockholders special meeting at the
address provided in the instructions to the notice of redemption/form of
election, then you will be deemed not to have redeemed your Cornerstone
Partnership units and each of such units will be converted in the partnership
merger into 0.7009 of an EOP Partnership unit.

     If you properly complete, sign and submit a notice of redemption/form of
election to the exchange agent and the mergers are completed, each share of
Cornerstone common stock issued in redemption of the Cornerstone Partnership
units covered by the notice of redemption will be exchanged for the merger
consideration as indicated on the form of election in accordance with the merger
agreement, any applicable portion, and your conditional redemption election.

     EQUITY OFFICE AND CORNERSTONE INTEND TO COMPLETE THE MERGERS IMMEDIATELY
AFTER THE SPECIAL MEETINGS FOR EQUITY OFFICE SHAREHOLDERS AND CORNERSTONE
STOCKHOLDERS, RESPECTIVELY. SUCH COMPLETION, HOWEVER, COULD BE DELAYED BY EQUITY
OFFICE AND CORNERSTONE IN ORDER THAT OTHER CLOSING CONDITIONS CAN BE SATISFIED.
ACCORDINGLY, ONCE A NOTICE OF REDEMPTION/FORM OF ELECTION HAS BEEN DELIVERED, A
CORNERSTONE PARTNERSHIP UNITHOLDER WILL BE UNABLE TO SELL, OR OTHERWISE
TRANSFER, SUCH UNITHOLDER'S UNITS FOR AN INDEFINITE PERIOD OF TIME.

REQUIRED VOTE

     Approval of the mergers requires the affirmative consent of the holders of
a majority of the Cornerstone Partnership units. Cornerstone is required to vote
its units in proportion to the manner in which all outstanding shares of capital
stock of Cornerstone are voted at the special meeting of stockholders of
Cornerstone to be held on             , 2000 in connection with the REIT merger.

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<PAGE>   41

HOW YOU MAY REVOKE YOUR NOTICE OF REDEMPTION

     If you conditionally elect to redeem some or all of your Cornerstone
Partnership units under the merger agreement, you can revoke or amend your
notice of redemption at any time before 5:00 p.m., Eastern Time, two business
days prior to the Cornerstone stockholders special meeting, by submitting
written notice to Cornerstone Partnership, with copies to Cornerstone and the
exchange agent, which must receive the notice at or before that time. A notice
of redemption under the provisions of the merger agreement is conditioned on the
completion of the partnership merger and, if you choose, can be conditioned on
the ability to receive only cash for some or all of the shares of Cornerstone
common stock that would be received in the redemption.

     A notice of redemption made under the provisions of the partnership
agreement of Cornerstone Partnership is not revocable and may not be conditioned
on completion of the partnership merger or the ability to receive cash in the
REIT merger.

HOW YOU MAY REVOKE YOUR CONSENT OR FORM OF ELECTION

     Revocation of a Consent Form. To revoke your consent form, you must (a) so
advise Cornerstone's secretary, Thomas P. Loftus, c/o Cornerstone Properties
Inc., 126 East 56th Street, New York, New York 10022, in writing received before
            , 2000 or (b) deliver to Mr. Loftus before             , 2000 a
consent form dated after your initial consent form.

     Revocation of an Election. You may change your cash or share election or
revoke it at any time before 5:00 p.m., Eastern Time, two business days prior to
the Cornerstone stockholders special meeting, by submitting written notice to
the exchange agent, with a copy to Cornerstone Partnership, which must receive
the notice at or before that time.

COST OF THIS CONSENT SOLICITATION

     Cornerstone Partnership will pay the cost of its consent solicitation. In
addition to soliciting consent forms by mail, we expect that certain of our
officers or other representatives of Cornerstone Partnership or its general
partner, Cornerstone, will solicit Cornerstone Partnership unitholders
personally and by telephone. None of these employees or representatives will
receive any additional or special compensation for doing this. We will, upon
request, reimburse nominees, if any, for their reasonable expenses in sending
consent material to their principals and obtaining their consent.

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<PAGE>   42

                             THE PARTNERSHIP MERGER

STRUCTURE OF THE MERGERS; PARTNERSHIP MERGER EXCHANGE RATIO

     The merger agreement contemplates the following two-step transaction:

     - the partnership merger, whereby Cornerstone Partnership will merge with
       and into EOP Partnership and Cornerstone Partnership will cease to exist;
       followed by

     - the REIT merger, whereby Cornerstone will merge with and into Equity
       Office and Cornerstone will cease to exist.

     In the partnership merger, holders of class A common units of limited
partnership interest in Cornerstone Partnership, including Cornerstone, who have
not elected to redeem their units for shares of Cornerstone common stock, will
receive, for each class A common unit issued and outstanding immediately before
the partnership merger, 0.7009 of a class A unit of limited partnership interest
in EOP Partnership, rounded to the nearest whole unit.

REDEMPTION OF CORNERSTONE PARTNERSHIP UNITS; PARTICIPATION IN CASH/SHARE
ELECTION

     The merger agreement provides that, before the partnership merger,
Cornerstone Partnership unitholders, other than Cornerstone, will have the right
to have all or any portion of their Cornerstone Partnership units redeemed by
Cornerstone for shares of Cornerstone common stock and to participate in the
REIT merger as stockholders of Cornerstone. These redemptions will be
conditioned upon the completion of the partnership merger. In addition,
Cornerstone Partnership unitholders who exercise this redemption right will be
able to condition their redemption of all units upon the ability to receive in
the REIT merger only cash in exchange for some or all of the Cornerstone common
stock that would be issued in the redemption. Cornerstone Partnership
unitholders may also exercise any presently exercisable redemption right they
have under the partnership agreement of Cornerstone Partnership and thereby
participate in the REIT merger as stockholders of Cornerstone.

     The merger agreement also provides that the former Cornerstone Partnership
unitholders, other than Cornerstone, will have the right, beginning immediately
after the partnership merger, to redeem the EOP Partnership class A units issued
to them in the partnership merger under the partnership agreement of EOP
Partnership. Upon redemption of these units, these unitholders would receive
Equity Office common shares on a one-for-one basis or their cash equivalent, at
the election of Equity Office, on the same basis as other limited partners of
EOP Partnership.

BACKGROUND OF THE PARTNERSHIP MERGER AND THE REIT MERGER

     In pursuing their strategies for enhancing unitholder and shareholder
value, each of Equity Office, EOP Partnership, Cornerstone and Cornerstone
Partnership regularly consider opportunities for acquisitions, joint ventures
and other significant transactions.

     Throughout the second and third quarters of 1999, senior management of
Cornerstone met on several occasions to determine whether or not Cornerstone
should undertake a comprehensive review of the strategic alternatives available
to the company. These discussions were included as part of Cornerstone's regular
strategic planning sessions. These discussions involved a review of the general
status of the industry, the industry's financial performance and trends in the
capital markets, as well as Cornerstone's financial performance and outlook, the
integration of the William Wilson & Associates merger completed in December
1998, Cornerstone's development pipeline and its asset disposition program. In
addition to an evaluation of Cornerstone's current strategy, this discussion
included an assessment of the potential for a strategic combination with another
office REIT.

     At the regularly scheduled Cornerstone board of directors meeting held on
September 28, 1999, John S. Moody, the president and chief executive officer of
Cornerstone, reviewed with the board the current strategic direction of the
company. In his review, Mr. Moody noted the challenges that faced

                                       30
<PAGE>   43

Cornerstone as a publicly traded REIT in the current market environment,
particularly in expanding its development capabilities outside of Northern
California, identifying significant acquisition candidates and accessing public
equity markets that were not receptive to REITs raising capital because of the
relative underperformance of REIT stocks in 1998 and 1999. At the September 28,
1999 Cornerstone board meeting, Lazard Freres & Co. LLC presented a financial
analysis of various strategic alternatives, including a more detailed analysis
of a hypothetical business combination of a specific potential merger partner
that had been previously identified to Lazard by Cornerstone's management team
as a logical candidate for a business combination. The board decided only to
explore the possibility of a merger transaction with this particular party. The
Cornerstone board authorized the engagement of Lazard to act as financial
advisor to Cornerstone and authorized management and Lazard to contact such
potential strategic partner to determine its interest in a possible business
combination.

     In October and November of 1999, representatives of Cornerstone and Lazard
met on several occasions with representatives of this potential merger partner
and provided financial and operating data regarding Cornerstone to assist the
other party in assessing a possible merger.

     In early December 1999, Mr. Moody telephoned Timothy H. Callahan, the
president and chief executive officer of Equity Office, to congratulate Mr.
Callahan on Equity Office's completion of the Lend Lease transaction. During the
conversation, Messrs. Callahan and Moody discussed the general state of the real
estate industry and public market valuations of real estate investment trusts.
Mr. Moody and Mr. Callahan also agreed during the call that public market
valuations of real estate investment trusts at the time made business
combinations very difficult. No specific acquisition proposal was discussed
between Messrs. Moody and Callahan during such conversation. This conversation
was one of several similar conversations Messrs. Moody and Callahan had over the
last several years about the real estate industry in general and the prospects
for consolidation among office real estate investment trusts in particular.
Other executives of Equity Office and Cornerstone also speak with each other
from time to time, as well as with executives of other real estate companies,
regarding the industry in general.

     On December 9, 1999, the Cornerstone board met to consider a preliminary
proposal from the party identified at the September 28, 1999 board meeting.
Lazard made a presentation regarding the financial aspects of the proposal. The
Cornerstone board discussed the proposal, asked questions of Lazard and
management and concluded that the proposal did not provide adequate value to the
stockholders of Cornerstone. Based on the advice of management, the board also
concluded that further discussions were not likely to result in a more
attractive proposal. The Cornerstone board also discussed the possibility of
initiating discussions with Equity Office, but determined that public market
valuations of real estate investment trusts at the time made pursuing a business
combination very difficult. Accordingly, the board terminated the engagement of
Lazard and directed management to cease any further discussions of a potential
business combination with the potential strategic partner and not to initiate
discussions with any other party, including Equity Office.

     During early January, Mr. Moody and Mr. Callahan again exchanged telephone
calls during which they agreed that the public markets had improved
significantly for real estate investment trusts over the past month. Mr.
Callahan further expressed an interest in meeting with Mr. Moody regarding a
possible business combination between Equity Office and Cornerstone. Mr. Moody
suggested to Mr. Callahan that he should come to New York and meet with him and
with William Wilson III, Cornerstone's chairman of the board. On January 10,
2000, Messrs. Callahan, Wilson and Moody met in New York and discussed the
benefits of a possible acquisition of Cornerstone by Equity Office. No
negotiations took place during this meeting. However, both sides agreed to
pursue additional discussions. On January 13, 2000, Equity Office and
Cornerstone executed a mutual confidentiality agreement and agreed to exchange
non-public information. On January 18, 2000, Mr. Callahan contacted J.P. Morgan,
Equity Office's financial advisor, and requested that J.P. Morgan commence its
research and analysis of Cornerstone.

     On January 19, 2000, Messrs. Wilson, Moody and Callahan and Samuel Zell,
Equity Office's chairman of the board, met in New York. At this meeting, Messrs.
Zell and Callahan expressed Equity Office's interest in acquiring Cornerstone in
a cash and stock merger, with Cornerstone common shares

                                       31
<PAGE>   44

valued at $17.50 per share, consisting of $6.56 in cash and $10.94 in Equity
Office common shares, subject to completion of due diligence. No negotiations
took place during this meeting, and Mr. Moody indicated that he would have to
ask the Cornerstone board for guidance as to whether to engage in further
discussions.

     On January 20, 2000, the Cornerstone board met at a regularly scheduled
meeting. Mr. Moody reported to the Cornerstone board Equity Office's offer to
acquire Cornerstone. At this meeting, the Cornerstone board did not authorize
management to enter into formal discussions with Equity Office, but decided to
engage Lazard to assist in an evaluation of the merits of a possible acquisition
of Cornerstone by Equity Office. Under a letter agreement dated January 28, 2000
between Cornerstone and Lazard, Lazard agreed to act as financial advisor to
Cornerstone in connection with the REIT merger. Over the next ten days,
representatives of Lazard met with representatives of Equity Office and J. P.
Morgan to exchange financial and operating data relating to Cornerstone and
Equity Office and to receive more information about the terms and structure of a
possible transaction.

     On January 31, 2000, the Cornerstone board met again to consider the Equity
Office proposal. Lazard reviewed the terms of the proposed transaction and
provided a financial analysis of the REIT transaction and other strategic
alternatives. At the meeting, the Cornerstone board discussed: (a) the financial
terms of the proposed transaction with Equity Office; (b) the potential benefits
of such a business combination; (c) the advantages and disadvantages of the
transaction compared with Cornerstone's other strategic alternatives; (d) the
potential conditions to the completion of the transaction, including approvals
of Cornerstone stockholders and limited partners of Cornerstone Partnership; and
(e) the tax consequences of the proposed transaction. At the conclusion of the
meeting, the Cornerstone board authorized management and Lazard to commence
formal negotiations with Equity Office with a principal objective of achieving a
higher price.

     At the regularly scheduled Equity Office board of trustees meeting held on
February 1, 2000, Mr. Callahan updated the board on the discussions with Messrs.
Wilson and Moody and Lazard regarding a possible acquisition of Cornerstone by
Equity Office. At this meeting, various members of the board expressed their
support for such a transaction if it could be accomplished along the lines
described at the meeting.

     During the week of January 31 through February 5, senior management of
Equity Office and Cornerstone, together with their respective financial
advisors, engaged in negotiations regarding the financial terms of the proposed
transaction. On February 5, Lazard asked Equity Office to submit its best and
final proposal for a merger transaction no later than the following morning. On
February 5, Equity Office submitted a revised merger proposal, which valued
Cornerstone common stock at $18.00 per share, consisting of $7.06 in cash and
$10.94 in Equity Office common shares, with the exchange ratio to be fixed based
upon the 10-day average closing share prices of Cornerstone and Equity Office
ending at the close of trading on Friday, February 4.

     The Cornerstone board met by telephone on the morning of Sunday, February 6
to consider the revised Equity Office proposal. Prior to that meeting, senior
management of Cornerstone and representatives of Lazard discussed by telephone
the terms of the proposal with representatives of PGGM, Cornerstone's largest
stockholder. After considering the proposal, PGGM indicated to management of
Cornerstone and Lazard that it was prepared to approve the revised proposal,
subject to satisfactory negotiation of the definitive agreements. During the
Cornerstone board meeting, Lazard reviewed the negotiations of the past week and
reviewed the financial terms of the revised proposal. At the conclusion of the
meeting, the Cornerstone board authorized management to negotiate a definitive
merger agreement and related documentation with Equity Office.

     From February 7, 2000 through February 10, 2000, management of Equity
Office and Cornerstone, and their respective legal and financial advisors, met
to negotiate the terms of the merger agreement, the mergers and the ancillary
documents, including the cash/share election mechanics, a stock option agreement
with the holders of the outstanding shares of Cornerstone preferred stock (see
"The Merger

                                       32
<PAGE>   45

Agreement -- Preferred Stock Option Agreement" on page 71) and the voting
agreements. Each of the parties also completed its due diligence review of the
other party.

     On the evening of February 10, 2000, the Equity Office board held a special
meeting at which members of management and representatives of J.P. Morgan and
Equity Office's outside counsel, Hogan & Hartson L.L.P., were present in person
or by conference telephone call. The special meeting was held in order for the
Equity Office board to consider and formally act upon the proposed acquisition
of Cornerstone. At this meeting, Equity Office's senior management reviewed with
the board financial and business terms of the proposed transaction, including
the need for Equity Office to finance the cash portion of the proposed REIT
merger consideration, and the results of Equity Office's due diligence review.
J.P. Morgan then presented its financial analysis of the proposed REIT merger,
and delivered to the Equity Office board its oral opinion that the REIT merger
consideration to be paid by Equity Office in the transaction was fair, from a
financial point of view, to Equity Office. Equity Office's legal counsel then
made a presentation to the Equity Office board in which it explained the
material terms of the proposed merger agreement and related agreements,
including closing conditions, termination rights and provisions regarding
break-up fees and termination expenses, and briefed the board on open items.

     Following these presentations, the Equity Office trustees asked numerous
questions of management and its legal counsel and financial advisors and
discussed at length the issues raised by the presentations. At the conclusion of
these discussions, the Equity Office board approved the REIT merger, the
partnership merger and the merger agreement on substantially the terms discussed
at the meeting, and authorized management to complete negotiations of, and
execute, the merger agreement, subject to final approval of the transaction
terms by the executive committee of the board and receipt of J.P. Morgan's
written fairness opinion.

     On the evening of February 10, 2000, the Cornerstone board met to review
and discuss the terms of the proposed merger agreement and related agreements.
Representatives of Lazard and Cornerstone's outside counsel, King & Spalding,
and senior management reviewed with the Cornerstone board the results of the
company's financial, business and legal due diligence examinations and the terms
of the merger agreement, the voting agreements, the stock option agreement and
the severance and non-competition arrangements with management of Cornerstone.
Lazard presented a financial analysis of the REIT merger and indicated that,
upon completion of definitive documentation relating to the REIT merger and the
partnership merger, it would deliver its opinion that the consideration to be
received in the REIT merger was fair, from a financial point of view, to the
holders of Cornerstone common stock. Counsel for Cornerstone made a presentation
to the Cornerstone board in which it explained the material terms of the
proposed merger agreement and related agreements, including closing conditions,
termination rights and provisions regarding break-up fees and termination
expenses, and highlighted the few issues that were as yet unresolved in the
merger agreement. The Cornerstone board directed management to continue
negotiations through the evening on the definitive merger agreement.

     Throughout the night of February 10, 2000, representatives of Equity Office
and Cornerstone and their respective legal counsel negotiated the remaining
unresolved terms of the merger agreement.

     On the morning of February 11, 2000, members of the executive committee of
the Equity Office board of trustees approved the final terms of the merger
agreement and the ancillary agreements and J.P. Morgan delivered its written
fairness opinion.

     On the morning of February 11, 2000, the Cornerstone board reconvened to
review and discuss the terms of the definitive merger agreement and related
agreements. Cornerstone's counsel reviewed the resolution of the issues that had
been unresolved as of the previous evening's meeting, and reviewed again the
terms of the definitive merger agreement, the voting agreements, the option
agreement with Deutsche Bank and the severance arrangements with management.
After discussion of the foregoing, the Cornerstone board determined that the
mergers were fair to and in the best interests of Cornerstone and the holders of
shares of Cornerstone stock and Cornerstone Partnership unitholders, that the
merger agreement and the transactions contemplated thereby were advisable and
that the board should recommend that the stockholders of Cornerstone and
Cornerstone Partnership unitholders approve the
                                       33
<PAGE>   46

merger agreement, the partnership merger and the REIT merger, as applicable, and
approved and adopted the merger agreement, the mergers, the voting agreements,
the option agreement and related matters. The Cornerstone board also determined
that the mergers and the merger agreement were advisable and in the best
interests of Cornerstone Partnership and the limited partners of Cornerstone
Partnership.

     Immediately after the Cornerstone board meeting on the morning of February
11, the parties executed the merger agreement, the option agreement, their
respective voting agreements and issued a joint press release announcing the
transaction.

EQUITY OFFICE'S REASONS FOR THE MERGERS

     As the general partner of EOP Partnership, Equity Office believes that the
mergers are in the best interests of Equity Office, EOP Partnership and their
respective securityholders. The Equity Office board of trustees has approved the
REIT merger, the merger agreement, and on behalf of Equity Office, in its
capacity as general partner of EOP Partnership, the partnership merger. No vote
of the limited partners of EOP Partnership is required under the partnership
agreement of EOP Partnership for the approval of the partnership merger. The
partnership agreement of EOP Partnership requires the approval of the REIT
merger by the consent of the limited partners holding at least a majority of the
outstanding EOP Partnership units, including EOP Partnership units held by
Equity Office. As of                , 2000, Equity Office owned approximately
88.2% of the outstanding EOP Partnership units. Accordingly, it intends to take
action by written consent, as permitted under the partnership agreement of EOP
Partnership to approve the REIT merger on or about                , 2000.

     In its deliberations with respect to the mergers and the merger agreement,
the Equity Office board consulted with Equity Office's management and the
financial and legal advisors to Equity Office. The factors considered by the
Equity Office board include those described below. While all of these factors
were considered by the Equity Office board, the board did not make
determinations with respect to each factor. Rather, the board made its judgment
with respect to the mergers and the merger agreement based on the total mix of
information available to it, and the judgments of individual trustees may have
been influenced to a greater or lesser degree by their individual views with
respect to different factors.

     POSITIVE FACTORS CONSIDERED BY THE EQUITY OFFICE BOARD

     In making its determination with respect to the mergers and the merger
agreement, the Equity Office board considered the following material positive
factors:

     - Cornerstone Partnership's class A office portfolio will enhance EOP
       Partnership's existing presence in such top U.S. markets as Boston, San
       Francisco, Washington, D.C., Seattle and Atlanta, all of which are
       continuing to experience significant job growth and many of which have
       significant impediments to new office supply;

     - the mergers present EOP Partnership with the opportunity to acquire a
       significant portfolio of well-located, high-quality office properties.
       Cornerstone Partnership currently owns or has interests in approximately
       82 class A office properties, which comprise nearly 18 million rentable
       square feet;

     - the mergers, by increasing the number of office properties operated by
       EOP Partnership by approximately 24% based on square footage, will
       solidify Equity Office's position as the largest publicly traded owner
       and operator of office properties in the United States. After the REIT
       merger, Equity Office will have an equity market capitalization of
       approximately $8.9 billion, assuming a share price of $25.68125, which
       equaled Equity Office's average closing share price for the ten business
       days from January 24, 2000 through February 4, 2000, and a total market
       capitalization of approximately $18.7 billion;

     - the mergers should generate efficiencies through anticipated cost savings
       and reductions in expenses;

     - the mergers should allow EOP Partnership to better meet the needs of its
       tenants by offering a fuller range of increased space options;

                                       34
<PAGE>   47

     - the Equity Office board believes that EOP Partnership should be able to
       manage Cornerstone Partnership's office properties efficiently following
       the mergers because of the significant geographic overlap of EOP
       Partnership's and Cornerstone Partnership's office portfolios;
       approximately two-thirds of Cornerstone Partnership's assets are in EOP
       Partnership's top eight core markets;

     - Cornerstone Partnership will provide EOP Partnership with an existing
       development pipeline in the San Francisco Bay area, which has significant
       supply constraints;

     - the amount of cash payable in the REIT merger and the exchange ratios
       applicable to both the REIT merger and the partnership merger are fixed
       and not subject to adjustment; and

     - the opinion, analyses and presentations of J.P. Morgan described under
       "Opinion of Equity Office's Financial Advisor" below, including the
       opinion of J.P. Morgan to the effect that, as of the date of such
       opinion, and based upon and subject to the matters stated therein, the
       consideration to be paid by Equity Office in the REIT merger is fair,
       from a financial point of view, to Equity Office.

     NEGATIVE FACTORS CONSIDERED BY THE EQUITY OFFICE BOARD

     The Equity Office board of trustees also considered the following
potentially negative factors in its deliberations concerning the mergers and the
merger agreement:

     - the need for EOP Partnership to obtain financing in order to distribute
       to Equity Office the cash that will be payable as part of the REIT merger
       consideration and the resulting increase in the level of borrowings of
       EOP Partnership and exposure to interest rate risk;

     - the risk that the anticipated benefits of the mergers to Equity Office,
       EOP Partnership, and their respective securityholders may not be realized
       as a result of possible changes in the real estate market in general, the
       inability to achieve the anticipated cost savings and reduction in
       expenses and other potential difficulties in integrating the companies
       and their respective operations;

     - the significant cost involved in connection with consummating the mergers
       and the substantial management time and effort required to effect the
       mergers and integrate the businesses of Equity Office and Cornerstone and
       of EOP Partnership and Cornerstone Partnership; and

     - the risk that the mergers might not be completed based upon the failure
       to satisfy covenants or closing conditions.

     In view of the wide variety of factors considered, the Equity Office board
did not quantify or otherwise attempt to assign relative weights to the specific
factors that it considered in making its determination. In the view of the
Equity Office board, however, the potentially negative factors considered by it
were not sufficient, either individually or collectively, to outweigh the
positive factors considered in its deliberations relating to the mergers and the
merger agreement.

OPINION OF EQUITY OFFICE'S FINANCIAL ADVISOR

     At the meeting of the board of trustees of Equity Office on February 10,
2000, J.P. Morgan rendered its oral opinion to the board of trustees of Equity
Office that, as of such date, the consideration to be paid by Equity Office in
the proposed REIT merger of Cornerstone into Equity Office was fair from a
financial point of view to Equity Office. J.P. Morgan confirmed its February 10,
2000 oral opinion by delivering its written opinion to the board of trustees of
Equity Office, dated February 11, 2000, that, as of such date, the consideration
to be paid by Equity Office in the proposed REIT merger was fair from a
financial point of view to Equity Office. No opinion was rendered by J.P. Morgan
with respect to the partnership merger. J.P. Morgan has not been requested to,
and will not, unless requested by Equity Office, update its opinion before the
closing of the REIT merger. No limitations were imposed by Equity Office's board
of trustees upon J.P. Morgan with respect to the investigations made or
procedures followed by it in rendering its opinion.

                                       35
<PAGE>   48

     The full text of the written opinion of J.P. Morgan dated February 11,
2000, which sets forth the assumptions made, matters considered and limits on
the review undertaken, is attached as Annex B to this consent
solicitation/information statement/prospectus and is incorporated herein by
reference. J.P. Morgan's written opinion, addressed to the board of trustees of
Equity Office, is directed only to the consideration to be paid in connection
with the REIT merger and does not constitute a recommendation to any shareholder
of Equity Office as to how such shareholder should vote at the Equity Office
special meeting being held to approve the REIT merger. The summary of the
opinion of J.P. Morgan set forth in this consent solicitation/information
statement/prospectus and in the joint proxy statement/prospectus delivered
simultaneously herewith is qualified in its entirety by reference to the full
text of such opinion.

     In arriving at its opinion, J.P. Morgan, among other things:

     - reviewed the merger agreement;

     - reviewed the audited financial statements for the twelve months ended
       December 31, 1998 and the unaudited financial statements for the nine
       months ended September 30, 1999 of Equity Office and Cornerstone;

     - reviewed current and historical market prices of Equity Office common
       shares and Cornerstone common stock;

     - reviewed publicly available information concerning the business of
       Cornerstone and of other companies engaged in businesses comparable to
       those of Cornerstone, and the reported market prices for other companies'
       securities deemed comparable;

     - reviewed publicly available terms of transactions involving companies
       comparable to Cornerstone and the consideration received for such
       companies;

     - reviewed the terms of other business combinations deemed relevant by J.P.
       Morgan;

     - reviewed internal financial analyses and estimates of budgeted 2000
       through 2004 funds from operations and net operating income prepared by
       Equity Office and Cornerstone and their respective management teams;

     - reviewed agreements with respect to outstanding indebtedness or
       obligations of Equity Office and Cornerstone;

     - held discussions with members of the management of Equity Office and
       Cornerstone with respect to various aspects of the REIT merger, and the
       past and current business operations of Equity Office and Cornerstone,
       the financial condition and future prospects and operations of Equity
       Office and Cornerstone and the effects of the REIT merger on the
       financial condition and future prospects of Equity Office and
       Cornerstone, and other matters believed necessary or appropriate to J.P.
       Morgan's inquiry; and

     - reviewed such other financial studies and analyses and considered such
       other information as J.P. Morgan deemed appropriate for the purposes of
       its opinion.

     J.P. Morgan relied upon and assumed, without independent verification, the
accuracy and completeness of all information that was publicly available or that
was furnished to it by Equity Office and Cornerstone or otherwise reviewed by
J.P. Morgan, and J.P. Morgan has not assumed any responsibility or liability
therefor. J.P. Morgan has not conducted any valuation or appraisal of any assets
or liabilities, nor have any valuations or appraisals been provided to J.P.
Morgan. In relying on financial analyses and forecasts provided to it, J.P.
Morgan has assumed that they have been reasonably prepared based on assumptions
reflecting the best currently available estimates and judgments by management as
to the expected future results of operations and financial condition of Equity
Office and Cornerstone to which such analyses or forecasts relate. J.P. Morgan
has also assumed that the REIT merger will have the tax consequences described
in discussions with representatives of Equity Office.

                                       36
<PAGE>   49

     No representation or warranty was made by any party with respect to the
internal financial analysis and estimates referred to above. Financial
projections are subject to contingencies beyond management's control and
realization of the projections depends on numerous factors, including among
other things, the cost of integrating the companies, the completion of pending
developments, the actual cost in relation to such projects and decisions by
management to modify business plans to address changing needs and a changing
operating environment. All material events and circumstances cannot be predicted
and unanticipated events and circumstances are likely to occur. Accordingly,
there may be differences between the projected results of operations and the
actual results of operations of the respective companies, and such differences
could be material. In the event that the financial projections prove to be
materially different, the conclusions reached in the opinion of J.P. Morgan
could be materially affected.

     J.P. Morgan's opinions are based on economic, market and other conditions
as in effect on, and the information made available to J.P. Morgan as of, the
date of such opinion. Subsequent developments may affect the written opinion
dated February 11, 2000. J.P. Morgan expressed no opinion as to the price at
which the Equity Office common shares or Cornerstone common stock will trade at
any future time.

     In accordance with customary investment banking practice, J.P. Morgan
employed generally accepted valuation methods in reaching its opinion. The
following is a summary of the material financial analyses utilized by J.P.
Morgan in connection with providing its opinion.

     Pro Forma Merger Analysis. J.P. Morgan analyzed the effect of the REIT
merger on, among other things, the estimated First Call funds from operations
per fully diluted Equity Office common share, including EOP Partnership units,
for the years ended December 31, 2000 and 2001. In doing so, J.P. Morgan
combined the projected operating results for Equity Office and Cornerstone and
assumed specified savings in general and administrative expenses as well as
additional costs related to the transaction as per estimates provided by the
management of Equity Office. J.P. Morgan observed a total projected post-REIT
merger incremental accretion of $0.01 and $0.04 to Equity Office's First Call
2000 and 2001 funds from operations estimates of $2.80 and $3.03 per share,
respectively. The analysis assumed a transaction closing date of June 30, 2000.
In calculating the purchase price for Cornerstone common stock and Cornerstone
Partnership units, a $25.68125 share price for Equity Office common shares was
assumed.

     J.P. Morgan also analyzed the effect of the REIT merger on Equity Office's
2000 pro forma equity market capitalization, total market capitalization,
leverage ratios and distribution payout ratio. In this regard, J.P. Morgan noted
that:

     - the pro forma equity market capitalization for Equity Office would be
       approximately $8.9 billion, assuming a share price of $25.68125, which
       equaled Equity Office's average closing share price for the ten business
       days from January 24, 2000 through February 4, 2000, and assuming
       347,044,557 Equity Office common shares and EOP Partnership units
       outstanding after completion of the merger, and a total post-REIT merger
       pro forma market capitalization of approximately $18.7 billion; these
       figures do not include the 250,770 shares of Cornerstone common stock
       already owned by Equity Office before the REIT merger;

     - Equity Office's debt to total market capitalization ratio would increase,
       upon completion of the REIT merger, from 43.8% before the merger to 48.9%
       after the assumption of Cornerstone's outstanding debt plus the
       incremental debt incurred for the cash portion of the transaction
       consideration and for the payment of transaction costs;

     - the ratio of debt plus preferred shares to total market capitalization
       also would increase from 48.2% to 52.2%, assuming the retirement of all
       outstanding Cornerstone preferred stock; and

     - Equity Office's intent is to retain its current distribution of $1.68 per
       share for the combined company.

     Net Asset Value Analysis. Using Equity Office's projections of
Cornerstone's performance results for the twelve-month period beginning July 1,
2000 and projected asset and liability balances as of June 30,

                                       37
<PAGE>   50

2000, J.P. Morgan calculated the net asset value per share for Cornerstone. In
so doing, J.P. Morgan applied a range of capitalization rates from 8.25% to
8.75% to Equity Office's projections of Cornerstone's stabilized July 1, 2000 to
June 30, 2001 net operating income for the properties, assuming no additional
net operating income from future acquisitions or developments. The resulting
gross real estate value was added to the gross value of Cornerstone's other
assets, including developments in progress, cash and marketable securities, and
fee income (valued at a 5.0x multiple of earnings before interest, taxes,
depreciation and amortization), less Cornerstone's outstanding debt, to arrive
at an equity net asset value. The equity net asset value per share was then
calculated by dividing the equity net asset value by the number of shares of
Cornerstone common stock and Cornerstone Partnership units outstanding on a
fully diluted basis. This analysis indicated a net asset value range of between
$18.59 and $20.35 per share. J.P. Morgan also noted that this range was
generally consistent with equity analysts' published net asset value per share
estimates for Cornerstone of $17.00 to $20.81, based on asset balances as of
September 30, 1999.

     Discounted Cash Flow Analysis. J.P. Morgan performed a discounted cash flow
analysis, that is, an analysis of the present value, calculated as of June 30,
2000, of the projected levered cash flows for the period from 2000 to 2004, of
Cornerstone based upon projections provided by Equity Office, using discount
rates reflecting an equity cost of capital ranging from 13.5% to 14.5% and
terminal value multiples applied to 2005 funds from operations ranging from 9.5x
to 10.5x. J.P. Morgan, for the purposes of this valuation, derived 2005 funds
from operations by growing 2004 funds from operations at a rate equal to the
compound annual growth rate of projected funds from operations from 2000-2004.
Based upon Equity Office's projections of Cornerstone cash flows for the years
2000 through 2004, the range of present values per share of Cornerstone common
stock was $18.27 to $20.35. J.P. Morgan noted that the implied price for
Cornerstone common stock was below the indicated discounted cash flow range.

     Selected Transaction Analysis. Using publicly available information, J.P.
Morgan examined selected transactions with respect to purchase price per share
to calculate both implied transaction premia and implied transaction funds from
operations multiples. Specifically, J.P. Morgan reviewed all publicly traded
REIT acquisitions since January 1, 1997 with total transaction values of at
least $500 million as follows:

<TABLE>
<CAPTION>
                  ACQUIROR                                        TARGET
                  --------                                        ------
<S>                                            <C>
Olympus Real Estate Fund II L.P.               Walden Residential Properties, Inc.
Berkshire Realty Holdings, L.P.                Berkshire Realty Company, Inc.
Duke Realty Investments, Inc.                  Weeks Corporation
The Irvine Company                             Irvine Apartment Communities, Inc.
ProLogis Trust                                 Meridian Industrial Trust, Inc.
Equity Residential Properties Trust            Merry Land & Investment Company, Inc.
Security Capital Pacific Trust                 Security Capital Atlantic Incorporated
Equity Office Properties Trust                 Beacon Properties Corporation
Equity Residential Properties Trust            Evans Withycombe Residential, Inc.
Equity Residential Properties Trust            Wellsford Residential Property Trust
</TABLE>

     J.P. Morgan observed a range of implied transaction premia over the target
companies' share price one week before the announcement date of 5.4% to 29.8%
with a median of 20.4%, resulting in a range of equity values for Cornerstone's
common stock of between $15.68 and $19.31 per share. In addition, J.P. Morgan
observed a range of implied transaction First Call funds from operations
multiples for the target companies from 9.4x to 14.8x with a median of 12.4x.
This range was then applied to Cornerstone's First Call 2000 funds from
operations per share of $1.69, resulting in a range of equity values for
Cornerstone's common stock of between $15.92 and $24.94 per share. J.P. Morgan
noted that the implied price for Cornerstone common stock was within the range
based on both transaction premia and transaction multiples.

     Public Trading Multiples Analysis. Using publicly available information,
J.P. Morgan compared selected financial and stock market data of Cornerstone
with similar data for selected publicly traded

                                       38
<PAGE>   51

companies which J.P. Morgan judged to be analogous to that of Cornerstone's.
These companies generally were those with sufficiently large total market
capitalization and specialization in the office REIT sector. The companies
selected by J.P. Morgan were:

     - Boston Properties Inc.;

     - CarrAmerica Realty Corporation;

     - Equity Office Properties Trust;

     - Mack-Cali Realty Corporation;

     - Speiker Properties; and

     - Vornado Realty Trust.

     For each comparable company, publicly available financial performance data
through the nine months ended September 30, 1999 was measured. J.P. Morgan
calculated the multiples of current stock price, as of February 4, 2000, to
analysts' estimates for 2000 First Call funds from operations for each of the
comparable companies to determine the 2000 funds from operations trading
multiples. J.P. Morgan's calculations resulted in a range of 2000 funds from
operations multiples from 7.0x to 10.7x with a median of 9.1x. These multiples
were then applied to Cornerstone's First Call 2000 funds from operations per
share estimate as of February 4, 2000 of $1.69, yielding a range of implied
trading values for Cornerstone's common stock of approximately $11.83 to $18.08
per share. J.P. Morgan noted that the implied price for Cornerstone common stock
was within the indicated trading multiples range. J.P. Morgan also observed that
the comparable companies had a range of debt to total market capitalization of
38.8% to 56.7%.

     Share Trading History Analysis. Based on publicly available information,
J.P. Morgan reviewed the history of trading prices for Cornerstone common stock
for the 52-week and 104-week periods ending February 4, 2000. The 52-week
trading range was $13.06 to $16.94 per share and the 104-week trading range was
$13.06 to $18.38 per share. J.P. Morgan noted that the implied price for
Cornerstone common stock was at a premium to the 52-week high, but at a discount
to the 104-week high.

     The summary set forth above is not a complete description of the analyses
or data presented by J.P. Morgan. The preparation of a fairness opinion is a
complex process and is not necessarily susceptible to partial analysis or
summary description. J.P. Morgan believes that the summary set forth above and
their analyses must be considered as a whole and that selecting portions,
without considering all of its analyses, could create an incomplete view of the
processes underlying its analyses and opinion. J.P. Morgan based its analyses on
assumptions that it deemed reasonable, including assumptions concerning general
business and economic conditions and industry-specific factors. The other
principal assumptions upon which J.P. Morgan based its analyses are set forth
above under the description of each such analysis. J.P. Morgan's analyses are
not necessarily indicative of actual values or actual future results that might
be achieved, which values may be higher or lower than those indicated. Moreover,
J.P. Morgan's analyses are not and do not purport to be appraisals or otherwise
reflective of the prices at which businesses actually could be bought or sold.

     As a part of its investment banking business, J.P. Morgan and its
affiliates are continually engaged in the valuation of businesses and their
securities in connection with mergers and acquisitions, investments for passive
and control purposes, negotiated underwritings, secondary distributions of
listed and unlisted securities, private placements, and valuations for estate,
corporate and other purposes. J.P. Morgan was selected to deliver an opinion to
Equity Office's board of trustees with respect to the REIT merger on the basis
of such experience and its familiarity with Equity Office.

     For the delivery of its opinion and related advisory work, J.P. Morgan will
receive a total fee of $7.0 million from Equity Office. $1.0 million was due and
payable upon announcement of the REIT merger, with the remaining $6.0 million
payable upon the successful close of the REIT merger. In addition, Equity Office
reimbursed J.P. Morgan for its reasonable expenses incurred in connection with
its

                                       39
<PAGE>   52

services, including the fees and disbursements of counsel, and agreed to
indemnify J.P. Morgan against certain liabilities, including liabilities arising
under the federal securities laws.

     J.P. Morgan and its affiliates, including Morgan Guaranty Trust Company of
New York, maintain banking and other business relationships with Equity Office
and its affiliates pursuant to which J.P. Morgan has received an aggregate of
approximately $3.1 million in fees over the past two years. In July 1998, J.P.
Morgan provided a fairness opinion to the William Wilson & Associates investors
relating to the merger of WWA with Cornerstone. J.P. Morgan received a fee of
$500,000 from the WWA investors for the delivery of its opinion in the
transaction. In the ordinary course of their businesses, J.P. Morgan and its
affiliates may actively trade the debt and equity securities of Equity Office or
Cornerstone for their own accounts or for the accounts of customers and,
accordingly, they may at any time hold long or short positions in such
securities.

CORNERSTONE'S REASONS FOR THE MERGERS

     The Cornerstone board of directors approved the REIT merger and approved
and adopted the merger agreement at a meeting held on February 11, 2000. On
behalf of Cornerstone, in its capacity as general partner of Cornerstone
Partnership, the Cornerstone board also approved the partnership merger. The
Cornerstone board believes that the terms of the mergers, the merger agreement
and the other transactions contemplated thereby are advisable and in the best
interests of Cornerstone, Cornerstone Partnership and their respective
securityholders.

     In considering the recommendation of the Cornerstone board with respect to
the mergers and the merger agreement, Cornerstone Partnership unitholders should
be aware that, following completion of the mergers, three current members of the
Cornerstone board will become trustees of Equity Office. Also, Messrs. Wilson,
Moody and Dimock will receive severance benefits as a result of the REIT merger.
See "-- Interests of Cornerstone's Directors and Officers in the
Mergers -- Retention Agreements" on page 48. Therefore, these Cornerstone
directors have interests in the mergers that are different from, or in addition
to, the interests of the Cornerstone stockholders and the Cornerstone
Partnership unitholders generally.

     In its deliberations with respect to the mergers and the merger agreement,
the Cornerstone board consulted with Cornerstone's management and the financial
and legal advisors to Cornerstone. The factors considered by the Cornerstone
board include those described below. While all of these factors were considered
by the Cornerstone board, the board did not make determinations with respect to
each factor. Rather, the board made its judgment with respect to the mergers and
the merger agreement based on the total mix of information available to it, and
the judgments of individual directors may have been influenced to a greater or
lesser degree by their individual views with respect to different factors.

     POSITIVE FACTORS CONSIDERED BY THE CORNERSTONE BOARD

     In making its determination with respect to the mergers and the merger
agreement, the Cornerstone board considered the following material positive
factors:

     - in the partnership merger, each Cornerstone Partnership Class A common
       unit will be exchanged for 0.7009 of an EOP Partnership Class A unit.
       Consequently, based on the closing price of Equity Office common shares
       of $25.6875 on February 10, 2000, the last full trading day before the
       mergers were publicly announced, each Cornerstone Partnership class A
       common unit will be exchanged in the partnership merger for an EOP
       Partnership class A unit having a redemption value of approximately
       $18.00, representing a 21% premium over the closing price of $14.875 for
       Cornerstone common stock, into which a Cornerstone Partnership class A
       common unit is convertible on a one-for-one basis, on February 10, 2000.
       In addition, Cornerstone Partnership unitholders will be able to redeem
       their units for Cornerstone common stock and participate in the REIT
       merger as Cornerstone common stockholders;

     - in the REIT merger, each share of Cornerstone common stock will be
       converted, at the election of the stockholder, into either $18.00 per
       share in cash, without interest, or 0.7009 of a common share

                                       40
<PAGE>   53

       of Equity Office, subject to proration if either the cash election or the
       share election is oversubscribed. Consequently, based on the closing
       price of Equity Office common shares of $25.6875 on February 10, 2000,
       the last full trading day before the mergers were publicly announced,
       each Cornerstone common share will be exchanged in the REIT merger for
       either $18.00 in cash or for 0.7009 of an Equity Office common share
       having a value of approximately $18.00, representing a 21% premium over
       the closing price of $14.875 for Cornerstone common stock on February 10,
       2000;

     - the combined companies will have an increased presence in major markets,
       which should enhance revenue opportunities by providing additional space
       options to existing Cornerstone Partnership and EOP Partnership tenants;

     - the increased diversity of markets should reduce the combined companies'
       dependence on any single market or region, thereby reducing the risk that
       a regional economic downturn could affect a large number of their
       properties;

     - after the partnership merger, EOP Partnership, by virtue of its larger
       size and investment grade credit rating, should have improved access to
       capital markets, which should make additional debt or other financing
       available upon more attractive terms;

     - the unit-for-unit nature of the partnership merger will provide
       Cornerstone Partnership unitholders with the opportunity to share in any
       future appreciation of EOP Partnership while deferring at least a portion
       of the taxable gain that would be recognized in a cash transaction;

     - Cornerstone Partnership and EOP Partnership have complimentary product
       focus and operating strategies, which should result in a successful
       integration of the two companies;

     - the mergers may generate additional efficiencies through anticipated cost
       savings and reductions in expenses;

     - the opinion, analysis and presentations of Lazard regarding the REIT
       merger described under "Opinion of Cornerstone's Financial Advisor"
       below, including the opinion of Lazard to the effect that, as of the date
       of such opinion, and based upon and subject to the matters stated
       therein, the consideration to be received in the REIT merger was fair,
       from a financial point of view, to the holders of common stock of
       Cornerstone; and

     - other strategic alternatives available to Cornerstone and Cornerstone
       Partnership, including the prospects of positioning Cornerstone and
       Cornerstone Partnership for the future and enhancing long-term
       stockholder and unitholder value by remaining an independent company or
       by effecting a strategic business combination with another company, were
       not as attractive as the proposed mergers with Equity Office and EOP
       Partnership.

     NEGATIVE FACTORS CONSIDERED BY THE CORNERSTONE BOARD

     The Cornerstone board of directors also considered the following
potentially negative factors in its deliberations concerning the mergers and the
merger agreement:

     - the exchange ratio is fixed and not subject to adjustment. As a result, a
       decrease in the trading price of Equity Office common shares before the
       effective time of the mergers will reduce the value of the aggregate
       consideration that will be received by the Cornerstone common
       stockholders and Cornerstone Partnership unitholders;

     - the risk that the anticipated benefits of the mergers to securityholders
       may not be realized as a result of possible changes in the real estate
       market in general, or as a result of the inability to achieve the
       anticipated reduction in expenses and other potential difficulties in
       integrating the companies and their respective operations;

     - the effect of the public announcement of the mergers on Cornerstone's and
       Cornerstone Partnership's ability to retain employees and on the trading
       price of Cornerstone's common stock;
                                       41
<PAGE>   54

     - the significant cost involved in connection with consummating the
       mergers, the substantial management time and effort required to
       effectuate the mergers and integrate the businesses of the companies and
       the related disruption to Cornerstone Partnership's operations; and

     - the risk that the mergers might not be completed based upon the failure
       to satisfy certain covenants or closing conditions.

     The Cornerstone board also considered certain matters described above under
"Risk Factors," including the potential benefits to certain directors and
officers discussed in "Risk Factors -- The directors and officers of Cornerstone
may have interests in the completion of the mergers that are different from the
interests of Cornerstone' Partnership's unitholders and Cornerstone's
stockholders."

IN VIEW OF THE WIDE VARIETY OF FACTORS CONSIDERED, THE CORNERSTONE BOARD DID NOT
QUANTIFY OR OTHERWISE ATTEMPT TO ASSIGN RELATIVE WEIGHTS TO THE SPECIFIC FACTORS
THAT IT CONSIDERED IN MAKING ITS DETERMINATION. IN THE VIEW OF THE CORNERSTONE
BOARD, HOWEVER, THE POTENTIALLY NEGATIVE FACTORS CONSIDERED BY IT WERE NOT
SUFFICIENT, EITHER INDIVIDUALLY OR COLLECTIVELY, TO OUTWEIGH THE POSITIVE
FACTORS CONSIDERED IN ITS DELIBERATIONS RELATING TO THE MERGERS AND THE MERGER
AGREEMENT.

OPINION OF CORNERSTONE'S FINANCIAL ADVISOR

     THE OPINION OF LAZARD ADDRESSES ONLY THE FAIRNESS OF THE REIT MERGER AND
DOES NOT ADDRESS ANY ASPECT OF THE PARTNERSHIP MERGER. LAZARD'S OPINION IS
ADDRESSED TO THE CORNERSTONE BOARD OF DIRECTORS AND NOT TO CORNERSTONE
PARTNERSHIP, NOR ITS GENERAL PARTNER, NOR ITS LIMITED PARTNERS NOR ITS
UNITHOLDERS. ACCORDINGLY, NO PARTNER OR UNITHOLDER OF CORNERSTONE PARTNERSHIP
SHOULD OR IS ENTITLED TO RELY ON LAZARD'S OPINION IN EVALUATING THE TERMS AND
CONDITIONS OF THE PARTNERSHIP MERGER. THE BOARD OF DIRECTORS OF CORNERSTONE
BELIEVES, HOWEVER, THAT THE LAZARD OPINION IS RELEVANT TO THE UNITHOLDERS OF
CORNERSTONE PARTNERSHIP.

     At the meeting of the Cornerstone board of directors on February 10, 2000,
Lazard rendered its oral opinion to the Cornerstone board of directors that, as
of such date, the consideration to be received in the REIT merger was fair, from
a financial point of view, to the holders of common stock of Cornerstone. Lazard
confirmed its February 10, 2000 oral opinion by delivering to the Cornerstone
board of directors its written opinion dated February 11, 2000, that, as of such
date, the consideration to be received in the REIT merger was fair, from a
financial point of view, to the holders of common stock of Cornerstone. Lazard's
analysis of the REIT merger assumed that prior to the REIT merger each holder of
units in Cornerstone Partnership will have elected to exercise its redemption
right and receive shares of common stock in Cornerstone in exchange therefor in
the manner provided in the merger agreement. Lazard has not been requested to
and will not update its opinion before the closing of the REIT merger. No
limitations were imposed by the Cornerstone board of directors upon Lazard with
respect to the investigations made or the procedures followed by it in rendering
its opinion.

     THE FULL TEXT OF THE WRITTEN OPINION OF LAZARD DATED FEBRUARY 11, 2000,
WHICH SETS FORTH THE ASSUMPTIONS MADE, MATTERS CONSIDERED AND LIMITS ON THE
REVIEW UNDERTAKEN, IS ATTACHED AS ANNEX C TO THIS CONSENT
SOLICITATION/INFORMATION STATEMENT/PROSPECTUS. THE WRITTEN OPINION OF LAZARD
SHOULD BE READ IN ITS ENTIRETY. LAZARD'S WRITTEN OPINION, ADDRESSED TO THE
CORNERSTONE BOARD OF DIRECTORS, IS DIRECTED ONLY TO THE FAIRNESS OF THE
CONSIDERATION TO BE RECEIVED IN THE REIT MERGER TO THE HOLDERS OF COMMON STOCK
OF CORNERSTONE AND DOES NOT CONSTITUTE A RECOMMENDATION TO ANY UNITHOLDER OF
CORNERSTONE PARTNERSHIP AS TO WHETHER SUCH UNITHOLDER SHOULD CONSENT TO THE
MERGERS. THE SUMMARY OF THE OPINION OF LAZARD SET FORTH IN THIS CONSENT
SOLICITATION/INFORMATION STATEMENT/PROSPECTUS IS QUALIFIED IN ITS ENTIRETY BY
REFERENCE TO THE FULL TEXT OF SUCH OPINION.

                                       42
<PAGE>   55

     In arriving at its opinion on the REIT merger, Lazard, among other things:

     - reviewed the merger agreement as to only the REIT merger;

     - analyzed historical business and financial information relating to
       Cornerstone and Equity Office, including the audited financial statements
       for the twelve months ended December 31, 1998 and the unaudited financial
       statements for the nine months ended September 30, 1999 of Cornerstone
       and Equity Office;

     - reviewed the historical stock prices and trading volumes of Cornerstone's
       common stock and Equity Office's common shares;

     - reviewed financial forecasts and other data provided to Lazard by
       Cornerstone and Equity Office relating to their businesses;

     - reviewed public information with respect to certain other companies in
       lines of businesses Lazard believed to be comparable to the business of
       Cornerstone;

     - reviewed the financial terms of certain recent business combinations
       involving companies in lines of business Lazard believed to be comparable
       to those of Cornerstone;

     - held discussions with members of the senior management of Cornerstone and
       Equity Office with respect to the respective businesses of Cornerstone
       and Equity Office; and

     - conducted such other financial studies, analyses and investigations as
       Lazard deemed appropriate for the purposes of its opinion.

     Lazard relied upon and assumed, without independent verification, the
accuracy and completeness of all information that was furnished to it by Equity
Office and Cornerstone or otherwise reviewed by Lazard, and Lazard has not
assumed any responsibility or liability for the independent verification of such
information or any independent valuation or appraisal of any of the assets or
liabilities of Cornerstone or Equity Office, or concerning the solvency or fair
value of Cornerstone, Cornerstone Partnership, Equity Office, EOP Partnership or
any other entity. In relying on financial analyses and forecasts provided to it,
Lazard has assumed that they have been reasonably prepared based on assumptions
reflecting the best currently available estimates and judgments by management as
to the expected future results of operations and financial condition of Equity
Office and Cornerstone to which such analyses or forecasts relate. Lazard
assumed no responsibility for and expressed no view as to such forecasts or the
assumptions on which they were based. Lazard has also assumed that the REIT
merger will have the tax consequences described in discussions with
representatives of Cornerstone.

     No representation or warranty was made by any party with respect to the
financial analyses and estimates referred to above. Financial projections are
subject to contingencies beyond management's control and realization of the
projections depends on numerous factors, including among other things, the cost
of integrating the companies, the completion of pending developments, the actual
cost in relation to such projects and decisions by management to modify business
plans to address changing needs and a changing operating environment. All
material events and circumstances cannot be predicted and unanticipated events
and circumstances are likely to occur. Accordingly, there may be differences
between the projected results of operations and the actual results of operations
of the respective companies, and such differences could be material. In the
event that the financial projections prove to be materially different, the
conclusions reached in the opinion of Lazard could be materially affected.

     In rendering its opinion regarding the REIT merger, Lazard assumed that the
REIT merger would be consummated on the terms described in the merger agreement,
without any waiver of any material terms or conditions by Cornerstone or
Cornerstone Partnership, and that obtaining the necessary regulatory approvals
for the REIT merger would not have a material adverse effect on Cornerstone or
Cornerstone Partnership. Lazard's opinions are based on economic, market and
other conditions as in effect on, and the information made available to Lazard
as of, the date of such opinion. Subsequent developments may affect

                                       43
<PAGE>   56

the written opinion dated February 11, 2000. Lazard expressed no opinion as to
the price at which the Equity Office common shares or Cornerstone common stock
will trade at any future time.

     In arriving at its opinion and making its presentation on the REIT merger
to the Cornerstone board of directors at the February 10, 2000 meeting of the
board, Lazard considered and discussed certain financial analyses and other
factors. In connection with its presentation on the REIT merger on February 10,
2000, Lazard provided the Cornerstone board of directors with a summary of
results obtained by using several different valuation methods as well as other
materials concerning the common stock and business of Cornerstone.

     The following paragraphs summarize Lazard's presentation on the REIT
merger.

     Public Market Valuation Analysis. Lazard reviewed and compared the
financial and market performance of the following group of eight public United
States REITs:

     - Spieker Properties, Inc.;

     - Boston Properties, Inc.;

     - Equity Office Properties Trust;

     - Vornado Realty Trust;

     - Duke-Weeks Realty Corporation;

     - CarrAmerica Realty Corporation;

     - Mack-Cali Realty Corporation; and

     - Crescent Real Estate Equities Company.

     Lazard examined certain publicly available financial data of the selected
companies and published consensus funds from operations estimates for the
selected companies to derive multiples of share price to projected funds from
operations per share for the fiscal years ending December 31, 1999 and December
31, 2000. The REIT merger price implied funds from operations multiples of
11.39x and 10.65x for 1999 and 2000, respectively, which are higher than the
median funds from operations multiples of the selected companies of 9.49x and
8.56x for 1999 and 2000, respectively.

                                       44
<PAGE>   57

     Comparable Transaction Analysis. Lazard reviewed the consideration proposed
to be paid in 18 other comparable acquisitions of publicly traded REIT
companies. Specifically, Lazard reviewed the following transactions:

<TABLE>
<CAPTION>
                 ACQUIROR                                     TARGET                    DATE
                 --------                                     ------                    ----
<S>                                         <C>                                         <C>
Equity Office Properties Trust              Beacon Properties Corporation               1997
Excel Realty Trust, Inc.                    New Plan Realty Trust                       1998
Equity Residential Properties Trust         Evans Withycombe Residential, Inc.          1997
The Irvine Company                          Irvine Apartment Communities, Inc.          1998
Kimco Realty Corporation                    The Price REIT, Inc.                        1998
Equity Residential Properties Trust         Wellsford Residential Property Trust        1997
Bay Apartment Communities, Inc.             Avalon Properties, Inc.                     1998
Security Capital Pacific Trust              Security Capital Atlantic Incorporated      1998
Post Properties, Inc.                       Columbus Realty Trust                       1997
ProLogis Trust                              Meridian Industrial Trust, Inc.             1998
Equity Residential Properties Trust         Merry Land & Investment Company, Inc.       1998
Apartment Investment & Management Company   Ambassador Apartments, Inc.                 1997
Camden Property Trust                       Oasis Residential, Inc.                     1997
Duke Realty Investments, Inc.               Weeks Corporation                           1999
Aptco LLC                                   Berkshire Realty Company, Inc.              1999
Public Storage, Inc.                        Storage Trust Realty                        1998
Reckson Associates                          Tower Realty Trust, Inc.                    1998
Prime Retail, Inc.                          Horizon Group, Inc.                         1997
</TABLE>

     For each such transaction, Lazard calculated the multiples of merger price
to projected funds from operations per share. The funds from operations multiple
implied by the REIT merger price was 10.54x, which was below 11.63x, the median
implied funds from operations multiple for the selected transactions. However,
Lazard did not view such result as significant due to the substantial decrease
in the stock prices and funds from operations multiples of office and other
REITs since August 1998. Comparing only those mergers announced since August 1,
1998, the REIT merger price is above the median implied funds from operations
multiple of 9.95x for such mergers.

     Discounted Cash Flow Analysis. Lazard aggregated (x) the present value of
the projected cash flow of Cornerstone after interest expense and capital
expenditures over the three-year period from 2000 to 2002 with (y) the present
value of the range of terminal values described below. The range of terminal
values was calculated by applying multiples of 8.0x to 10.0x to Cornerstone's
projected funds from operations for the fiscal year 2003. This range of terminal
values represented Cornerstone's value beyond 2002. As part of the discounted
cash flow analysis, Lazard used discount rates ranging from 13% to 15%. Based on
the discounted cash flow analysis, Lazard calculated a range of the equity value
per share of Cornerstone of $14.37 to $18.01.

     Net Asset Value Analysis. Lazard also calculated the net asset value of
Equity Office and Cornerstone on a combined basis based on the net asset value
for each company separately based on an 8.25% capitalization rate on 2000 net
operating income and other information provided by each company's management.
Certain adjustments were made to arrive at the combined company's net asset
value. The proposed transaction provides a net increase to net asset value per
share of $0.06 to Cornerstone stockholders.

     Accretion/Dilution Analysis. Lazard's merger model assumed that the REIT
merger closes on July 1, 2000 and is based on modified versions of the internal
budgets of Equity Office and Cornerstone that exclude some investments not yet
completed, including selected development projects and acquisitions. General and
administrative expense reductions for Equity Office and Cornerstone on a
combined basis were assumed to save $20 million annually. Purchase accounting
was assumed for accounting purposes and

                                       45
<PAGE>   58

debt was marked-to-market and lease revenues were re-straight lined accordingly.
Based on the above assumptions and such budgets, Cornerstone's funds from
operations per share for 2001 was calculated to be $2.11 if the REIT merger is
completed versus $1.79 if the REIT merger is not completed.

     Premiums Paid Analysis. Lazard reviewed the consideration proposed to be
paid in 18 other comparable acquisitions of publicly traded REIT companies.
Specifically, Lazard reviewed the following transactions:

<TABLE>
<CAPTION>
                 ACQUIROR                                     TARGET                    DATE
                 --------                                     ------                    ----
<S>                                         <C>                                         <C>
Equity Office Properties Trust              Beacon Properties Corporation               1997
Aptco LLC                                   Berkshire Realty Company, Inc.              1999
The Irvine Company                          Irvine Apartment Communities, Inc.          1998
Security Capital Pacific Trust              Security Capital Atlantic Incorporated      1998
Equity Residential Properties Trust         Evans Withycombe Residential, Inc.          1997
Kimco Realty Corporation                    The Price REIT, Inc.                        1998
Excel Realty Trust, Inc.                    New Plan Realty Trust                       1998
ProLogis Trust                              Meridian Industrial Trust, Inc.             1998
Equity Residential Properties Trust         Merry Land & Investment Company, Inc.       1998
Duke Realty Investments, Inc.               Weeks Corporation                           1999
Camden Property Trust                       Oasis Residential, Inc.                     1997
Reckson Associates                          Tower Realty Trust, Inc.                    1998
Equity Residential Properties Trust         Wellsford Residential Property Trust        1997
Apartment Investment & Management Company   Ambassador Apartments, Inc.                 1997
Post Properties, Inc.                       Columbus Realty Trust                       1997
Prime Retail, Inc.                          Horizon Group, Inc.                         1997
Bay Apartment Communities, Inc.             Avalon Properties, Inc.                     1998
Public Storage, Inc.                        Storage Trust Realty                        1998
</TABLE>

     For each such transaction, Lazard calculated the percentage premium
represented by the excess of (x) the acquisition price per share payable in such
transaction over (y) the closing stock price of the target company on the
trading day immediately prior to the announcement of such transaction. The
implied premium represented by the REIT merger price of 21.52% was significantly
higher than the median of the implied premiums for the selected transactions of
11.71%.

     Stock Trading History. Lazard examined the history of trading prices for
Cornerstone common stock. Cornerstone went public in April 1997 at a price of
$14.50 per share. Since its initial public offering, Cornerstone common stock
has traded as high as $20.00 per share and as low as $13.00 per share. Over the
52 weeks ended February 9, 2000, Cornerstone common stock traded as high as
$17.00 and as low as $13.00. The average closing price of Cornerstone common
stock during the 30-day period ended February 9, 2000, was $14.97. The REIT
merger price represents a premium of 20.3% over such 30-day average closing
price and is 5.9% above Cornerstone's 52-week high.

     The summary set forth above does not purport to be a complete description
of the analyses performed by Lazard. The preparation of a fairness opinion is a
complex process and is not necessarily susceptible to partial analysis or
summary description. In arriving at its opinion and in preparing its
presentation, Lazard performed a variety of financial analyses, the material
portions of which are summarized above. In addition, Lazard believes that its
analyses must be considered as a whole and that selecting portions of such
analyses and the factors considered by it, without considering all of such
analyses and factors, could create an incomplete view of the process underlying
its analyses set forth in the opinion and its presentation to the Cornerstone
board of directors. With regard to the public market valuation, premiums paid
and comparable transaction analysis summarized above, Lazard selected comparable
public companies on the basis of various factors, including the size of the
public company or portfolio of properties and similarity of the line of
business; however, no public company or portfolio of properties utilized as a

                                       46
<PAGE>   59

comparison is identical to Cornerstone. Accordingly, an analysis of the
foregoing is not mathematical; rather, it involves complex considerations and
judgments concerning differences in financial and operating characteristics of
the comparable companies or portfolios and other factors that could affect the
acquisition or public trading value of the comparable companies or portfolios to
which Cornerstone or its properties are being compared.

     In performing its analyses, Lazard made numerous assumptions with respect
to industry performance, general business and economic conditions and other
matters, many of which are beyond Cornerstone's control. Any estimates contained
in such analyses are not necessarily indicative of actual past or future results
or values, which may be significantly more or less than such estimates.
Estimates of values of companies or parts of companies do not purport to be
appraisals or necessarily to reflect the price at which such companies or parts
may actually be sold, and such estimates are inherently subject to uncertainty.

     Lazard is an internationally recognized investment banking firm that
regularly engages in the valuation of businesses and their securities in
connection with mergers and acquisitions. The Cornerstone board of directors
selected Lazard to act as its financial advisor in regards to only the REIT
merger on the basis of Lazard's international reputation and experience in
connection with the office REIT industry, Cornerstone's prior relationship with
Lazard and Lazard's familiarity with Cornerstone.

     Under a letter agreement dated January 28, 2000 between Cornerstone and
Lazard, Lazard agreed to act as financial advisor to Cornerstone in connection
with the REIT merger. Pursuant to the engagement letter, Cornerstone is
obligated to pay Lazard a fee of $1 million upon the execution of the definitive
merger agreement and upon the closing of the REIT merger will be obligated to
pay Lazard a fee of $7 million. Cornerstone also agreed to reimburse Lazard for
its reasonable out-of-pocket expenses and to indemnify Lazard and certain
related persons against certain liabilities, including liabilities under the
federal securities laws, relating to, or arising out of, its engagement.

     Lazard and its affiliates maintain business relationships with Cornerstone,
Cornerstone Partnership and their affiliates pursuant to which Lazard has
received an aggregate of approximately $9 million in fees since February 1,
1998. Lazard has not received any fees over the past two years from Equity
Office, EOP Partnership or their affiliates. In the ordinary course of their
businesses, Lazard and its affiliates may actively trade the debt and equity
securities of Equity Office, EOP Partnership, Cornerstone or Cornerstone
Partnership for their own accounts or for the accounts of customers and,
accordingly, they may at any time hold long or short positions in such
securities.

     As noted under the caption "Cornerstone's Reasons for the Mergers" the
fairness opinion of Lazard on the REIT merger was only one of the many factors
considered by the Cornerstone board of directors in determining to approve and
adopt the merger agreement.

INTERESTS OF CORNERSTONE'S DIRECTORS AND OFFICERS IN THE MERGERS

     In considering the recommendation of the Cornerstone board with respect to
the REIT merger and the partnership merger, Cornerstone stockholders and
Cornerstone Partnership unitholders should be aware that, as described below,
certain Cornerstone directors and officers and PGGM have interests in the
mergers that differ from, or are in addition to, the interests of unitholders
and stockholders generally.

     Trustees of Equity Office After the REIT Merger. Following the mergers, the
current trustees of Equity Office will remain as trustees of the combined
entity. In addition, three current directors of Cornerstone will become trustees
of the combined entity. See "-- Equity Office Board of Trustees and Executive
Officers after the Mergers" on page 49.

     Equity-Based Awards. Under Cornerstone's incentive stock plans, an
aggregate of 89,113 unvested shares of restricted common stock previously
awarded to executives who are parties to the retention agreements described
below will vest in full upon completion of the mergers and will be converted
into cash or common shares of Equity Office according to the terms of the merger
agreement. In addition, unvested options to purchase an aggregate of 3,177,476
shares of Cornerstone common stock previously awarded to such executives will
vest in full upon completion of the mergers, and each option may be
                                       47
<PAGE>   60

surrendered within two business days following the REIT merger by the holder of
the option to Equity Office for cash equal to the difference between $18.00 per
share and the exercise price of the option or exchanged for options to purchase
common shares of Equity Office according to the terms of the merger agreement.
Cornerstone and Equity Office have agreed that the REIT merger will constitute a
change in control for purposes of all applicable Cornerstone benefit and
compensation plans, including the Cornerstone 1998 Long Term Incentive Plan and
all stock option and restricted stock agreements provided under the terms of
such plans.

     Mr. Moody has agreed with Cornerstone to waive the acceleration of his
unvested restricted stock and unvested stock options.

     Moody Agreement. Cornerstone has entered into a contract with Mr. Moody
whereby amounts are accrued under an unfunded arrangement to pay Mr. Moody a
supplemental pension. Under the contract, his supplemental pension account was
established with a credit of $250,000 as of July 1, 1995, and Cornerstone is
obligated to credit the account in the amount of $60,000 each subsequent July 1
during the continuance of Mr. Moody's employment.

     The account is also credited with any deemed income, gains or losses which
would be attributable to a corresponding investment of an equal cash amount in
such investment as Cornerstone, taking into account Mr. Moody's views, shall
deem the account to be invested. Payment of Mr. Moody's supplemental pension
account is to be made in a lump sum as of the date Mr. Moody terminates his
employment. However, if his employment is terminated for cause, Mr. Moody will
forfeit the account and no payment will be made. The contract also provides
that, outside of a change in control context, if Mr. Moody's employment
terminates for a reason other than cause, an additional credit of $60,000 (or
less, if Mr. Moody resigns without good reason) will be made to the account.
Following a change in control, in the event Mr. Moody's employment is terminated
by Cornerstone other than for cause, or if he resigns for good reason,
Cornerstone is obligated to credit his supplemental pension account with an
amount equal to $60,000 times the number of years, including fractional portions
of a year, remaining between his age on the date his employment ceases and age
60.

     Retention Agreements. Cornerstone has entered into retention agreements
with some of its officers to address the terms and conditions of their
employment in the event of a change in control. A "change in control" generally
is said to occur when: (a) any person becomes the owner of 25% or more of
Cornerstone's voting securities; (b) directors who constitute the Cornerstone
board at the beginning of any two-year period, and any new directors whose
election or nomination for election was approved by a vote of at least three
quarters of the directors then in office who either were directors at the
beginning of such period or whose election or nomination for election was
previously so approved, cease to constitute a majority; (c) a merger,
consolidation or reorganization in which Cornerstone's voting securities do not
continue to represent at least 50% of the surviving entity; or (d) a
reorganization, liquidation, or sale of all or substantially all of
Cornerstone's assets.

     In the event of termination of employment by Cornerstone without cause, or
by the employee for good reason, within two years following a change in control,
Cornerstone will make a lump sum payment of: (a) the pro rata portion of the
annual bonus for the year termination occurred, calculated on the basis of the
target bonus and on the assumption that all performance goals have been or will
be achieved; and (b) three times annual compensation in the case of Messrs.
Wilson, Moody, Van Boven and Dimock and two times annual compensation in the
case of all other officers. Annual compensation generally is defined as the
salary in effect immediately before termination or change in control, plus the
highest of the target annual bonus for the termination year or the average of
the three annual bonuses paid immediately prior to the termination or the change
in control.

     An officer may be terminated for "cause" if he or she is convicted of a
felony, reveals confidential information about Cornerstone or refuses to
substantially perform his duties. An officer can terminate for "good reason" if
Cornerstone reduces his salary or bonus target, reduces the value of employee
benefits materially, relocates his office more then 25 miles from the present
location, detrimentally alters his title or

                                       48
<PAGE>   61

position, fails to get a successor to agree to assume the obligations under the
retention agreement or materially breaches any provision of the agreement.

     In addition, the officer and his eligible dependents will continue to be
eligible to participate during the benefit continuation period in the medical,
dental, health, life and other welfare benefit plans and arrangements applicable
to him immediately before his or her termination of employment, on the same
terms and conditions in effect immediately before such termination. "Benefit
continuation period" means the period beginning on the day of termination and
ending on the earlier to occur of: (a) the third anniversary of the date of
termination in the case of Messrs. Wilson, Moody, Van Boven and Dimock and the
second anniversary of the date of termination in the case of all other officers;
and (b) the date that the officer is eligible and elects coverage under the
plans of a subsequent employer which provide substantially equivalent or greater
benefits to the officer and his dependents.

     If the payments to an officer under the retention agreement constitute
"parachute payments," as defined in section 280G of the Internal Revenue Code,
and the officer would receive more value after taxes if the payments to be made
to the officer were capped at three times the "base amount" less $1.00, then the
payments will be reduced to that amount.

     Equity Office has agreed to assume and to perform Cornerstone's obligations
under the retention agreements in the same manner and to the same extent that
Cornerstone would be required to perform such obligations if the REIT merger had
not taken place. The parties have agreed that the REIT merger will be a "change
in control" for purposes of the retention agreements.

     Mr. Moody has agreed to waive any rights to payment of the lump sum payment
and to the continuation of benefits under his retention agreement in
consideration of Cornerstone's payment to Mr. Moody upon completion of the REIT
merger, in recognition of his past service to Cornerstone, of $7,342,614 or, if
the REIT merger is completed on or after July 1, 2000, $6,772,262. Messrs. Van
Boven and Dimock have each agreed to waive the payment of $1,000,000, and Mr.
Moran has agreed to waive the payment of $500,000, of the lump sum payment
otherwise payable to each of them in the event of the termination of their
employment other than for cause after the REIT merger.

     Noncompetition Agreements. Each of Messrs. Moody, Van Boven, Dimock and
Moran have agreed to enter into noncompetition agreements with Equity Office
that will restrict their ability to engage in business activities that are
competitive with those of Equity Office after the mergers. In order to induce
Messrs. Moody, Van Boven, Dimock and Moran to enter into such agreements, Equity
Office will pay $5,000,000 to Mr. Moody, $1,000,000 to each of Messrs. Van Boven
and Dimock and $500,000 to Mr. Moran upon the completion of the mergers.

     Escrowed Units. In connection with the acquisition of William Wilson &
Associates in December 1998, an aggregate of 387,137 partnership units issued by
the Cornerstone Partnership that would have been distributable to the general
partners or managers of the four Wilson-sponsored opportunity funds acquired by
Cornerstone in the transaction were placed in escrow pursuant to an agreement
with certain investors in the opportunity funds. These units would have been
distributed to these general partners and managers under the governing
instruments of the opportunity funds if the units were valued at $17.25 per
unit, the agreed-upon value of the Cornerstone shares and units issued in the
Wilson transaction. The units were placed in escrow pending a determination of
their value during the one-year period beginning on the date the units were
released from the lockup provisions applicable to the units issued in the Wilson
acquisition. Mr. Wilson and other executive officers of Cornerstone indirectly
beneficially own in the aggregate 319,369 of such escrowed units.

EQUITY OFFICE BOARD OF TRUSTEES AND EXECUTIVE OFFICERS AFTER THE MERGERS

     Following the mergers, the current trustees of Equity Office will remain as
trustees of the combined entity. In addition, three current directors of
Cornerstone, John S. Moody, Jan H.W.R. van der Vlist and William Wilson III,
will become trustees of the combined entity, with their terms expiring in 2002,
2003 and 2003, respectively. Under the terms of the merger agreement, Equity
Office is obligated to nominate

                                       49
<PAGE>   62

Mr. van der Vlist for reelection to the board of trustees in 2003 and 2006 if
PGGM and its affiliates continue to own at least 21,000,000 of the issued and
outstanding Equity Office common shares, as adjusted for stock splits or similar
actions, at all times up to the time the trustees are being elected in those
years. If Mr. van der Vlist fails to stand for reelection in 2003 or 2006 for
any reason, or in the event of his death or earlier resignation, and if PGGM
continues to own at least 21,000,000 of the issued and outstanding Equity Office
shares as described above, Equity Office is required to take all action
necessary to nominate a replacement designated by PGGM for election or
re-election as a trustee for an additional three-year term, subject to Equity
Office's approval if the replacement is not an officer, director or employee of
PGGM.

     Following the mergers, the current executive officers of Equity Office will
remain as executive officers of Equity Office. No current executive officers of
Cornerstone will become executive officers of Equity Office following the
mergers.

ASSUMPTION OF CORNERSTONE'S OBLIGATIONS UNDER REGISTRATION RIGHTS AGREEMENTS

     Under the merger agreement, Equity Office has agreed to assume
Cornerstone's obligations under existing registration rights agreements between
Cornerstone and certain holders of Cornerstone Partnership units.

     In addition, under the merger agreement, Equity Office has agreed to assume
Cornerstone's obligations under the amended and restated registration rights and
voting agreement, dated December 16, 1998, among Cornerstone, PGGM and Dutch
Institutional Holding Company, Inc., as amended by the voting agreement entered
into concurrently with the merger agreement among Equity Office, EOP
Partnership, WCP Services, Inc. and PGGM. Under this registration rights
agreement, PGGM will have the following rights relating to the registration of
Equity Office common shares:

     - Demand Registration: subject to specified limitations, PGGM will have the
       right to demand, on no more than eight occasions, that Equity Office
       register all or a portion of the Equity Office common shares issued to
       PGGM under the merger agreement, subject to a requirement that the market
       value of the shares requested to be registered as of the date of any
       demand must be equal to or greater than (a) $75 million or (b) the total
       aggregate amount of shares held by PGGM, if less than $75 million. Equity
       Office must use its commercially reasonable efforts to effect any such
       demand registration and will have the ability to defer the filing of a
       registration statement relating to a demand in specified circumstances;

     - Shelf Registration: within 20 days after the request of PGGM following
       the effective time of the REIT merger, Equity Office will use its
       commercially reasonable efforts to register all of the Equity Office
       common shares issued to PGGM in connection with the merger agreement on a
       registration statement which provides for the offering of such securities
       on a delayed or continuous basis. Before selling Equity Office common
       shares under such registration statement, PGGM must give written notice
       to Equity Office of its intent to sell Equity Office common shares.
       Equity Office will have the right in specified circumstances to defer
       such intended sales; and

     - "Piggyback" Registration: in the event that Equity Office exercises its
       rights to defer a requested registration, or suspend the effectiveness of
       the shelf registration or sales of Equity Office common shares by PGGM
       due to a contemplated public offering of Equity Office common shares,
       PGGM will have the right to include its shares in Equity Office's
       registration statement relating to such public offering. These
       "piggyback" registration rights will be subject to specified customary
       limitations as well as limitations contained in the other agreements
       between Equity Office and its shareholders.

     All registrations of PGGM shares described above will be at the expense of
Equity Office, except that PGGM will bear all underwriting discounts and
commissions and fees and expenses of its own counsel.

     In addition under the amended and restated registration rights and voting
agreement, PGGM has agreed to a "standstill" provision which provides that PGGM
will not take any of the following actions
                                       50
<PAGE>   63

until 90 days after the date on which no Equity Office trustee nominated by PGGM
in accordance with the PGGM voting agreement described below on page 71 remains
a trustee of Equity Office:

     - directly or indirectly purchase or otherwise acquire, or propose or offer
       to purchase or otherwise acquire, any of Equity Office's equity
       securities if, immediately after such purchase or acquisition, PGGM and
       its affiliates would own 12% or more of the Equity Office common shares.
       "Equity security" means any (a) Equity Office common shares, (b)
       securities of Equity Office that are convertible into or exchangeable for
       Equity Office common shares, and (c) options, rights, warrants and
       similar securities issued by Equity Office to acquire Equity Office
       common shares;

     - directly or indirectly propose to Equity Office or any person or entity a
       "business combination," which is defined to mean any one of the following
       transactions: (a) any merger or consolidation of Equity Office or any
       Equity Office subsidiary with any person or entity, other than Equity
       Office; (b) any sale, lease exchange, mortgage, pledge, transfer or other
       disposition by Equity Office, in one transaction or a series of
       transactions to or with any person or entity, of all or a substantial
       portion of the assets of Equity Office and its subsidiaries taken as a
       whole; (c) the adoption of any plan or proposal for the liquidation or
       dissolution of Equity Office proposed by or on behalf of PGGM or any
       affiliate of PGGM; or (d) any reclassification of securities (including
       any reverse share split), recapitalization of Equity Office, or any
       merger or consolidation of Equity Office with any of its subsidiaries, or
       any other transaction to which Equity Office is a party which has the
       effect, directly or indirectly, of increasing the proportionate share of
       PGGM or any affiliate of PGGM, whether or not with or into or otherwise
       involving PGGM or any affiliate of PGGM;

     - make, or in any way participate in, any "solicitation" of "proxies" to
       vote, as those terms are used in the rules promulgated by the SEC under
       section 14(a) of the Securities Exchange Act of 1934, or seek to advise,
       encourage or influence any person or entity with respect to the voting of
       any capital shares of Equity Office, initiate, propose or otherwise
       solicit shareholders of Equity Office for the approval of one or more
       shareholder proposals or induce or attempt to induce any other person or
       entity to initiate any shareholder proposal; or

     - deposit any equity securities of Equity Office into a voting trust or
       subject any equity securities to any arrangement or agreement with
       respect to the voting of such securities, or form, join or in any way
       participate in a "group," within the meaning of section 13(d)(3) of the
       Securities and Exchange Act of 1934, with respect to any equity
       securities, except as contemplated by the registration rights agreement.

     The standstill provision may be waived by Equity Office only upon the
approval of a majority of its board, excluding any trustee nominated by PGGM,
and is not applicable to actions approved by the majority of the Equity Office
board, excluding any trustee nominated by PGGM in circumstances in which any
trustee nominated by PGGM is an "interested director" under section 2-419 of the
Maryland General Corporation Law as applicable to REITs.

ACCOUNTING TREATMENT

     EOP Partnership will treat the partnership merger as a purchase for
financial accounting purposes. This means that EOP Partnership will record the
assets acquired and liabilities assumed at their estimated fair values at the
time the partnership merger is completed.

RESALES OF EOP PARTNERSHIP UNITS AND EQUITY OFFICE COMMON SHARES

     The EOP Partnership units to be issued to Cornerstone Partnership
unitholders in the partnership merger will be transferable subject to the
restrictions contained in the partnership agreement of EOP Partnership. The
Equity Office common shares to be issued to (a) Cornerstone common stockholders
in the REIT merger, including Cornerstone Partnership unitholders who elect to
redeem their Cornerstone Partnership units under the partnership agreement of
Cornerstone Partnership prior to the REIT merger where solely Cornerstone common
stock is used, other than the use of Cornerstone common stock in

                                       51
<PAGE>   64

connection with equity-based employee benefit plans or as necessary to maintain
REIT status and (b) the Cornerstone Partnership unitholders upon redemption of
their EOP Partnership units received in the partnership merger, in each case,
have been registered under the Securities Act, and will be transferable freely
and without restriction by those holders of Cornerstone common stock and
Cornerstone Partnership units who receive such shares following consummation of
the REIT merger or upon redemption of the EOP Partnership units issued pursuant
thereto and who are not deemed to be an "affiliate" of Equity Office or
Cornerstone within the meaning of rule 145 under the Securities Act or who will
become an "affiliate" of Equity Office within the meaning of rule 144 under the
Securities Act after the REIT merger. Equity Office common shares received by
persons who are deemed to be Cornerstone affiliates or who become Equity Office
affiliates may be resold by these persons only in transactions permitted by the
limited resale provisions of rule 145 or as otherwise permitted under the
Securities Act. Persons who may be deemed to be affiliates of Cornerstone
generally include individuals or entities that, directly or indirectly through
one or more intermediaries, control, are controlled by or are under common
control with Cornerstone and may include officers, directors and principal
stockholders of Cornerstone. All Cornerstone stockholders who may be deemed to
be affiliates of Cornerstone will be so advised before the completion of the
REIT merger.

     Under the merger agreement, Cornerstone will use its commercially
reasonable efforts to obtain an affiliate agreement from each affiliate of
Cornerstone before the completion of the REIT merger by which each Cornerstone
affiliate will agree not to sell, transfer, pledge or otherwise dispose of any
of the Equity Office common shares received in the REIT merger in violation of
the Securities Act or the rules and regulations promulgated under the Securities
Act. Generally, this will require that all sales be made in accordance with rule
145 under the Securities Act, which in turn requires that, for specified
periods, sales be made in compliance with the volume limitations, manner of sale
provisions and current information requirements of rule 144 under the Securities
Act.

     Equity Office has the right to place legends on the certificates evidencing
Equity Office common shares issued to Cornerstone affiliates in the REIT merger
summarizing the foregoing restrictions until a sale, transfer, pledge or other
disposition of the Equity Office common shares represented by these certificates
has been registered under the Securities Act or is made in compliance with rule
145 under the Securities Act.

     Persons who are not affiliates of Cornerstone may generally sell their
Equity Office common shares without restrictions and without delivering this
consent solicitation/information statement/prospectus.

NO APPRAISAL RIGHTS

     Cornerstone Partnership and EOP Partnership are organized under Delaware
law. Holders of Cornerstone Partnership units are not entitled to appraisal
rights as a result of the partnership merger under Delaware law, the partnership
agreement of Cornerstone Partnership or the merger agreement.

                              THE MERGER AGREEMENT

     The following is a summary of the material terms of the merger agreement
and is qualified in its entirety by reference to the merger agreement, which is
attached at the back of this consent solicitation/information
statement/prospectus as Annex A. You should read the merger agreement as it is
the legal document that governs the mergers.

CLOSING; EFFECTIVE TIME OF THE PARTNERSHIP MERGER AND THE REIT MERGER

     The completion of the partnership merger will occur no later than the third
business day after the satisfaction or waiver of the conditions set forth in the
merger agreement or at such other date or time as may be agreed by Equity Office
and Cornerstone. If the REIT merger is approved at the special meetings, Equity
Office and Cornerstone currently expect to complete the partnership merger and
the REIT merger on that same day.

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<PAGE>   65

     As soon as practicable after all conditions to the completion of the
mergers are satisfied, EOP Partnership will execute and file a certificate of
merger with the Secretary of State of the State of Delaware relating to the
partnership merger, and immediately after the completion of the partnership
merger, Equity Office and Cornerstone will execute and file articles of merger
with the State Department of Assessments and Taxation of Maryland and with the
Secretary of State of the State of Nevada relating to the REIT merger. The
effective time of the partnership merger will be the time specified in the
certificate of merger. The effective time of the REIT merger will be the time
specified in the articles of merger.

THE PARTNERSHIP MERGER

     The merger agreement contemplates the following two-step transaction:

     - the partnership merger, whereby Cornerstone Partnership will merge with
       and into EOP Partnership and Cornerstone Partnership will cease to exist;
       followed by

     - the REIT merger, whereby Cornerstone will merge with and into Equity
       Office and Cornerstone will cease to exist.

     In the partnership merger, holders of class A units of limited partnership
interest in Cornerstone Partnership, including Cornerstone, who have not elected
to redeem their units for shares of Cornerstone common stock will receive, for
each class A common unit issued and outstanding immediately before the
partnership merger, 0.7009 of a class A unit of limited partnership interest in
EOP Partnership, rounded to the nearest whole unit.

     REDEMPTION RIGHT UNDER THE PARTNERSHIP AGREEMENT OF CORNERSTONE PARTNERSHIP

     Instead of participating in the partnership merger, you may exercise any
unit redemption right that you currently have under the partnership agreement of
Cornerstone Partnership at any time before the partnership merger. Any exercise
by you of your unit redemption right under the partnership agreement of
Cornerstone Partnership will not be conditioned on completion of the mergers. By
exercising your unit redemption right under the partnership agreement of
Cornerstone Partnership, you would not receive units of EOP Partnership in the
partnership merger, but instead would receive shares of Cornerstone common stock
on a one-for-one basis for each Cornerstone Partnership unit redeemed and you
would participate in the REIT merger on the same basis as other common
stockholders of Cornerstone if you continued to own the Cornerstone common stock
at the time of the REIT merger. Generally, a Cornerstone Partnership unit is
redeemable commencing one year after the date it was first issued. Accordingly,
if you received your Cornerstone Partnership units less than one year ago, you
do not have a currently exercisable unit redemption right under the partnership
agreement of Cornerstone Partnership.

     CONDITIONAL UNIT REDEMPTION RIGHT UNDER THE MERGER AGREEMENT

     Under the merger agreement, you have the right to redeem all or a portion
of your Cornerstone Partnership units for Cornerstone common stock on a
one-for-one basis, whether or not you have a currently exercisable right to
redeem your units under the partnership agreement of Cornerstone Partnership.
The exercise by you of the unit redemption right under the merger agreement will
be effective only if the partnership merger is completed. Under the merger
agreement, you also may condition your redemption of units on the ability to
receive in the REIT merger only cash for some or all of the Cornerstone common
stock that you would receive upon redemption of your Cornerstone Partnership
units.

THE REIT MERGER

     In the REIT merger:

     - holders of Cornerstone common stock may elect to receive either $18.00
       per share in cash, without interest, or 0.7009 of an Equity Office common
       share, subject to proration if either the cash election or the share
       election is oversubscribed, as described below; and
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<PAGE>   66

     - holders of Cornerstone 7.0% cumulative convertible preferred stock will
       receive $18.00 per share in cash, without interest, together with accrued
       and unpaid dividends through the date of the closing of the REIT merger.

     Under the merger agreement, a total of 58,551,525 shares of Cornerstone
common stock will be converted in the REIT merger into the right to receive
$18.00 per share in cash, without interest, and the number of shares of
Cornerstone common stock issued and outstanding immediately before the REIT
merger in excess of 58,551,525 shares will be converted into the right to
receive Equity Office common shares based on the 0.7009 exchange ratio. Upon
conversion of the outstanding shares of Cornerstone common stock and preferred
stock into merger consideration, the Cornerstone common stock and preferred
stock will be cancelled and retired and will cease to exist.

     Because the aggregate cash portion of the REIT merger consideration to the
Cornerstone common stockholders is fixed at approximately $1.054 billion, or
$18.00 times 58,551,525 shares, and the number of Equity Office common shares
issuable in the merger is fixed at 0.7009 times the number of shares of
Cornerstone common stock issued and outstanding immediately before the closing
of the REIT merger in excess of 58,551,525 shares, the amount of cash and the
number of Equity Office common shares that each Cornerstone stockholder will
receive in the REIT merger may be subject to proration based on the elections
made by the Cornerstone common stockholders and redeeming Cornerstone
Partnership unitholders.

     For example:

     OVERSUBSCRIPTION OF CASH

     If cash elections are received in the REIT merger for more than 58,551,525
shares of Cornerstone common stock and you have elected to redeem some or all of
your Cornerstone Partnership units without condition, then you will receive in
the REIT merger:

     - 0.7009 of an Equity Office common share in exchange for each share of
       Cornerstone common stock for which you did not make a cash election; and

     - a combination of cash and Equity Office common shares, on a proportionate
       basis, for each share of Cornerstone common stock for which you made a
       cash election, so that the aggregate number of shares of Cornerstone
       common stock converted into cash in the REIT merger equals 58,551,525
       shares, with Equity Office common shares issued in exchange for the
       remainder of the shares of Cornerstone common stock converted in the REIT
       merger.

     If you condition the exercise of your unit redemption right under the
merger agreement on the ability to receive only cash for some or all of the
Cornerstone common stock that you would receive in the redemption, an
oversubscription of cash will cause the cash condition not to be satisfied and
you will receive EOP Partnership units in the partnership merger based on the
0.7009 exchange ratio for the units that were subject to the cash condition.
However, if there is an undersubscription of cash, taking into account cash
elections made by all Cornerstone common stockholders, but not including cash
elections made by Cornerstone Partnership unitholders who conditioned their unit
redemptions on the ability to receive cash in the REIT merger, you may
nevertheless have the opportunity to have your units redeemed for Cornerstone
common stock and receive cash in the REIT merger if the cash consideration
available after giving effect to cash elections made by the Cornerstone common
stockholders is sufficient to meet your specified cash condition and your
conditional cash redemption is chosen by lot from among other conditional cash
redemptions that were not initially satisfied. For any units redeemed by you
that were not subject to the cash election condition, you will receive cash or
Equity Office common shares, as elected by you, subject to the proration
provisions described above.

     OVERSUBSCRIPTION OF SHARES

     If share elections are received for more shares of Cornerstone common stock
than the difference between (a) the number of shares of Cornerstone common stock
issued and outstanding immediately

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<PAGE>   67

before the REIT merger, taking into account shares of Cornerstone common stock
issued to Cornerstone Partnership unitholders who exercise their unit redemption
rights, and (b) the 58,551,525 shares to be converted into cash in the REIT
merger, and you have elected to redeem some or all of your Cornerstone
Partnership units, then you will receive in the REIT merger:

     - $18.00 in cash, without interest, in exchange for each share of
       Cornerstone common stock for which you did not make a share election; and

     - a combination of cash and Equity Office common shares, on a proportionate
       basis, for each share of Cornerstone common stock for which you make a
       share election, so that the aggregate number of shares of Cornerstone
       common stock converted into cash in the REIT merger equals 58,551,525
       shares, with Equity Office common shares issued for the remainder of the
       shares of Cornerstone common stock converted in the REIT merger.

     If there is an oversubscription of Equity Office common shares, the cash
condition to any conditional redemption will be met because cash will be
available for each share of Cornerstone common stock for which cash was elected.

     UNDERSUBSCRIPTION OF CASH AND SHARES

     If cash elections are received for less than 58,551,525 shares of
Cornerstone common stock AND share elections are received for less than the
maximum number of shares of Cornerstone common stock to be converted into Equity
Office common shares in the REIT merger, and you have elected to redeem some or
all of your Cornerstone Partnership units, then you will receive in the REIT
merger:

     - $18.00 in cash, without interest, in exchange for each share of
       Cornerstone common stock for which you made a cash election;

     - 0.7009 of an Equity Office common share in exchange for each share of
       Cornerstone common stock for which you made a share election; and

     - a combination of cash and Equity Office common shares, on a proportionate
       basis, for each share of Cornerstone common stock for which you made
       neither a cash election nor a share election, so that the aggregate
       number of shares of Cornerstone common stock converted into $18.00 in
       cash, without interest, in the REIT merger equals 58,551,525 shares, with
       Equity Office common shares based on the 0.7009 exchange ratio issued for
       the remainder of the shares of Cornerstone common stock converted in the
       REIT merger.

     If there is an undersubscription of cash and an undersubscription of Equity
Office common shares, the cash condition to any conditional unit redemption will
be met because cash will be available for each share of Cornerstone common stock
for which cash was elected.

     Because the exchange ratio is fixed at 0.7009, the market value of any
Equity Office common shares that Cornerstone common stockholders will receive in
the REIT merger, including any Cornerstone Partnership unitholders who elect to
redeem their units prior to the partnership merger, may differ from $18.00 per
share and from the market value of the Equity Office common shares if the REIT
merger occurred today. On             , 2000, the closing price of Equity Office
common shares was $     per share, which, based on the 0.7009 exchange ratio,
would equal a market value equivalent per share of Cornerstone common stock of
$     had the REIT merger been completed on that date. You should obtain current
market prices for Equity Office common shares and shares of Cornerstone common
stock.

     A redemption notice and form of election accompany this document. If you
would like to redeem your Cornerstone Partnership units for Cornerstone common
stock and elect to receive cash or Equity Office common shares instead of
receiving EOP Partnership units in the partnership merger, please fill out the
notice of redemption/form of election and return it in the postage-paid envelope
provided at least two business days prior to the date of the Cornerstone
stockholders meeting. See "Cornerstone Partnership Consent Solicitation" on page
27.

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<PAGE>   68

TREATMENT OF CORNERSTONE STOCK OPTIONS

     Upon the completion of the mergers, each Cornerstone stock option
outstanding under Cornerstone's 1998 long-term incentive plan or any other
arrangement, whether or not then vested or exercisable, other than options
surrendered as provided below, will become fully exercisable and vested and each
such Cornerstone stock option will be automatically converted upon the
completion of the mergers into an option to purchase Equity Office common
shares. The substituted option will permit its holder to purchase a number of
Equity Office common shares equal to the number of shares of Cornerstone common
stock that could have been purchased, assuming full vesting, under the
corresponding Cornerstone stock option, multiplied by 0.7009. The exercise price
per Equity Office common share of the substituted option will be equal to the
per-share option exercise price specified in the Cornerstone stock option
divided by 0.7009. Each substituted option will otherwise be subject to the same
terms and conditions as the corresponding Cornerstone stock option.

     Holders of Cornerstone stock options also will have the option to surrender
to Equity Office any or all of their options, after the completion of the
mergers and before the end of the second business day immediately following the
completion of the mergers, in exchange for an amount in cash equal to:

     - the excess, if any, of $18.00 over the exercise price of such Cornerstone
       stock option; multiplied by

     - the number of shares of Cornerstone common stock subject to that
       Cornerstone stock option.

REPRESENTATIONS AND WARRANTIES OF EOP PARTNERSHIP AND CORNERSTONE PARTNERSHIP

     The merger agreement contains customary representations and warranties by
each of Cornerstone, Cornerstone Partnership, Equity Office and EOP Partnership
relating to, among other things:

     - due organization and good standing;

     - capitalization;

     - authorization to enter into the merger agreement and to consummate the
       REIT merger or the partnership merger, as applicable;

     - enforceability of the merger agreement;

     - no breach of organizational documents or material agreements as a result
       of the merger agreement or the consummation of the REIT merger or the
       partnership merger, as applicable;

     - required governmental and third-party consents;

     - compliance with SEC reporting requirements;

     - no undisclosed liabilities;

     - no changes since December 31, 1998 that would have a material adverse
       effect;

     - no material legal proceedings;

     - real property;

     - environmental matters;

     - tax matters;

     - finders' fees;

     - compliance with laws;

     - contracts and debt instruments;

     - receipt of opinion of financial advisor;

     - anti-takeover statutes;

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<PAGE>   69

     - compliance with the Investment Company Act of 1940; and

     - required stockholder and partner approvals.

     In addition, the merger agreement contains customary representations and
warranties by each of Cornerstone and Cornerstone Partnership relating to, among
other things:

     - related party transactions;

     - employee benefits and labor matters; and

     - payments to employees, officers and directors as a result of the mergers
       or a termination of service after the mergers.

CONDUCT OF BUSINESS OF EQUITY OFFICE AND EOP PARTNERSHIP PENDING THE MERGERS

     Pending the mergers, each of Equity Office and EOP Partnership has agreed
to, among other things:

     - preserve intact its business organizations and goodwill;

     - use commercially reasonable efforts to keep available the services of its
       officers and employees;

     - confer on a regular basis with Cornerstone to report material operational
       matters that would reasonably be expect to have a material adverse effect
       on the business properties, assets, financial condition or results of
       operations of Equity Office and its subsidiaries taken as a whole;

     - promptly notify Cornerstone of any material emergency or other material
       change in its condition, business, properties, assets, liabilities or
       prospects, or of any material governmental complaints, investigations or
       hearings;

     - promptly deliver to Cornerstone true and correct copies of any report,
       statement or schedule filed with the SEC;

     - maintain its books and records in accordance with GAAP consistently
       applied, and not to change any of its methods, principles or practices of
       accounting in any material manner, except as required by the SEC,
       applicable law or GAAP; and

     - duly and timely file all reports, tax returns and other documents
       required to be filed with federal, state, local and other authorities,
       subject to extensions permitted by law, provided such extensions do not
       adversely affect Equity Office's status as a qualified REIT under the
       Internal Revenue Code.

     In addition, pending the mergers, each of Equity Office and EOP Partnership
has agreed that, without Cornerstone's prior written consent or except as
otherwise expressly contemplated by the merger agreement, neither Equity Office
and EOP Partnership nor any of its subsidiaries will, among other things:

     - make or rescind any express or deemed election relating to taxes unless
       required by law or necessary to preserve Equity Office's status as a REIT
       or the status of any subsidiary of Equity Office as a partnership for
       federal income tax purposes or as a qualified REIT subsidiary as defined
       under the Internal Revenue Code, as the case may be;

     - amend their organizational documents, except in specified instances,
       including the proposed amendments to Equity Office's declaration of trust
       described in the joint proxy statement/ prospectus delivered to Equity
       Office shareholders and Cornerstone stockholders simultaneously with the
       delivery of this consent solicitation/information statement/prospectus;

     - authorize, declare, set aside or pay any dividend, other than regular
       quarterly dividends, or regular distributions pursuant to the partnership
       agreement of EOP Partnership, or redemptions of EOP Partnership units
       under the partnership agreement of EOP Partnership where solely Equity
       Office common shares are used, or redemptions of Equity Office common
       shares under its declaration of trust to maintain REIT status or
       repurchases of its common shares pursuant to its publicly announced share
       repurchase program;

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<PAGE>   70

     - enter into or agree to effect any merger, acquisition, consolidation,
       reorganization or other business combination with any third party in
       which Equity Office is not the surviving party to the transaction or
       enter into or agree to effect any merger, acquisition, exchange offer or
       other business combination with a third party in which Equity Office is
       the surviving party that would result in the issuance of equity
       securities representing in excess of 20% of the outstanding Equity Office
       common shares on the date any such business combination is entered into
       or agreed to unless, in either case, such business combination is
       approved by Cornerstone, which approval will not be unreasonably withheld
       or delayed, or the business combination agreement provides that the
       required vote of Equity Office shareholders for approval of such business
       combination is no less than the affirmative vote of holders of Equity
       Office common shares representing more than 50% of the sum of the number
       of Equity Office common shares outstanding at the time of such approval
       plus 50,000,000; and

     - authorize, recommend, propose or announce an intention to do any of the
       foregoing prohibited actions, or enter into any contract, agreement,
       commitment or arrangement to do any of the foregoing prohibited actions.

CONDUCT OF BUSINESS OF CORNERSTONE AND CORNERSTONE PARTNERSHIP PENDING THE
MERGERS

     Pending the mergers, each of Cornerstone and Cornerstone Partnership has
agreed to, among other things:

     - conduct its business, and cause its subsidiaries to conduct their
       respective businesses, only in the ordinary course and in a manner which
       is substantially consistent with past practice;

     - preserve intact its business organizations and goodwill;

     - use commercially reasonable efforts to keep available the services of its
       officers and employees;

     - confer on a regular basis with Equity Office to report material
       operational matters and, except in specified instances, any proposals to
       engage in material transactions;

     - promptly notify Equity Office of any material emergency or other material
       change in its condition, business, properties, assets, liabilities or
       prospects, or of any material governmental complaints, investigations or
       hearings;

     - promptly deliver to Equity Office true and correct copies of any report,
       statement or schedule filed with the SEC;

     - maintain its books and records in accordance with GAAP consistently
       applied, and to not change any of its methods, principles or practices of
       accounting in any material manner, except as required by the SEC,
       applicable law or GAAP; and

     - duly and timely file all reports, tax returns and other documents
       required to be filed with federal, state, local and other authorities,
       subject to extensions permitted by law, provided that Cornerstone
       notifies Equity Office of any extensions and provided that such
       extensions do not adversely affect Cornerstone's status as a qualified
       REIT under the Internal Revenue Code.

     In addition, pending the mergers, each of Cornerstone and Cornerstone
Partnership has agreed that, without Equity Office's prior written consent or
except as otherwise expressly contemplated by the merger agreement, neither
Cornerstone or Cornerstone Partnership nor any of its subsidiaries will, among
other things:

     - make or rescind any express or deemed election relating to taxes unless
       required by law or necessary to preserve Cornerstone's status as a REIT
       or the status of any subsidiary of Cornerstone as a partnership for
       federal income tax purposes or as a qualified REIT subsidiary as defined
       under the Internal Revenue Code, as the case may be;

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<PAGE>   71

     - acquire, enter into any option to acquire, or exercise an option or other
       right or election or enter into any commitment for the acquisition of any
       real property or, except as permitted in the budget approved in writing
       by Equity Office, other transaction involving payments to or by
       Cornerstone in excess of $100,000, except in the ordinary course of its
       office property business, including leasing activities permitted by
       Equity Office approved guidelines;

     - encumber assets, commence construction of or enter into any commitment to
       develop or construct real estate projects, except in the ordinary course
       of its office property business;

     - incur or enter into any commitment to incur additional debt, except for
       working capital under its revolving line(s) of credit and commitments for
       debt specified in the schedules to the merger agreement;

     - modify, amend or terminate, or enter into any commitment to modify, amend
       or terminate, any debt in existence on the date of the merger agreement;

     - amend their organizational documents;

     - make any change in the number of shares of capital stock or units of
       limited partnership interest issued and outstanding, except in specified
       instances;

     - grant options or any other rights or commitments relating to its shares
       of capital stock or units of limited partnership interest, or any
       security convertible into its shares of capital stock or units of limited
       partnership interest, or any security the value of which is measured by
       shares of beneficial interest, or any security subordinated to the claim
       of its general creditors;

     - amend or waive any rights under any options or other stock rights, except
       as provided for in the merger agreement;

     - authorize, declare, set aside or pay any dividend or make any other
       distribution or payment, other than regular quarterly dividends, or
       regular distributions pursuant to the partnership agreement of
       Cornerstone Partnership, or redemptions of Cornerstone Partnership units
       under the partnership agreement of Cornerstone Partnership where solely
       Cornerstone common stock is used, or as necessary to maintain REIT
       status;

     - directly or indirectly redeem, purchase or acquire any shares of capital
       stock or units of partnership interest or any option, warrant or right to
       acquire, or security convertible into, shares of capital stock or units
       of partnership interest of Cornerstone, other than redemptions of
       Cornerstone Partnership units under the partnership agreement of
       Cornerstone Partnership where solely Cornerstone common stock is used,
       other than the use of Cornerstone common stock in connection with
       equity-based employee benefit plans or as necessary to maintain REIT
       status and other than as set forth in the disclosure letter delivered in
       connection with the merger agreement;

     - sell, lease, mortgage, subject to lien or otherwise dispose of any real
       property, except in specified instances;

     - sell, lease, mortgage, subject to lien or otherwise dispose of any
       personal property or intangible property, except in the ordinary course
       of business and as is not material, individually or in the aggregate;

     - make any loans, advances or capital contributions to, or investments in,
       any other person, except in specified instances;

     - enter into any new, or amend or supplement any existing, contract, lease
       or other agreement with WCP Services, Inc.;

     - pay, discharge or satisfy any claims, liabilities or obligations whether
       absolute, accrued, asserted or unasserted, contingent or otherwise,
       except in specified instances;

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<PAGE>   72

     - guarantee the debt of another person, enter into any "keep well" or other
       agreement to maintain any financial statement condition of another person
       or enter into any arrangement having the economic effect of any of the
       foregoing;

     - except in specified instances, enter into any commitment with any
       officer, director or affiliate of Cornerstone or any of its subsidiaries
       or WCP Services, Inc. or any material commitment with any consultant;

     - increase any compensation or enter into or amend any employment agreement
       with any of its officers, directors or employees earning more than
       $100,000 per year, other than as required by any contract or plan or in
       accordance with waivers by employees of benefits under these agreements;

     - adopt any new employee benefit plan or amend any existing plans or
       rights;

     - settle any stockholder derivative or class action claims arising out of
       or in connection with any of the transactions contemplated by the merger
       agreement;

     - change the ownership of any of its subsidiaries or WCP Services, Inc.,
       except in specified instances;

     - accept a promissory note in payment of the exercise price payable under
       any option to purchase shares of Cornerstone common stock;

     - except in specified instances, enter into any oral or written "tax
       protection agreement" that:

      -- has as one of its purposes to permit a person or entity to assert that
         such person or entity could defer federal taxable income that otherwise
         might have been recognized upon a transfer of property to the
         Cornerstone Partnership or any other Cornerstone subsidiary that is
         treated as a partnership for federal income tax purposes, and that (a)
         prohibits or restricts in any manner the disposition of any assets of
         Cornerstone, any Cornerstone subsidiary, including Cornerstone's
         non-controlled subsidiary, (b) requires that Cornerstone, any
         Cornerstone subsidiary or the Cornerstone non-controlled subsidiary
         maintain, or put in place, or replace, indebtedness, whether or not
         secured by one or more of Cornerstone's properties, or (c) requires
         that Cornerstone, any Cornerstone subsidiary or Cornerstone's
         non-controlled subsidiary offer to any person or entity at any time the
         opportunity to guarantee or otherwise assume, directly or indirectly
         (including, without limitation, through a "deficit restoration
         obligation," indemnification agreement or other similar arrangement),
         the risk of loss for federal income tax purposes for indebtedness or
         other liabilities of Cornerstone, any Cornerstone subsidiary or
         Cornerstone's non-controlled subsidiary;

      -- specifies or relates to a method of taking into account book-tax
         disparities under section 704(c) of the Internal Revenue Code with
         respect to one or more assets of Cornerstone or a Cornerstone
         subsidiary; or

      -- requires a particular method for allocating one or more liabilities of
         Cornerstone or any Cornerstone subsidiary under section 752 of the
         Internal Revenue Code.

     - authorize, recommend, propose or announce an intention to do any of the
       foregoing prohibited actions, or enter into any contract, agreement,
       commitment or arrangement to do any of the foregoing prohibited actions.

CONDITIONS TO THE MERGERS

     CONDITIONS TO THE PARTIES' OBLIGATIONS TO EFFECT THE MERGERS

     The obligations of Cornerstone, Cornerstone Partnership, Equity Office and
EOP Partnership to complete the mergers are subject to the satisfaction or,
where permissible, waiver of the following conditions:

     - the approval of the mergers, as applicable, and the merger agreement by
       the affirmative vote of the holders of at least:
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<PAGE>   73

      -- a majority of the outstanding shares of Cornerstone common stock;

      -- a majority of the outstanding Equity Office common shares;

      -- two-thirds of the outstanding shares of Cornerstone preferred stock;

      -- a majority of all limited partner interests in Cornerstone Partnership
         entitled to be cast, in accordance with the partnership agreement of
         Cornerstone Partnership; and

      -- a majority of all partner interests in EOP Partnership, including
         partner interests held by Equity Office.

     - the applicable waiting period under the Hart-Scott-Rodino Antitrust
       Improvements Act of 1976 will have expired or been terminated;

     - the New York Stock Exchange will have approved for listing the Equity
       Office common shares to be issued in the REIT merger and the Equity
       Office common shares reserved for issuance upon redemption of EOP
       Partnership units issued in the partnership merger, subject to official
       notice of issuance;

     - the registration statement on Form S-4 of which the REIT merger proxy
       statement/prospectus forms a part will have become effective and will not
       be the subject of any stop order or proceedings by the SEC seeking a stop
       order;

     - the registration statement on Form S-4 of which this consent
       solicitation/information statement/prospectus forms a part will have
       become effective and will not be the subject of any stop order or
       proceedings by the SEC seeking a stop order;

     - no temporary restraining order, preliminary or permanent injunction or
       other order issued by any court of competent jurisdiction or other legal
       restraint or prohibition preventing the completion of the mergers or any
       of the other transactions contemplated by the merger agreement will be in
       effect; and

     - Equity Office and EOP Partnership will have received all state securities
       or "blue sky" permits and other authorizations necessary to issue the
       Equity Office common shares issuable in the REIT merger and the EOP
       Partnership units issuable in the partnership merger.

     CONDITIONS TO THE OBLIGATIONS OF EQUITY OFFICE AND EOP PARTNERSHIP TO
EFFECT THE MERGERS

     The obligations of Equity Office and EOP Partnership to complete the
mergers are subject to the satisfaction or, where permissible, waiver of the
following conditions:

     - each of the representations and warranties of Cornerstone and Cornerstone
       Partnership contained in the merger agreement, disregarding all
       qualifications and exceptions relating to "materiality" or "material
       adverse effect," will be true and correct as of the date of the merger
       agreement and as of the closing of the mergers:

      -- except to the extent that these representations and warranties are
         expressly limited by their terms to another date, in which case these
         representations and warranties will be true and correct as of that
         other date; and

      -- except where the failure of these representations and warranties to be
         true and correct would not, individually or in the aggregate,
         reasonably be expected to have a material adverse effect on the
         business, properties, assets, financial condition or results of
         operations of Cornerstone and its subsidiaries taken as a whole.

     - Cornerstone and Cornerstone Partnership will have performed in all
       material respects all obligations required to be performed by them under
       the merger agreement at or before the completion of the mergers;

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<PAGE>   74

     - since February 11, 2000, there will have been no material adverse change
       in the business, financial condition or results of operations of
       Cornerstone and its subsidiaries taken as a whole;

     - Equity Office will have received a certificate of an officer of
       Cornerstone certifying to each of the above;

     - Equity Office will have received an opinion, dated as of the closing date
       of the REIT merger:

      -- from counsel to Cornerstone relating to the REIT status of Cornerstone
         and the partnership status of Cornerstone Partnership;

      -- from counsel to Equity Office relating to the REIT status of Equity
         Office; and

      -- from counsel to Equity Office relating to the federal income tax
         treatment of the REIT merger; and

     - each of William Wilson III and John S. Moody will have entered into
       noncompetition and confidentiality agreements.

     CONDITIONS TO THE OBLIGATIONS OF CORNERSTONE AND CORNERSTONE PARTNERSHIP TO
EFFECT THE MERGERS

     The obligations of Cornerstone and Cornerstone Partnership to complete the
mergers are subject to the satisfaction or, where permissible, waiver of the
following conditions:

     - each of the representations and warranties of Equity Office and EOP
       Partnership contained in the merger agreement, disregarding all
       qualifications and exceptions relating to "materiality" or "material
       adverse effect," will be true and correct as of the date of the merger
       agreement and as of the closing of the mergers:

      -- except to the extent that these representations and warranties are
         expressly limited by their terms to another date, in which case these
         representations and warranties will be true and correct as of that
         other date; and

      -- except where the failure of these representations and warranties to be
         true and correct would not reasonably be expected to have a material
         adverse effect on the business, properties, assets, financial condition
         or results of operations of Equity Office and its subsidiaries taken as
         a whole.

     - Equity Office and EOP Partnership will have performed in all material
       respects all obligations required to be performed by them under the
       merger agreement at or before the completion of the mergers;

     - since the date of the merger agreement, there will have been no material
       adverse change in the business, financial condition or results of
       operations of Equity Office and its subsidiaries taken as a whole;

     - Cornerstone will have received a certificate of an officer of Equity
       Office certifying to each of the foregoing;

     - Cornerstone will have received an opinion, dated as of the closing date
       of the mergers:

      -- from counsel to Equity Office relating to the REIT status of Equity
         Office and BeaMetFed, Inc., a Maryland corporation in which EOP
         Partnership currently owns 51.6% of the outstanding stock, and the
         partnership status of EOP Partnership; and

      -- from counsel to Cornerstone relating to the federal income tax
         treatment of the REIT merger.

     - The Equity Office shareholders will have approved the proposed Equity
       Office charter amendment relating to domestically controlled REIT status
       at the Equity Office special meeting; and

     - Equity Office will have delivered to PGGM a certificate to the effect
       that, to Equity Office's knowledge, Equity Office is a
       "domestically-controlled REIT" as defined in the Internal Revenue Code.
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<PAGE>   75

TAX RELATED UNDERTAKINGS OF EOP PARTNERSHIP

     DEFICIT RESTORATION OBLIGATIONS

     Under the merger agreement, EOP Partnership has agreed to amend its
partnership agreement to permit, in limited circumstances, Cornerstone
Partnership unitholders to enter into a deficit restoration obligations with
respect to the EOP Partnership units that they will receive in the partnership
merger. EOP Partnership will amend its partnership agreement to reflect this
commitment and to make appropriate changes to its loss allocation provisions at
or before the time of the partnership merger.

     Before the completion of the partnership merger, a Cornerstone Partnership
unitholder will be able to enter into a deficit restoration obligation with
respect to the EOP Partnership units that it will receive in the partnership
merger in an amount equal to, or, at the individual unitholder's election, less
than, the maximum amount that the Cornerstone Partnership unitholder was
obligated to restore with respect to its Cornerstone Partnership units
immediately prior to the completion of the partnership merger. After the
partnership merger, a former Cornerstone Partnership unitholder generally will
not be permitted to enter into a deficit restoration obligation or increase the
amount of any deficit restoration obligation with respect to its EOP Partnership
units, except under the following circumstances:

     (1) the former Cornerstone Partnership unitholder will have the right to
         increase the amount of its deficit restoration obligation if the
         unitholder had this right under a separate agreement with Cornerstone
         Partnership, and EOP Partnership assumed the obligations of Cornerstone
         Partnership under that agreement as part of the partnership merger;

     (2) the former Cornerstone Partnership unitholders as a group will have the
         right to increase their deficit restoration obligations by an aggregate
         amount of $50 million, which amount will be reduced by any increase in,
         or new, deficit restoration obligations made between February 11, 2000
         and the completion of the partnership merger, but which will not take
         into account the amount of any deficit restoration obligations entered
         into by former Cornerstone Partnership unitholders described in (1)
         above; and

     (3) EOP Partnership may grant, in its sole discretion, a former Cornerstone
         Partnership unitholder's request to increase the amount of an existing
         deficit restoration obligation if the former Cornerstone Partnership
         unitholder demonstrates, to the satisfaction of EOP Partnership, that
         without an increase in the amount of its deficit restoration
         obligation, the former Cornerstone Partnership unitholder would not be
         allocated enough EOP Partnership liabilities under sections 752 and 465
         of the Internal Revenue Code to avoid the recognition of gain, other
         than gain required to be recognized as a result of actual cash
         distributions from EOP Partnership.

     EOP Partnership does not offer any assurance that the deficit restoration
obligations will be effective to defer taxable gain that a former Cornerstone
Partnership unitholder otherwise would recognize either at the time of the
partnership merger or thereafter. Among other things, a deficit restoration
obligation would be effective to defer the recognition of gain only if and to
the extent that EOP Partnership has recourse liabilities outstanding equal to
the amount of the deficit restoration obligation and any similar obligations
undertaken by other unitholders of EOP Partnership. However, EOP Partnership
will not be required to maintain any level of partnership recourse debt or incur
any additional recourse liability even though it will permit Cornerstone
Partnership unitholders to elect before the partnership merger to continue their
current deficit restoration obligations or to increase their deficit restoration
obligations following the partnership merger under (2) or (3) above, except as
may be required in order to meet obligations to former Cornerstone Partnership
unitholders pursuant to the tax protection agreements described in the schedules
to the merger agreement that are being assumed by EOP Partnership.

     A Cornerstone Partnership unitholder that is entitled to enter into a
deficit restoration obligation with respect to the EOP Partnership units that it
will receive in the partnership merger can do so by entering into an agreement
with EOP Partnership establishing the deficit restoration obligation before the
completion of the partnership merger. A Cornerstone Partnership unitholder who
wishes to enter into such an agreement should contact H. Lee Van Boven at (650)
341-5300.
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<PAGE>   76

     For a more detailed discussion regarding the federal income tax
consequences of a deficit restoration obligation entered into at the time of the
partnership merger or at a later time, see "Material Federal Income Tax
Consequences -- Tax Consequences of the Partnership Merger to Cornerstone
Partnership Unitholders That Receive EOP Partnership Units" below.

     DEBT MAINTENANCE AND LOCK-UP AGREEMENTS

     Under the merger agreement, EOP Partnership has agreed to assume the
obligations of Cornerstone Partnership under several agreements with particular
Cornerstone Partnership unitholders with respect to specific properties that
were contributed to Cornerstone Partnership by those Cornerstone Partnership
unitholders, or by entities which were owned by those Cornerstone Partnership
unitholders. Generally, under the agreements assumed from Cornerstone
Partnership, EOP Partnership will be required:

     - with respect to Corporate 500 Centre, to maintain a specified amount of
       "qualified nonrecourse financing" and not to dispose of that property in
       a taxable transaction until the earlier of January 29, 2008 and the date
       on which less than 205,699 units are owned by the unitholders that
       contributed Corporate 500 Centre to Cornerstone Partnership;

     - with respect to One Memorial Drive, not to dispose of that property in a
       taxable transaction until after April 28, 2008;

     - with respect to Wilshire Palisades and 201 California, not to prepay
       specified loans secured by those properties that were in place at the
       time those properties were acquired by Cornerstone Partnership, not to
       dispose of those properties in taxable transactions before the earlier of
       June 3, 2008 or the date on which Cornerstone Partnership gives notice
       that less than 166,566 units are held by unitholders that contributed
       Wilshire Palisades and/or 201 California to Cornerstone Partnership, and
       to use best efforts not to dispose of those properties in taxable
       transactions on or after such date, if adverse tax consequences would
       result to the former Cornerstone Partnership unitholders who originally
       contributed those properties to Cornerstone Partnership;

     - with respect to specified properties acquired by Cornerstone Partnership
       from William Wilson & Associates and related entities in December 1998,
       to maintain a specified amount of recourse indebtedness until after
       December 31, 2009, and, until after December 31, 2009, not to dispose of
       specified properties in taxable transactions and to limit taxable
       dispositions of specified other properties, based on an annual limitation
       on the amount of taxable gain that will be required to be recognized for
       federal income tax purposes by the former Cornerstone Partnership
       unitholders who originally contributed those properties to Cornerstone
       Partnership;

     - with respect to Bixby Ranch, to maintain a level of nonrecourse
       indebtedness at least equal to the then outstanding balance of specified
       nonrecourse indebtedness existing at the time Cornerstone Partnership
       acquired Bixby Ranch through maturity of such existing indebtedness; and

     - with respect to Wells Fargo Center, not to dispose of that property in a
       taxable transaction until after January 21, 2007.

     Generally, as a result of these agreements, EOP Partnership will not be
able to dispose of and/or prepay debt secured by the relevant properties during
the proscribed periods unless EOP Partnership either:

     - obtains the prior written consent of specified former Cornerstone
       Partnership unitholders; or

     - compensates those specified former Cornerstone Partnership unitholders
       for the acceleration of any tax liability incurred by them due to the
       transaction, with any compensation to be paid to a former Cornerstone
       Partnership unitholder under these circumstances to be determined under
       the existing agreement between Cornerstone Partnership and the
       unitholder.

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<PAGE>   77

Therefore, even if it were in the best interest of EOP Partnership to sell, or
prepay debt secured by, any of the properties that are subject to these
agreements, it may be difficult or impossible for EOP Partnership to do so
during the applicable lock-up periods.

     Except for the agreements described above, EOP Partnership has not made any
commitment to Cornerstone Partnership or any of the Cornerstone Partnership
unitholders not to undertake any transactions relating to properties that EOP
Partnership will acquire from Cornerstone Partnership in the partnership merger.

NO SOLICITATION BY CORNERSTONE OR CORNERSTONE PARTNERSHIP

     Cornerstone has agreed, for itself and in its capacity as the sole general
partner of Cornerstone Partnership, that neither it nor any Cornerstone
subsidiary will, nor will any of them permit any officer, director, employee,
affiliate, agent, investment banker, financial advisor, attorney, accountant,
broker, finder, consultant or other agent or representative to:

     - invite, initiate, solicit or encourage, directly or indirectly, any
       inquiries, proposals, discussions or negotiations or the making or
       implementation of any proposal or offer, including any proposal or offer
       to its stockholders, with respect to an "alternative acquisition
       proposal," as defined below;

     - engage in any discussions or negotiations with or provide any
       confidential or non-public information or data to, any person relating
       to, or that may reasonably be expected to lead to, an alternative
       acquisition proposal;

     - enter into any letter of intent, agreement in principle or agreement
       relating to an alternative acquisition proposal;

     - propose publicly to agree to do any of the foregoing; or

     - otherwise facilitate any effort or attempt to make or implement an
       alternative acquisition proposal.

     Cornerstone has agreed, for itself and in its capacity as the sole general
partner of Cornerstone Partnership, that it will:

     - immediately cease and cause to be terminated any existing activities,
       discussions or negotiations with any parties conducted previously with
       respect to any alternative acquisition proposal; and

     - notify Equity Office promptly if Cornerstone or any of its subsidiaries
       receives any such inquiries or proposals, or any requests for such
       information, or if any such negotiations or discussions are sought to be
       initiated or continued with it, and include in such notice the identity
       of the person making such inquiry, proposal or request, the material
       terms of such inquiry, proposal or request and, if in writing, will
       promptly deliver to Equity Office a copy of such inquiry, proposal or
       request along with all other related documentation and correspondence.

     Notwithstanding the foregoing, Cornerstone, including in its capacity as
the sole general partner of Cornerstone Partnership, may furnish information to,
or enter into discussions or negotiations with, any person that makes an
unsolicited bona fide written proposal relating to an alternative acquisition
proposal, if, and only to the extent that:

     - a majority of the board of directors of Cornerstone determines in good
       faith, after consultation with its outside counsel, that such action is
       required for the board of directors of Cornerstone to comply with its
       fiduciary duties to stockholders imposed by applicable law;

     - before furnishing such information to, or entering into discussions or
       negotiations with, such person, Cornerstone provides written notice to
       Equity Office to the effect that it is furnishing information to, or
       entering into discussions with, such person; and

     - Cornerstone enters into a confidentiality agreement with that person on
       terms in the aggregate not more favorable to that person than the terms
       of the confidentiality agreement entered into with Equity Office.
                                       65
<PAGE>   78

     For purposes of the merger agreement, an "alternative acquisition proposal"
means a merger, acquisition, tender offer, exchange offer, transaction resulting
in the issuance of securities representing 10% or more of the outstanding equity
securities of Cornerstone or Cornerstone Partnership, consolidation, business
combination, recapitalization, liquidation, dissolution, share exchange,
business combination, sale, lease, exchange, mortgage, pledge, transfer or other
disposition of 10% or more of the assets or equity securities, including
partnership interests and units, of Cornerstone or Cornerstone Partnership,
other than the mergers.

     Notwithstanding the foregoing, in the event that an alternative acquisition
proposal constitutes a superior alternative acquisition proposal, the board of
directors of Cornerstone may withdraw, modify, amend or qualify its
recommendation of the merger agreement and REIT merger and recommend that
superior alternative acquisition proposal to its stockholders if:

     - Cornerstone complies fully with the foregoing provisions and provides
       Equity Office with at least three business days' prior written notice of
       its intent to withdraw, modify, amend or qualify its recommendation of
       the merger agreement and the REIT merger;

     - during such three business days Equity Office makes a counter proposal to
       such superior alternative acquisition proposal, Cornerstone's board of
       directors in good faith, taking into account the advice of its outside
       financial advisors of nationally recognized reputation, determines that
       the Equity Office counter proposal is:

      -- not at least as favorable to Cornerstone's stockholders as the superior
         alternative acquisition proposal, from a financial point of view; and

      -- not at least as favorable generally to Cornerstone's stockholders,
         taking into account all financial and strategic considerations and
         other relevant factors, including relevant legal, financial, regulatory
         and other aspects of that proposal, and the conditions, prospects and
         time required for completion of that proposal.

     - Cornerstone terminates the merger agreement in accordance with its terms
       and pays to EOP Partnership the termination fee.

     For purposes of the merger agreement, a "superior alternative acquisition
proposal" means a bona fide written proposal made by a third party to acquire,
directly or indirectly, Cornerstone and/or Cornerstone Partnership pursuant to a
tender or exchange offer, merger, share exchange, consolidation or sale of all
or substantially all of the assets of Cornerstone, Cornerstone Partnership, and
their subsidiaries or otherwise:

     - on terms which a majority of the board of directors of Cornerstone
       determines in good faith, taking into account the advice of Cornerstone's
       financial advisors of nationally recognized reputation, are superior,
       from a financial point of view, to Cornerstone's stockholders to those
       provided for in the REIT merger;

     - on terms which a majority of the board of directors of Cornerstone
       determines in good faith to be more favorable generally to Cornerstone's
       stockholders, taking into account all financial and strategic
       considerations and other relevant factors, including relevant legal,
       financial, regulatory and other aspects of such proposals, and the
       conditions, prospects and time required for completion of such proposal;
       and

     - for which financing, to the extent required, is then fully committed and
       capable of being obtained; and

     - which the board of directors of Cornerstone determines in good faith is
       reasonably capable of being consummated.

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<PAGE>   79

TERMINATION OF THE MERGER AGREEMENT

     RIGHT TO TERMINATE

     The merger agreement may be terminated at any time before the completion of
the partnership merger, whether before or after approval of the merger agreement
and the mergers by the Equity Office shareholders, EOP Partnership limited
partners, Cornerstone stockholders or Cornerstone Partnership limited partners,
as follows:

     - by mutual written consent duly authorized by the Equity Office board of
       trustees and the Cornerstone board of directors;

     - by either Equity Office or Cornerstone if:

      -- any judgment, injunction, order, decree or action by any governmental
         entity preventing the consummation of either the REIT merger or the
         partnership merger becomes final and non-appealable;

      -- the REIT merger and the partnership merger have not been completed
         before December 31, 2000; however, neither Equity Office nor
         Cornerstone may terminate the merger agreement if its breach is the
         reason that the mergers have not been completed;

      -- the holders of at least a majority of the outstanding shares of
         Cornerstone common stock and two-thirds of the outstanding shares of
         Cornerstone preferred stock fail to approve the REIT merger and the
         merger agreement at the Cornerstone special meeting, or if holders of a
         majority of the limited partner interests in Cornerstone Partnership
         fail to approve the merger agreement and the REIT merger, but
         Cornerstone may not terminate for either of these reasons if it is in
         breach in any material respect of its obligations contained in the
         merger agreement relating to obtaining the required shareholder and
         partner votes; or

      -- the holders of Equity Office common shares fail to approve the REIT
         merger and the merger agreement at the Equity Office special meeting,
         or holders of a majority of the partner interests in EOP Partnership
         fail to approve the merger agreement and the REIT merger, but Equity
         Office may not terminate for either of these reasons if it is in breach
         in any material respect of its obligations contained in the merger
         agreement relating to obtaining the required shareholder and partner
         votes.

     - by Equity Office:

      -- upon a breach of or failure to perform any representation, warranty,
         covenant, obligation or agreement on the part of Cornerstone or
         Cornerstone Partnership contained in the merger agreement, or if any
         representation or warranty of Cornerstone or Cornerstone Partnership
         becomes untrue, in either case such that the conditions to the
         consummation of the mergers contained in the merger agreement would be
         incapable of being satisfied by December 31, 2000, or as otherwise
         extended by the parties; or

      -- if (a) the Cornerstone board of directors has failed to recommend or
         has withdrawn, modified, amended or qualified, or proposed publicly not
         to recommend or to withdraw, modify, amend or qualify, in any manner
         adverse to Equity Office its approval or recommendation of either of
         the mergers or the merger agreement or approved or recommended any
         superior alternative acquisition proposal, (b) following the
         announcement or receipt of an alternative acquisition proposal,
         Cornerstone has failed to call the Cornerstone special meeting or
         failed to prepare and mail to its stockholders the joint proxy
         statement/prospectus or (c) the Cornerstone board of directors or any
         committee of the Cornerstone board of directors has resolved to do any
         of the foregoing.

                                       67
<PAGE>   80

     - by Cornerstone:

      -- upon a breach of any representation, warranty, covenant obligation or
         agreement on the part of Equity Office or EOP Partnership contained in
         the merger agreement, or if any representation or warranty of Equity
         Office or EOP Partnership becomes untrue, in either case such that the
         conditions to the consummation of the mergers contained in the merger
         agreement would be incapable of being satisfied by December 31, 2000 or
         as otherwise extended by the parties; or

      -- if the Cornerstone board of directors has withdrawn, modified, amended
         or qualified in any manner adverse to Equity Office its approval or
         recommendation of either of the mergers or the merger agreement in
         connection with, or approved or recommended, any superior alternative
         acquisition proposal, or in order to enter into a binding written
         agreement with respect to a superior alternative acquisition proposal,
         so long as, in each case, Cornerstone complied with the terms of the no
         solicitation provisions contained in the merger agreement and, before
         terminating the merger agreement, has paid to EOP Partnership the
         termination fee.

     EFFECT OF TERMINATION

     Except for provisions in the merger agreement regarding confidentiality of
nonpublic information, payment of fees and expenses, the effect of termination
and specified miscellaneous provisions, if the merger agreement is terminated as
described above, the merger agreement will become void and have no effect. In
addition, if the merger agreement is so terminated, there will be no liability
on the part of Equity Office, EOP Partnership, Cornerstone or Cornerstone
Partnership, except to the extent that such termination results from a material
breach by any party of any of its representations, warranties, covenants or
agreements contained in the merger agreement. The confidentiality agreement,
dated January 13, 2000, between Cornerstone and Equity Office will continue in
effect notwithstanding any termination of the merger agreement.

EXPENSES; TERMINATION FEE

     Except as described below, each party to the merger agreement will bear its
own fees and expenses in connection with the transactions contemplated by the
merger agreement.

     Cornerstone and Cornerstone Partnership will pay to EOP Partnership a
termination fee if the merger agreement is terminated:

     - by Cornerstone, (a) if the Cornerstone board of directors has withdrawn,
       modified, amended or qualified in any manner adverse to Equity Office its
       approval or recommendation of either of the mergers or the merger
       agreement in connection with, or approved or recommended, any superior
       alternative acquisition proposal, or (b) in order to enter into a binding
       written agreement with respect to a superior alternative acquisition
       proposal, so long as, in each case, Cornerstone complied with the terms
       of the nonsolicitation provisions contained in the merger agreement;

     - by Equity Office if the Cornerstone board of directors has failed to
       recommend or has withdrawn, modified, amended or qualified, or proposed
       publicly not to recommend or to withdraw, modify, amend or qualify, in
       any manner adverse to Equity Office its approval or recommendation of
       either of the mergers or the merger agreement or approved or recommended
       any superior alternative acquisition proposal, or has resolved to do any
       of the foregoing; or

     - by either party under the circumstances listed below, but only if (a)
       Cornerstone or Cornerstone Partnership has received a proposal for an
       alternative acquisition transaction before such termination and (b)
       before or within 12 months after such termination, Cornerstone or
       Cornerstone Partnership enters into an agreement regarding any
       alternative acquisition transaction that is later completed:

                                       68
<PAGE>   81

      -- Cornerstone breaches any of its representations or warranties in the
         merger agreement, and such breach has a material adverse effect on
         Cornerstone and its subsidiaries taken as a whole and cannot be
         rectified by December 31, 2000;

      -- Cornerstone fails to perform in all material respects all of its
         covenants, obligations or agreements in the merger agreement and such
         failure cannot be rectified by December 31, 2000;

      -- following Cornerstone's receipt or announcement of an alternative
         acquisition proposal, Cornerstone fails to call the Cornerstone special
         meeting or fails to prepare and mail to its stockholders the joint
         proxy statement/prospectus delivered to Cornerstone stockholders
         simultaneously herewith;

      -- any judgment, injunction, order, decree or action by any governmental
         entity of competent authority, which primarily results from any action,
         inaction of Cornerstone, its subsidiaries or its non-controlled
         subsidiary and prevents the consummation of the REIT merger or the
         partnership merger, becomes final and non-appealable;

      -- the REIT merger and the partnership merger are not completed before
         December 31, 2000, and the terminating party has not materially
         breached its obligations under the merger agreement in a way that
         prevents the REIT merger or the partnership merger from being completed
         before December 31, 2000; or

      -- the holders of at least a majority of the outstanding shares of
         Cornerstone common stock and the holders of at least two-thirds of the
         outstanding shares of Cornerstone preferred stock fail to approve the
         REIT merger and the merger agreement at the Cornerstone special
         meeting.

     The termination fee that EOP Partnership may be entitled to receive will be
an amount equal to the lesser of (1) $100 million less termination expenses, as
described below, paid or payable under the merger agreement and (2) the maximum
amount that can be paid to EOP Partnership without causing Equity Office to fail
to meet the REIT income requirements under the Internal Revenue Code.
Cornerstone's and Cornerstone Partnership's obligation to pay any unpaid portion
of the termination fee will terminate on February 11, 2003.

     Cornerstone and Cornerstone Partnership will pay to EOP Partnership
termination expenses if the merger agreement is terminated:

     - by Equity Office, upon a breach of or failure to perform any
       representation, warranty, covenant, obligation or agreement on the part
       of Cornerstone or Cornerstone Partnership contained in the merger
       agreement, or if any representation or warranty of Cornerstone or
       Cornerstone Partnership becomes untrue, in either case such that the
       conditions to the consummation of the mergers contained in the merger
       agreement would be incapable of being satisfied by December 31, 2000, or
       as otherwise extended by the parties, so long as Cornerstone was not
       entitled to terminate the merger agreement because of breach of any
       representation, warranty, covenant, obligation or agreement on the part
       of Equity Office or EOP Partnership; or

     - by either Equity Office or Cornerstone, if the holders of a majority of
       the outstanding shares of Cornerstone common stock and Cornerstone
       preferred stock fail to approve the REIT merger and the merger agreement
       at the Cornerstone special meeting, or if holders of a majority of the
       limited partner interests in Cornerstone Partnership fail to approve the
       merger agreement and the REIT merger, so long as Cornerstone was not
       entitled to terminate the merger agreement because of breach of any
       representation, warranty, covenant, obligation or agreement on the part
       of Equity Office or EOP Partnership.

     Equity Office and EOP Partnership will pay to Cornerstone Partnership
termination expenses if the merger agreement is terminated:

     - by Cornerstone, upon a breach of any representation, warranty, covenant
       obligation or agreement on the part of Equity Office or EOP Partnership
       contained in the merger agreement, or if any

                                       69
<PAGE>   82

       representation or warranty of Equity Office or EOP Partnership becomes
       untrue, in either case such that the conditions to the consummation of
       the mergers contained in the merger agreement would be incapable of being
       satisfied by December 31, 2000 or as otherwise extended by the parties,
       so long as Equity Office was not entitled to terminate the merger
       agreement because of a breach of any representation, warranty, covenant,
       obligation or agreement on the part of Cornerstone or Cornerstone
       Partnership; or

     - by either Cornerstone or Equity Office, if the holders of a majority of
       the outstanding Equity Office common shares fail to approve the REIT
       merger and the merger agreement at the Equity Office special meeting, or
       if holders of a majority of the partner interests in EOP Partnership fail
       to approve the merger agreement and the REIT merger, but neither Equity
       Office nor Cornerstone may terminate for either of these reasons if it is
       in breach in any material respect of its obligations contained in the
       merger agreement relating to obtaining the required shareholder and
       partner votes, so long as Equity Office was not entitled to terminate the
       merger agreement because of breach of any representation, warranty,
       covenant, obligation or agreement on the part of Cornerstone or
       Cornerstone Partnership.

     The termination expenses that EOP Partnership or Cornerstone Partnership
may be entitled to receive will be an amount equal to the lesser of (a)
$7,500,000 or (b) such party's out-of-pocket expenses incurred in connection
with the merger agreement and the transactions contemplated by the merger
agreement, including all attorneys', accountants' and investment bankers' fees
and expenses. If the termination expenses payable to that party exceed the
maximum amount that can be paid to that party without causing that party to fail
to meet the REIT income requirements under the Internal Revenue Code, then the
amount initially payable to that party will be that maximum amount. The paying
party's obligation to pay any unpaid portion of the termination fee will
terminate on February 11, 2003.

     In addition, in the event that Equity Office prevails in a suit for a
breach by Cornerstone and Cornerstone Partnership of their obligation to pay the
termination fee or termination expenses under the merger agreement, Equity
Office will be entitled to its costs and expenses in connection with the suit,
with interest.

WAIVER AND AMENDMENT OF THE MERGER AGREEMENT

     The merger agreement may be amended by the parties in writing by action of
the Equity Office board of trustees and the Cornerstone board of directors at
any time before the filing of the Delaware Certificate of Merger relating to the
partnership merger and the Maryland and Nevada articles of merger relating to
the REIT Merger.

     At any time before the completion of the mergers, the parties may, in
writing:

     - extend the time for the performance of any of the obligations or other
       acts of the other party;

     - waive any inaccuracies in the representations and warranties of the other
       party contained in the merger agreement or in any document delivered
       pursuant to the merger agreement; or

     - waive compliance with any of the agreements or conditions of the other
       party contained in the merger agreement, except as specified.

INDEMNIFICATION; DIRECTORS' AND OFFICERS' INSURANCE

     In the merger agreement, Equity Office and EOP Partnership have agreed to
provide exculpation and indemnification for each person who has been at any time
on or before February 11, 2000, or who becomes before the completion of the
mergers, an officer or director of Cornerstone or any Cornerstone subsidiary.
This exculpation and indemnification will be the same as provided to these
persons by Cornerstone and its subsidiaries immediately before the completion of
the mergers in each entity's respective charter, bylaws, partnership, operating
or similar agreement, as applicable, as in effect on

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February 11, 2000. This exculpation and indemnification covers actions only on
or before the completion of the mergers, including all transactions contemplated
by the merger agreement.

     In addition, Equity Office and EOP Partnership also agreed to indemnify and
hold harmless, to the full extent permitted by applicable law, each of the
persons described above against any losses, claims, liabilities, expenses,
judgments, fines and amounts paid in settlement in connection with any
threatened or actual claim, action, suit, proceeding or investigation, whether
civil, criminal or administrative, including any action by or on behalf of any
or all security holders of Cornerstone or Equity Office, or any of their
subsidiaries, or by or in the right of Cornerstone or Equity Office, or any of
their subsidiaries, in which any of these persons is, or is threatened to be,
made a party based in whole or in part on, or arising in whole or in part out
of, or pertaining to:

     - the fact that he or she is or was an officer, employee or director of
       Cornerstone or any of its subsidiaries or any action or omission by that
       person in his capacity as a director; or

     - the merger agreement or the transactions contemplated by the merger
       agreement, whether in any case asserted or arising before or after the
       completion of the mergers.

     After the completion of the mergers, Equity Office and EOP Partnership will
be obligated to promptly pay and advance reasonable expenses and costs incurred
by each of these persons as they become due and payable in advance of the final
disposition of the claim, action, suit, proceeding or investigation to the
fullest extent and in the manner permitted by law. Equity Office is also
obligated to purchase, at or before the completion of the mergers, directors'
liability insurance policy coverage for Cornerstone's directors and executive
officers for a period of six years which will provide the directors and officers
with coverage on substantially similar terms as currently provided by
Cornerstone to these directors and officers.

VOTING AGREEMENTS

     CORNERSTONE VOTING AGREEMENTS

     Each of the directors and executive officers of Cornerstone, including
their affiliates, and PGGM have entered into voting agreements with Equity
Office and EOP Partnership agreeing to vote all shares of Cornerstone common
stock, and, if applicable, all Cornerstone Partnership units, owned of record by
each of them, or that they otherwise have the power to vote:

     - for adoption and approval of the merger agreement and the mergers, as
       applicable; and

     - against adoption or approval of any action or agreement made or taken in
       opposition to or in competition with the REIT merger or the partnership
       merger, as applicable.

     Each such stockholder also is restricted from soliciting alternative
acquisition proposals with respect to Cornerstone or engaging in any discussions
or negotiations with, or providing any confidential or non-public information
to, any person relating to an alternative acquisition proposal, or otherwise
facilitating any effort or attempt to make or implement an alternative
acquisition proposal.

     As of the record date for the Cornerstone special meeting, these persons
and entities beneficially owned, excluding stock options and Cornerstone
Partnership units held by them,           shares of Cornerstone common stock,
representing      % of the outstanding shares of Cornerstone common stock
entitled to be voted at the Cornerstone special meeting. As of                ,
these persons and entities beneficially owned 5,056,240 Cornerstone Partnership
units, representing 3.4% of the outstanding units of Cornerstone Partnership
entitled to consent to the mergers.

     PGGM Voting Agreement. In addition to the general terms and conditions
applicable to each of the voting agreements, the voting agreement between Equity
Office, EOP Partnership, WCP Services, Inc. and PGGM also provides, among other
things, that:

     - Equity Office will assume Cornerstone's obligations under the amended and
       restated registration rights and voting agreement, dated December 16,
       1998, among Cornerstone, PGGM and Dutch Institutional Holding Company,
       Inc., as amended by the PGGM voting agreement; and
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     - Jan H.W.R. van der Vlist, a current Cornerstone board member, will become
       a trustee of the combined entity, with his term expiring in 2003, and
       Equity Office is obligated to nominate Mr. van der Vlist for reelection
       to the board of trustees in 2003 and 2006 if PGGM and its affiliates
       continue to own at least 21,000,000 of the issued and outstanding Equity
       Office common shares, as adjusted for stock splits or similar actions, at
       all times up to the time the trustees are being elected in those years.
       If Mr. van der Vlist fails to stand for reelection in 2003 or 2006 for
       any reason, or in the event of his death or earlier resignation, and if
       PGGM continues to own at least 21,000,000 of the issued and outstanding
       Equity Office shares as described above, Equity Office is required take
       all action necessary to nominate a replacement designated by PGGM for
       election or reelection as a trustee for an additional three-year term,
       subject to Equity Office's approval if the replacement is not an officer,
       director or employee of PGGM.

     EQUITY OFFICE VOTING AGREEMENTS

     Each of the trustees and executive officers of Equity Office, including
their affiliates, have entered into voting agreements with Cornerstone and
Cornerstone Partnership agreeing to vote all Equity Office common shares, and,
if applicable, all EOP Partnership units, owned of record by each of them, or
that they otherwise have the power to vote:

     - in favor of adoption and approval of the merger agreement, the mergers
       and the other transactions contemplated by the merger agreement; and

     - against approval or adoption of any action or agreement made or taken in
       opposition to or in competition with the REIT merger or the partnership
       merger, as applicable.

     As of the record date for the Equity Office special meeting, these persons
and entities beneficially owned, excluding share options and EOP Partnership
units held by them,                Equity Office common shares, representing
     % of the outstanding Equity Office common shares entitled to be voted at
the Equity Office special meeting.

PREFERRED STOCK OPTION AGREEMENT

     The holders of all of the outstanding shares of Cornerstone preferred stock
have entered into a stock option agreement with Equity Office and Cornerstone.
Under the agreement, these holders have granted to Cornerstone and Equity
Office, respectively, an option to acquire all of their shares of Cornerstone
preferred stock at any time before the completion of the merger at a purchase
price of $18.00 per share, plus accrued and unpaid dividends, in cash, subject
to adjustment as provided in the agreement. If the merger agreement is amended
to increase the purchase price per share in the merger, either before or after
Cornerstone or Equity Office exercises its option under the agreement to
purchase all of their shares of Cornerstone preferred stock, the purchase price
of the Cornerstone preferred stock will be adjusted to equal the purchase price
contained in the amended merger agreement.

AMENDMENTS TO EQUITY OFFICE'S DECLARATION OF TRUST RELATING TO
"DOMESTICALLY-CONTROLLED" REIT STATUS

     Based on the number of Equity Office common shares and shares of
Cornerstone common stock outstanding on the record date, PGGM could own up to
approximately      % of the Equity Office common shares following the merger, if
PGGM elects to convert its Cornerstone common stock into Equity Office common
shares in the merger. In order to assist Equity Office in continuing to qualify
as a domestically-controlled REIT following the merger and as required by the
merger agreement, amendments to the declaration of trust of Equity Office will
be effected as part of the merger. The text of these amendments is attached to
this consent solicitation/information statement/prospectus as Annex D.

     The amendments restrict the direct or indirect acquisition and ownership of
Equity Office shares, if as a result of the acquisition or ownership, non-U.S.
persons would own directly or indirectly 43% or more of the fair market value of
the issued and outstanding Equity Office shares. This ownership restriction
would not apply to any acquisition of Equity Office preferred shares outstanding
at the time the amendments

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<PAGE>   85

become effective, or Equity Office common shares received upon the conversion of
any Equity Office preferred shares. If any transfers of Equity Office shares
occur that would result in non-U.S. persons owning directly or indirectly 43% or
more of the fair market value of the issued and outstanding Equity Office shares
as described above, then the number of shares that would cause a non-U.S. person
to violate this restriction will be automatically transferred to a charitable
trust, or if transfer to a charitable trust would not be effective to prevent
violation of this restriction, then the transfer of shares will be void.

     The board of trustees of Equity Office may increase the ownership
limitation to a percentage not to exceed 49% of the fair market value of the
issued and outstanding Equity Office shares, less the percentage of the
aggregate value of all outstanding shares attributable to the value of any
preferred shares that were issued and outstanding at the time the amendments
become effective or the common shares into which they are convertible. The
amendments also require each person who is a beneficial or constructive owner of
Equity Office shares to provide any information as Equity Office may require, in
good faith, in order to determine Equity Office's status as a
domestically-controlled REIT. There is no guarantee, however, that the
amendments will ensure that Equity Office continues to qualify as a
domestically-controlled REIT.

ACQUISITION OF WCP SERVICES

     William Wilson III and John S. Moody are the owners of common shares of
Cornerstone's third-party service subsidiary, WCP Services, Inc., representing
99% of the voting power and 5% of the economic interests in WCP Services.
Messrs. Wilson and Moody have entered into a stock purchase agreement relating
to such common shares of WCP Services. This agreement provides for the sale of
the voting capital stock of WCP Services owned by Messrs. Wilson and Moody to
Equity Office Properties Management Corp., a Delaware corporation in which
Equity Office owns a 95% non-voting equity interest. Each of Messrs. Wilson and
Moody will receive $200,000, including the assumption of indebtedness, in
exchange for his voting capital stock of WCP Services. WCP Services provides
third party management services, tenant services and development services.

                    MATERIAL FEDERAL INCOME TAX CONSEQUENCES

OVERVIEW

     The following discussion summarizes the material federal income tax
consequences of:

     - the partnership merger, in which Cornerstone Partnership will merge with
       and into EOP Partnership and Cornerstone Partnership unitholders will
       receive 0.7009 of a class A unit of EOP Partnership in exchange for each
       Cornerstone Partnership class A common unit that is not redeemed
       immediately prior to the partnership merger;

     - the ownership and disposition of EOP Partnership class A units;

     - the possible redemption of Cornerstone Partnership class A units for
       shares of Cornerstone common stock immediately prior to the partnership
       merger, at the election of the Cornerstone Partnership unitholder as
       permitted by the merger agreement; and

     - the merger of Cornerstone into Equity Office, which is referred to as the
       REIT merger, and the receipt of cash, Equity Office common shares, or
       both, in the REIT merger by Cornerstone Partnership unitholders who elect
       to redeem some or all of their Cornerstone Partnership class A units for
       Cornerstone common stock prior to the partnership merger and to
       participate in the REIT merger as Cornerstone common stockholders.

     The information in this section is based on the current provisions of the
Internal Revenue Code of 1986, as amended, current, temporary and proposed
Treasury Regulations, the legislative history of the Internal Revenue Code,
current administrative interpretations and practices of the Internal Revenue
Service, including its practices and policies as endorsed in private letter
rulings, which are not binding on the Internal Revenue Service except with
respect to the taxpayer that receives such a ruling, and court

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decisions. However, future legislation, Treasury Regulations, administrative
interpretations and court decisions could significantly change current law or
adversely affect current interpretations of existing law. Changes in the
applicable law could apply retroactively. Neither EOP Partnership nor
Cornerstone Partnership has requested or plans to request any rulings from the
Internal Revenue Service concerning the tax treatment of the partnership merger
or EOP Partnership. Thus, it is possible that the Internal Revenue Service would
challenge the statements in this discussion, which do not bind the Internal
Revenue Service or the courts, and that a court would agree with the Internal
Revenue Service.

     As used in this section, the term "EOP Partnership" refers only to EOP
Operating Limited Partnership and the term "Cornerstone Partnership" refers only
to Cornerstone Properties Limited Partnership. "EOP Partnership unit" refers
only to a class A unit of EOP Partnership and "Cornerstone Partnership unit"
refers only to a class A common unit of Cornerstone Partnership.

     Because this is a summary that is intended to address only the U.S. federal
income tax consequences of the partnership merger, ownership of EOP Partnership
units, and the REIT merger that would apply to all Cornerstone Partnership class
A unitholders, it may not contain all the information that may be important to
you. As you review this discussion, you should keep in mind that:

     - the tax consequences to you may vary depending on your particular tax
       situation, including the circumstances under which you originally
       acquired your Cornerstone Partnership units and subsequent events that
       may have affected your Cornerstone Partnership units;

     - you may be subject to special rules that are not discussed below if you
       are:

      -- a tax-exempt organization;

      -- a broker-dealer;

      -- a non-U.S. person;

      -- a trust;

      -- an estate;

      -- a regulated investment company;

      -- an insurance company; or

      -- otherwise subject to special tax treatment under the Internal Revenue
         Code;

     - this summary does not address any state, local, or non-U.S. tax
       consequences;

     - this summary does not address any tax consequences to non-U.S.
       corporations, non-U.S. partnerships, non-U.S. trusts, non-U.S. estates,
       or individuals who are not taxed as citizens or residents of the United
       States, all of which may be referred to collectively as "non-U.S.
       persons"; and

     - this discussion is not intended to be, and should not be construed as,
       tax advice.

     You are urged to review the following discussion and to consult with your
own tax advisor to determine, among other things, the effect of the partnership
merger and the subsequent ownership and disposition of EOP Partnership units on
your individual tax situation, including any state, local or non-U.S. tax
consequences that may apply to you. In addition, if you are considering an
election to redeem all or any portion of your Cornerstone Partnership units for
Cornerstone common stock prior to the partnership merger so that you may
participate in the REIT merger as a Cornerstone common stockholder, you are
urged to consult with your own tax advisor regarding the effect on your personal
tax situation of the redemption of your Cornerstone Partnership units for
Cornerstone common stock and the subsequent receipt of Equity Office common
shares, cash, or both, in the REIT merger.

     As noted above, this discussion does not address any tax consequences to
Cornerstone Partnership unitholders that are non-U.S. persons. Cornerstone
Partnership believes that none of its unitholders is a

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<PAGE>   87

non-U.S. person for U.S. federal income tax purposes. However, special tax
considerations may apply to a Cornerstone Partnership unitholder that itself is
a U.S. partnership or limited liability company but which has non-U.S. persons
as partners or members with respect to the partnership merger, the redemption of
Cornerstone Partnership units for Cornerstone common stock before the
partnership merger, and the subsequent disposition of Cornerstone common stock
in exchange for cash, Equity Office common shares, or both, in the REIT merger.
For example, the partnership merger, a redemption of Cornerstone Partnership
units, and the REIT merger could give rise to "effectively connected income"
with respect to which a Cornerstone Partnership unitholder that is a partnership
with non-U.S. partners would be subject to withholding requirements under
section 1446 of the Internal Revenue Code. However, a Cornerstone Partnership
unitholder that is a partnership will not be required to withhold as a result of
the partnership merger if, due to a nonrecognition provision of the Internal
Revenue Code, the exchange of its Cornerstone Partnership units for EOP
Partnership units does not give rise to any taxable "effectively connected" gain
that is allocable under its partnership agreement to its non-U.S. partners. In
order to avoid withholding and ensure that the nonrecognition provisions of the
Internal Revenue Code apply to the partnership merger, the partnership and its
non-U.S. partners will be required to comply with Internal Revenue Service
reporting requirements. Accordingly, any Cornerstone Partnership unitholder that
is a partnership or limited liability company and whose partners or members
include non-U.S. persons should consult with its own tax advisor regarding any
special U.S. tax consequences to it and its partners or members that may result
from these transactions.

SUMMARY OF THE MATERIAL FEDERAL INCOME TAX CONSEQUENCES OF THE PARTNERSHIP
MERGER

     The partnership merger will be treated for federal income tax purposes as:

     - a contribution by Cornerstone Partnership of all of its assets, subject
       to all of its existing liabilities, to EOP Partnership in exchange for
       EOP Partnership units; and

     - the subsequent distribution of those EOP Partnership units to the
       Cornerstone Partnership unitholders in liquidation of Cornerstone
       Partnership.

     A Cornerstone Partnership unitholder who receives only EOP Partnership
units in exchange for all of its Cornerstone Partnership units in the
partnership merger generally will not recognize taxable gain or loss at the time
of the partnership merger unless the Cornerstone Partnership unitholder receives
or is considered to receive, in connection with the partnership merger, either a
cash distribution or a deemed cash distribution resulting from relief from
liabilities that exceeds the aggregate adjusted basis that the Cornerstone
Partnership unitholder has in its EOP Partnership units received in the
partnership merger, or is otherwise required to recognize ordinary income under
the "at-risk recapture" rules.

     The determination of whether a Cornerstone Partnership unitholder has
received a deemed cash distribution resulting from relief from liabilities
depends on the unitholder's unique circumstances, including:

     - the unitholder's adjusted tax basis in its Cornerstone Partnership units
       at the time of the partnership merger;

     - the assets originally contributed to Cornerstone Partnership by the
       unitholder or by an entity from which the unitholder received its
       Cornerstone Partnership units;

     - the indebtedness, at the time of the partnership merger, of Cornerstone
       Partnership secured by the assets originally contributed by the
       unitholder or by an entity from which the unitholder received its
       Cornerstone Partnership units;

     - Cornerstone Partnership's tax basis at the time of the partnership merger
       in the assets originally contributed by the unitholder or by an entity
       from which the unitholder received its Cornerstone Partnership units;

     - the share of the "unrealized gain" with respect to Cornerstone
       Partnership's assets attributable to the unitholder at the time of the
       partnership merger;
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<PAGE>   88

     - the amount of any recourse liabilities of Cornerstone Partnership
       included in the unitholder's basis by reason of indemnification or
       "deficit restoration" obligations that will be eliminated in the
       partnership merger; and

     - whether a unitholder that has a share of recourse liabilities of
       Cornerstone Partnership by reason of an indemnification or deficit
       restoration obligation elects to enter into a deficit restoration
       obligation with respect to EOP Partnership at the time of the partnership
       merger and whether that deficit restoration obligation is respected for
       federal income tax purposes.

     Even if a Cornerstone Partnership unitholder does not recognize taxable
gain at the time of the partnership merger, the occurrence of subsequent events
could cause the unitholder to recognize all or part of the gain that was
deferred either through the original contribution of assets to Cornerstone
Partnership or through the partnership merger. Equity Office, which is the
general partner of EOP Partnership, generally is not required to take into
account the tax consequences to, or obtain the consent of, the limited partners
of EOP Partnership in deciding whether to cause EOP Partnership to undertake
specific transactions that could have adverse tax consequences to the EOP
Partnership unitholders. However, under the merger agreement, Equity Office and
EOP Partnership have agreed not to undertake specific transactions involving
several specific properties that will be acquired from Cornerstone Partnership
in the partnership merger unless EOP Partnership either:

     - obtains the prior written consent of specified former Cornerstone
       Partnership unitholders; or

     - compensates those specified former Cornerstone Partnership unitholders
       for the acceleration of any tax liability incurred by them due to the
       transaction, with any compensation to be paid to a former Cornerstone
       Partnership unitholder under these circumstances to be determined under
       the existing agreement between Cornerstone Partnership and the
       unitholder.

See "The Merger Agreement -- Tax Related Undertakings of EOP Partnership -- Debt
Maintenance and Lock-up Agreements." Except for these specific commitments, EOP
Partnership and Equity Office have not made any commitment to Cornerstone,
Cornerstone Partnership or any of the Cornerstone Partnership unitholders not to
undertake transactions that will cause the former Cornerstone Partnership
unitholders to recognize all or part of the taxable gain that was deferred
either through the original contribution of assets to Cornerstone Partnership or
through the partnership merger.

TAX STATUS OF EOP PARTNERSHIP

     An entity that is classified as a partnership for federal income tax
purposes generally is not a taxable entity and incurs no federal income tax
liability. Instead, each partner is required to take into account its allocable
share of income, gains, losses, deductions and credits of the partnership in
computing its federal income tax liability, even if no cash distributions are
made by the partnership to the partner. Distributions of money by a partnership
to a partner generally are not taxable unless the amount of the distribution
exceeds the partner's adjusted basis in its partnership interest.

     The obligations of Cornerstone and Cornerstone Partnership to consummate
the partnership merger are conditioned upon their receipt of an opinion of Hogan
& Hartson L.L.P., counsel to Equity Office and EOP Partnership, to the effect
that EOP Partnership has been during and since 1997, and continues to be,
treated for federal income tax purposes as a partnership and not as a
corporation. This opinion will rely on customary factual assumptions and
customary representations made by Equity Office and EOP Partnership. If any of
the factual assumptions or representations relied upon by counsel is inaccurate,
the opinion may not accurately describe the treatment of EOP Partnership as a
partnership for federal income tax purposes.

     Under the Treasury Regulations under section 7701 of the Internal Revenue
Code, an entity that is organized under state law as a partnership that is not a
"publicly traded partnership" will be treated as a partnership for tax purposes
unless it elects to be treated as a corporation. EOP Partnership has not
elected, and will not elect, to be treated as a corporation.

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     An entity that is classified as a partnership under these regulations
nevertheless will be taxable as a corporation if it is a "publicly traded
partnership" within the meaning of section 7704 of the Internal Revenue Code
that fails to satisfy a "90% qualifying income" test under section 7704 of the
Internal Revenue Code. A partnership is a publicly traded partnership under
section 7704 of the Internal Revenue Code if:

     - interests in the partnership are traded on an established securities
       market; or

     - interests in the partnership are readily tradable on a "secondary
       market," or the "substantial equivalent" of a secondary market.

     Under the relevant Treasury Regulations, interests in a partnership will
not be considered readily tradable on a secondary market or on the substantial
equivalent of a secondary market if the partnership qualifies for specified
"safe harbors," which look to the specific facts and circumstances relating to
the partnership and to transfers of interests in the partnership.

     EOP Partnership currently takes the reporting position for federal income
tax purposes that it is not a publicly traded partnership. There is a
significant risk, however, that the right of EOP Partnership unitholders to
redeem the EOP Partnership units for EOP common shares could cause EOP
Partnership units to be considered readily tradable on the substantial
equivalent of a secondary market. Moreover, if EOP Partnership units were
considered to be tradable on the substantial equivalent of a secondary market
either now or in the future, EOP Partnership cannot guarantee that it would
qualify for any of the safe harbors mentioned above or that, if it currently
qualifies for a safe harbor, EOP Partnership will continue to qualify for the
safe harbors in the future. For example, EOP Partnership cannot satisfy the
"private placement" safe harbor because it has more than 100 partners and has
issued units in registered offerings, such as the units to be issued in
connection with the partnership merger.

     If EOP Partnership is a publicly traded partnership, it will not be taxed
as a corporation if at least 90% of its gross income consists of "qualifying
income" under section 7704 of the Internal Revenue Code. Qualifying income
generally includes real property rents and certain other types of passive
income. EOP Partnership believes that it has and will continue to have
sufficient qualifying income so that it will be taxed as a partnership, even if
it were a publicly traded partnership. The income requirements applicable to
Equity Office in order for it to qualify as a REIT under the Internal Revenue
Code and the definition of qualifying income under the publicly traded
partnership rules are very similar. In addition, failure of EOP Partnership to
qualify as a partnership for tax purposes would cause Equity Office to fail to
qualify as a REIT. Therefore, it is likely that Equity Office will manage EOP
Partnership in such a way that Equity Office will meet the gross income tests
applicable to REITs and EOP Partnership will have qualifying income sufficient
for it to avoid being taxed as a corporation.

     If EOP Partnership were a publicly traded partnership, but were not taxed
as a corporation for federal income tax purposes because it satisfies the 90%
qualifying income requirement, EOP Partnership unitholders would be subject to
special passive loss rules applicable to publicly traded partnerships. In
particular, if EOP Partnership were a publicly traded partnership, an EOP
Partnership unitholder would be unable to use passive losses from other passive
activities to offset the unitholder's share of EOP Partnership income and gains.
Similarly, any EOP Partnership losses allocable to an EOP Partnership unitholder
could be used only to offset the unitholder's allocable share of EOP Partnership
income and gains and not against income and gains from other passive activities.

     This entire discussion assumes that EOP Partnership will be treated as a
partnership for federal income tax purposes, in accordance with the opinion of
Hogan & Hartson L.L.P. referred to above. If EOP Partnership were instead
taxable as a corporation, most, if not all, of the tax consequences described
below would not apply and distributions to EOP Partnership unitholders could be
materially reduced. In addition, if EOP Partnership were taxable as a
corporation, Equity Office would fail to qualify as a real estate investment
trust under the Internal Revenue Code and would be taxable as a regular
corporation. This would likely have the effect of reducing the value of Equity
Office common shares, which would

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adversely affect the value of EOP Partnership units because the EOP Partnership
units are convertible into Equity Office common shares or their cash equivalent,
at the election of Equity Office.

TAX STATUS OF CORNERSTONE PARTNERSHIP

     The obligations of Equity Office and EOP Partnership to consummate the
partnership merger are conditioned upon their receipt of an opinion of King &
Spalding, counsel to Cornerstone and Cornerstone Partnership, to the effect that
Cornerstone Partnership has been during and since December 23, 1997, and
continues to be, treated for federal income tax purposes as a partnership and
not as a corporation. This opinion will rely on customary factual assumptions
and customary representations made by Cornerstone and Cornerstone Partnership.
If any of the factual assumptions or representations relied upon by counsel is
inaccurate, the opinion may not accurately describe the treatment of Cornerstone
Partnership as a partnership for federal income tax purposes.

     Under the applicable Treasury Regulations, Cornerstone Partnership will be
classified as a partnership so long as it does not elect to be classified as a
corporation and is not a publicly traded partnership. Cornerstone Partnership
has not elected to be classified as a corporation and currently takes the
reporting position for federal income tax purposes that it is not a publicly
traded partnership. Moreover, Cornerstone Partnership believes that even if it
were a publicly traded partnership, it would not be taxed as a corporation
because at least 90% of its gross income consists of "qualifying income" under
section 7704 of the Internal Revenue Code. See "-- Tax Status of EOP
Partnership" above for a more detailed discussion of the tax consequences of
partnership classification, the publicly traded partnership rules and the
qualifying income exception.

     The discussions under the headings "-- Tax Consequences of the Partnership
Merger to Cornerstone Partnership Unitholders that Receive EOP Partnership
Units" and "-- Tax Consequences of the Redemption of Cornerstone Partnership
Units for Cornerstone Common Stock" assume that Cornerstone Partnership will be
treated as a partnership for federal income tax purposes, in accordance with the
opinion of King & Spalding referred to above. If Cornerstone Partnership were
instead taxable as a corporation, most, if not all, of the tax consequences
described in the relevant discussions below would not apply.

TAX CONSEQUENCES OF THE PARTNERSHIP MERGER TO CORNERSTONE PARTNERSHIP
UNITHOLDERS THAT RECEIVE EOP PARTNERSHIP UNITS

     As described above, the partnership merger will be treated for federal
income tax purposes as if Cornerstone Partnership contributed all of its assets
to EOP Partnership, subject to the existing liabilities of Cornerstone
Partnership, in exchange for EOP Partnership units, followed by a liquidation of
Cornerstone Partnership and a distribution of the EOP Partnership units to the
Cornerstone Partnership unitholders.

     Under section 721 of the Internal Revenue Code, a partnership and its
partners will not recognize gain or loss due to the contribution of property to
the partnership in exchange for an interest in the partnership. In addition,
under section 731 of the Internal Revenue Code, a partner will not have taxable
gain on a distribution from a partnership of property other than "money." For
these purposes, "money" would include a distribution of "marketable securities"
in some circumstances. Section 721 ordinarily applies even when the transferred
property is subject to liabilities, so long as the assumption of liabilities
does not result in a deemed cash distribution to the partner in excess of the
partner's basis in the assets contributed to the partnership. Generally, under
these rules, neither Cornerstone nor a Cornerstone Partnership unitholder will
recognize gain if it only receives EOP Partnership units in the partnership
merger. However, even if a Cornerstone Partnership unitholder receives only EOP
Partnership units in the partnership merger, the unitholder could recognize gain
if one or more of the following situations applies:

     - The unitholder receives a deemed cash distribution from EOP Partnership
       as a result of a decrease in the unitholder's share of Cornerstone
       Partnership liabilities that is not offset by an increase in the
       unitholder's share of EOP Partnership liabilities attributable to the EOP
       Partnership units acquired

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       in the partnership merger. Under these circumstances, the unitholder will
       recognize gain if the deemed cash distribution exceeds the unitholder's
       adjusted basis in its EOP Partnership units received in the partnership
       merger. Similarly, gain could also be recognized by a Cornerstone
       Partnership unitholder if the unitholder's share of EOP Partnership
       liabilities is decreased after the partnership merger, whether the
       decrease is due to the repayment by EOP Partnership of all or part of its
       liabilities or some other event.

     - The contribution of assets by Cornerstone Partnership to EOP Partnership
       is treated in whole or in part as a "disguised sale" of the Cornerstone
       Partnership assets under section 707 of the Internal Revenue Code.

     - The unitholder is considered to receive a taxable distribution of
       "marketable securities" under section 731(c) of the Internal Revenue Code
       to which an exception does not apply.

     - The unitholder is required to recognize income under the recapture rules
       of section 465(e) of the Internal Revenue Code.

     These potential gain recognition situations are discussed more fully below.

     In addition, as mentioned above, subsequent events or transactions could
cause a Cornerstone Partnership unitholder to recognize all or part of its
deferred gain that is not recognized in the partnership merger. See "-- Effect
of Subsequent Events" below.

     Reduction in Share of Partnership Liabilities/Deemed Cash Distribution. If
a Cornerstone Partnership unitholder's share of Cornerstone Partnership
liabilities is reduced as a result of the partnership merger, the unitholder
will be considered to receive a deemed cash distribution in connection with the
partnership merger and, accordingly, the Cornerstone Partnership unitholder
could recognize taxable gain at the time of the partnership merger. The
Cornerstone Partnership unitholder, however, will recognize gain only to the
extent that the deemed cash distribution exceeds the Cornerstone Partnership
unitholder's adjusted tax basis in the EOP Partnership units the unitholder
receives in the partnership merger.

     In order to determine whether a Cornerstone Partnership unitholder's share
of liabilities is reduced as a result of the partnership merger, the Cornerstone
Partnership unitholder's share of liabilities in Cornerstone Partnership
immediately before the partnership merger will be compared to the unitholder's
share of liabilities as an EOP Partnership unitholder immediately after the
partnership merger. Any reduction in a unitholder's share of liabilities will be
considered to result in a deemed cash distribution from EOP Partner ship, which
will be taxable to the extent that it exceeds the Cornerstone Partnership
unitholder's adjusted tax basis in the EOP Partnership units the unitholder
receives in the partnership merger.

     Under section 752 of the Internal Revenue Code and the relevant Treasury
Regulations, the determination of a partner's share of partnership liabilities
depends on whether the liabilities are "recourse" or "non-recourse." A
partnership liability is a recourse liability to the extent that any partner, or
a person related to any partner, bears the economic risk of loss for that
liability. A partnership liability is nonrecourse to the extent that no partner,
and no person related to any partner, bears the economic risk of loss for that
liability.

  Recourse Liabilities

     A former Cornerstone Partnership unitholder will not have any share of the
recourse liabilities of EOP Partnership unless, and only to the extent that, the
unitholder enters into a "deficit restoration obligation" with respect to any
deficit in its capital account as an EOP Partnership unitholder and that deficit
restoration obligation is effective for federal income tax purposes to cause the
former Cornerstone Partnership unitholder to be considered to bear the risk of
loss with respect to EOP Partnership recourse liabilities. Before the completion
of the partnership merger, a Cornerstone Partnership unitholder will be
permitted to enter into a deficit restoration obligation with respect to the EOP
Partnership units that it will receive in the partnership merger in an amount
equal to, or, at the individual unitholder's election, less

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than, the maximum amount that the Cornerstone Partnership unitholder was
obligated to restore with respect to its Cornerstone Partnership units
immediately prior to the partnership merger. After the partnership merger, a
former Cornerstone Partnership unitholder generally will not be permitted to
enter into a deficit restoration obligation or increase the amount of any
deficit restoration obligation with respect to its EOP Partnership units, except
under the following circumstances:

          (1) the former Cornerstone Partnership unitholder will have the right
              to increase the amount of its deficit restoration obligation if
              the unitholder had this right under a separate agreement with
              Cornerstone Partnership, and EOP Partnership assumed the
              obligations of Cornerstone Partnership under that agreement as
              part of the partnership merger;

          (2) the former Cornerstone Partnership unitholders as a group will
              have the right to increase their deficit restoration obligations
              by an aggregate amount of $50 million, which amount will be
              reduced by any increase in, or new, deficit restoration
              obligations undertaken between February 11, 2000 and the
              completion of the partnership merger, but which will not take into
              account the amount of any deficit restoration obligations entered
              into by former Cornerstone Partnership unitholders described in
              (1) above; and

          (3) EOP Partnership may grant, in its sole discretion, a former
              Cornerstone Partnership unitholder's request to increase the
              amount of an existing deficit restoration obligation if the former
              Cornerstone Partnership unitholder demonstrates, to the
              satisfaction of EOP Partnership, that without an increase in the
              amount of its deficit restoration obligation, the former
              Cornerstone Partnership unitholder would not be allocated enough
              EOP Partnership liabilities under sections 752 and 465 of the
              Internal Revenue Code to avoid the recognition of gain, other than
              gain required to be recognized as a result of actual cash
              distributions from EOP Partnership.

     The deficit restoration obligation is an undertaking to restore to EOP
Partnership the amount of any negative capital account balance upon liquidation
or redemption of the unitholder's interest in EOP Partnership, up to the maximum
amount specified in the unitholder's deficit restoration obligation. The
partnership agreement of EOP Partnership allocates net losses in excess of EOP
Partnership's aggregate capital first to Equity Office, in an amount equal to
the excess of the aggregate recourse debt of EOP Partnership over the aggregate
deficit restoration obligations of all EOP Partnership unitholders, and then to
those unitholders who have deficit restoration obligations in proportion to and
to the extent of such restoration amounts. These special allocations of loss
will be made applicable to Cornerstone Partnership unitholders who enter into
deficit restoration obligations with respect to the EOP Partnership units
received in the partnership merger. For a more detailed discussion of
allocations of income and loss under the partnership agreement of EOP
Partnership, see "-- Tax Consequences of Ownership of EOP Partnership Units
After the Partnership Merger -- Allocations of EOP Partnership Income, Gain,
Loss and Deductions" below.

     EOP Partnership does not offer any assurance that the deficit restoration
obligations will be effective to defer taxable gain that a former Cornerstone
Partnership unitholder otherwise would recognize either at the time of the
partnership merger or thereafter. Among other things, a deficit restoration
obligation would be effective to defer the recognition of gain only if and to
the extent that EOP Partnership has recourse liabilities outstanding equal to
the aggregate amount of the deficit restoration obligation of the particular
unitholder and all similar obligations undertaken by other unitholders of EOP
Partnership. However, EOP Partnership will not be required to maintain any
specific level of partnership recourse debt or incur any additional recourse
liabilities in order to permit Cornerstone Partnership unitholders to be
allocated recourse liabilities of EOP Partnership equal to the amount of their
deficit restoration obligations, except as may be required in order to meet
obligations to former Cornerstone Partnership unitholders pursuant to the
protection agreements described in schedules to the merger agreement and being
assumed by EOP Partnership.

     EOP Partnership will take the position for federal income tax reporting
purposes that each former Cornerstone Partnership unitholder that enters into a
deficit restoration obligation, either at the time of the partnership merger or
at a later time, will be allocated a share of EOP Partnership recourse
liabilities

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<PAGE>   93

equal to the lesser of the amount of the unitholder's deficit restoration
obligation or the percentage of all EOP Partnership recourse liabilities that
the amount of the former Cornerstone Partnership unitholder's deficit
restoration obligation bears to the aggregate amount of the deficit restoration
obligations and similar undertakings of all EOP Partnership unitholders and
other partners. The Internal Revenue Service is not bound by such position,
however, and could assert that recourse liabilities should be allocated in a
different manner. EOP Partnership cannot guaranty that the Internal Revenue
Service would not successfully challenge EOP Partnership's position.

     Each Cornerstone Partnership unitholder who has entered into a deficit
restoration obligation with respect to its Cornerstone Partnership units is
urged to consult with its own tax advisor regarding the desirability of entering
into a deficit restoration obligation with respect to the EOP Partnership units
that it will receive in the partnership merger.

  Nonrecourse Liabilities

     A partner's share of partnership nonrecourse liabilities equals the sum of:

     - the partner's share of "partnership minimum gain" under section 704(b) of
       the Internal Revenue Code and the relevant Treasury Regulations;

     - the partner's "section 704(c) minimum gain," which is the amount of any
       taxable gain that would be allocated to the partner under section 704(c)
       of the Internal Revenue Code or in the same manner as section 704(c) of
       the Internal Revenue Code in connection with a revaluation of partnership
       property if the partnership disposed of all partnership property subject
       to one or more nonrecourse liabilities of the partnership in full
       satisfaction of those liabilities and for no other consideration in a
       taxable transaction; and

     - the partner's share of "excess nonrecourse liabilities" that are not
       allocable to the partners under one of the two preceding rules.

     Immediately after the partnership merger, EOP Partnership will not have any
partnership minimum gain, and, thus, no EOP Partnership unitholder will be
allocated any share of nonrecourse debt that is attributable to partnership
minimum gain.

     The amount of any liabilities attributable to section 704(c) minimum gain
allocable to a Cornerstone Partnership unitholder who becomes an EOP Partnership
unitholder will depend on several factors, including:

     - the Cornerstone Partnership unitholder's share of the section 704(c) gain
       of Cornerstone Partnership immediately prior to the partnership merger,
       which depends, among other things, upon the assets that the unitholder
       originally contributed or was deemed to contribute to Cornerstone
       Partnership in exchange for its Cornerstone Partnership units, the tax
       basis of those assets at the time of the contribution to Cornerstone
       Partnership relative to their fair market value at the time, and the
       amount of nonrecourse liabilities of Cornerstone Partnership secured by
       those assets at the time of the partnership merger;

     - the Cornerstone Partnership unitholder's share of any additional 704(c)
       minimum gain attributable to the assets of Cornerstone Partnership
       created by reason of the partnership merger, if, for example, the
       nonrecourse liabilities secured by particular Cornerstone Partnership
       assets at the time of the partnership merger exceed the tax basis of
       those assets by more than the existing section 704(c) minimum gain
       attributable to those assets immediately prior to the partnership merger;
       and

     - the extent to which EOP Partnership causes nonrecourse liabilities as to
       which there exists section 704(c) minimum gain immediately prior to the
       partnership merger to be repaid or refinanced in connection with the
       partnership merger in a manner that reduces or eliminates that section
       704(c) minimum gain.

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<PAGE>   94

     EOP Partnership will allocate any excess nonrecourse liabilities by taking
into account various facts and circumstances relating to its unitholders'
interests in the taxable profits of EOP Partnership, including the unitholder's
allocable share of taxable gain specially allocated under section 704(c) of the
Internal Revenue Code, rather than solely based upon the percentage ownership
interests in EOP Partnership. With respect to former Cornerstone Partnership
unitholders, EOP Partnership will not allocate to them less nonrecourse
liabilities than would be allocated to them if EOP Partnership used the
allocation method previously used by Cornerstone Partnership. This method of
allocation of excess nonrecourse liabilities may result in an allocation of a
greater share of the excess nonrecourse liabilities of EOP Partnership to the
Cornerstone Partnership unitholders who become EOP Partnership unitholders in
the partnership merger and who have "negative capital accounts" than would
result if EOP Partnership merely were to allocate excess nonrecourse liabilities
in accordance with the unitholders' percentage ownership interest in EOP
Partnership. EOP Partnership cannot guarantee, however, that the Internal
Revenue Service will respect these methods of allocation of excess nonrecourse
liabilities following the partnership merger. These methods also could result in
changes from year to year in an EOP Partnership unitholder's share of excess
nonrecourse liabilities of EOP Partnership.

     A former Cornerstone Partnership unitholder who is deemed to receive a cash
distribution from EOP Partnership as a result of a reduction of its share of
liabilities in connection with the partnership merger will recognize taxable
gain equal to the amount by which the deemed cash distribution exceeds the
unitholder's "initial basis" in its EOP Partnership units received in the
partnership merger. A Cornerstone Partnership unitholder's initial basis in the
EOP Partnership units received in the merger will equal the unitholder's
aggregate basis in its Cornerstone Partnership units at the time of the
partnership merger, before taking into account any deemed cash distribution from
EOP Partnership occurring as a result of the partnership merger.

     EOP Partnership cannot guarantee that the nonrecourse liabilities of EOP
Partnership will be allocated in an amount such that no Cornerstone Partnership
unitholder will be deemed to receive a cash distribution in the partnership
merger in excess of the unitholder's basis in its EOP Partnership units received
in the partnership merger. Hence, it is essential that each Cornerstone
Partnership unitholder consult with its own tax advisor and take into account
its own particular circumstances in order to assess the potential impact of a
reduction of the unitholder's partnership liabilities and the resulting deemed
receipt of a cash distribution as a result of the partnership merger.

     Disguised Sale. A Cornerstone Partnership unitholder may have taxable gain
if the partnership merger is considered to result in a "disguised sale" to EOP
Partnership of some or all of either the assets of Cornerstone Partnership or
the Cornerstone Partnership unitholder's units. Section 707 of the Internal
Revenue Code and the applicable Treasury Regulations, which are referred to as
the disguised sale regulations, generally provide that a disguised sale of
property has occurred if:

     - a partner contributes property to a partnership; and

     - the partnership transfers money or other consideration to the partner.

     Under the disguised sale regulations, a contribution to a partnership and
any transfer to a partner that occur within two years of each other are presumed
to be a disguised sale unless:

     - the facts and circumstances clearly establish that the contribution and
       transfer do not constitute a disguised sale; or

     - an exception to disguised sale treatment applies.

     There previously was no authority applying the disguised sale regulations
to a transaction, such as the partnership merger, in which a partnership is
deemed to transfer property to another partnership in exchange for partnership
interests and the transferor partnership is deemed to liquidate. For example, it
was not clear whether the Internal Revenue Service would treat any transfer of
money or other consideration from EOP Partnership to a former Cornerstone
Partnership unitholder that is considered part of a disguised sale as being made
to Cornerstone Partnership and then distributed by Cornerstone

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<PAGE>   95

Partnership to the Cornerstone Partnership unitholder, as opposed to being made
directly to the Cornerstone Partnership unitholder. If the transfer was
considered to be to Cornerstone Partnership, the gain recognized on the
disguised sale would be determined by reference to the excess of the value of
the Cornerstone Partnership assets over the Cornerstone Partnership's basis in
those assets. In addition, the allocation to the Cornerstone Partnership
unitholders of taxable gain of Cornerstone Partnership could be determined under
the allocation provisions of the partnership agreement of Cornerstone
Partnership, with the result that each Cornerstone Partnership unitholder could
be allocated a share of the resulting gain, even if the money or other
consideration giving rise to disguised sale treatment is only received by other
unitholders.

     The Treasury Department, however, has recently proposed regulations that
would permit the parties to a partnership merger to treat any transfers of cash
or other property made by the acquiring partnership to some but not all partners
in the acquired partnership as a direct transaction between the acquiring
partnership and the those individual partners, rather than between the acquiring
partnership and the acquired partnership. Under this approach, only the
Cornerstone Partnership unitholders receiving cash or property other than EOP
Partnership units in the partnership merger would be adversely affected by the
disguised sale regulations. There can be no assurance that these proposed
Treasury Regulations will be adopted in their current form or at all, and even
if adopted, they would be effective only for partnership mergers occurring after
the date of adoption. Nevertheless, absent clear authority to the contrary, EOP
Partnership plans to take the position that any receipt or deemed receipt of
cash or other property by a particular Cornerstone Partnership unitholder in, or
in connection with, the partnership merger does not adversely affect other
Cornerstone Partnership unitholders who receive only EOP Partnership units in
the partnership merger.

     EOP Partnership will not make a direct transfer of money or of
consideration other than EOP Partnership units either to Cornerstone Partnership
or to any Cornerstone Partnership unitholder in the partnership merger. However,
the disguised sale rules can apply in other circumstances as well.

     For purposes of the disguised sale rules, either an assumption of
liabilities by the partnership or a transfer of properties subject to
liabilities is treated as a transfer of money or other property from the
partnership to the partner which may give rise to a disguised sale, even if that
transaction would not otherwise result in a taxable deemed cash distribution in
excess of the partner's basis. However, in connection with a contribution to a
partnership that is not otherwise treated as part of a disguised sale, neither
the assumption of "qualified liabilities" by the partnership nor the acquisition
by the partnership of properties subject to "qualified liabilities" is treated
as part of a disguised sale. Under the disguised sale regulations, a qualified
liability includes:

     - any liability incurred more than two years prior to the earlier of the
       transfer of the property or the date the partner agrees in writing to the
       transfer, as long as the liability has encumbered the transferred
       property throughout the two-year period;

     - a liability that was not incurred in anticipation of the transfer of the
       property to a partnership, but that was incurred by the partner within
       the two-year period prior to the earlier of the date the partner agrees
       in writing to transfer the property or the date the partner transfers the
       property to a partnership and that has encumbered the transferred
       property since it was incurred;

     - a liability that is traceable under applicable Treasury Regulations to
       capital expenditures with respect to the property; and

     - a liability that was incurred in the ordinary course of the trade or
       business in which property transferred to the partnership was used or
       held, but only if all the assets related to that trade or business are
       transferred, other than assets that are not material to a continuation of
       the trade or business.

     A liability incurred within two years of the transfer is presumed to be
incurred in anticipation of the transfer unless the facts and circumstances
clearly establish that the liability was not incurred in anticipation of the
transfer. However, to the extent that a contributing partner incurs a
refinancing liability
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<PAGE>   96

and the proceeds thereof are allocable under the Treasury Regulations to
payments discharging all or part of any other liability of that partner or of
the partnership, the refinancing debt is considered the same as the other
liability for purposes of the disguised sale regulations. Finally, if a partner
treats a liability incurred within two years of the transfer as a qualified
liability because the facts clearly establish that it was not incurred in
anticipation of the transfer, such treatment must be disclosed to the Internal
Revenue Service in the manner set forth in the disguised sale regulations.

     Cornerstone and Cornerstone Partnership believe that all liabilities of
Cornerstone Partnership that will be assumed in the partnership merger by EOP
Partnership, or to which the assets of Cornerstone Partnership are subject, are
qualified liabilities and thus will not result in recognition of gain to the
Cornerstone Partnership unitholders under the disguised sale rules. There can be
no assurance, however, that the Internal Revenue Service will not contend
otherwise.

     Cash distributions from a partnership to a partner also may be treated as a
transfer of property for purposes of the disguised sale rules. However, a cash
distribution will not be treated as part of a disguised sale if it is
attributable to a "reasonable preferred return" or is a distribution of
"operating cash flow." EOP Partnership anticipates that any ongoing cash
distributions that it make to its unitholders, including the former Cornerstone
Partnership unitholders, will qualify as distributions of operating cash flow
and, thus, will not be considered part of a disguised sale. EOP Partnership
cannot guarantee, however, that circumstances will not change and that EOP
Partnership will not make one or more extraordinary cash distributions that
could be viewed as part of a disguised sale to the extent received by former
Cornerstone Partnership unitholders.

     EOP Partnership unitholders have "unit redemption rights," which entitle
the unitholders to require EOP Partnership to pay the unitholder the fair market
value of the EOP partnership unit in cash, unless Equity Office elects to
acquire the unit for cash or an Equity Office common share. The existence of the
unit redemption rights with respect to the EOP Partnership units issued in the
partnership merger should not be considered to be additional consideration for
purposes of the disguised sale rules. However, if a Cornerstone Partnership
unitholder that acquires EOP Partnership units in the partnership merger were to
exercise the unit redemption right at the time of or shortly after the
partnership merger, there may be a risk that the payment of cash by EOP
Partnership would result in disguised sale treatment of the partnership merger
for that unitholder. EOP Partnership intends to take the position that an
exercise of a unit redemption right by a former Cornerstone Partnership
unitholder following the partnership merger does not result in disguised sale
treatment for the partnership merger. EOP Partnership cannot guarantee, however,
that the Internal Revenue Service would not successfully challenge this
position. Furthermore, if the Internal Revenue Service did challenge this
position, EOP Partnership cannot guarantee that the adverse tax effects would be
limited to the unitholder that exercised its unit redemption right, although, as
noted previously, recently proposed Treasury Regulations, if adopted, should
limit disguised sale treatment only to the former Cornerstone Partnership
unitholder that exercised its unit redemption right.

     If a disguised sale to EOP Partnership of all or a portion of the assets of
Cornerstone Partnership or a Cornerstone Partnership unitholder's units to EOP
Partnership is deemed to occur, a unitholder could be required to recognize some
or all of the deferred gain represented by the excess of the fair market value
of its Cornerstone Partnership units over the unitholder's basis in those units.
The disguised sale would be treated as a sale for all purposes of the Internal
Revenue Code and would be considered to take place on the date that, under
general principles of federal tax law, EOP Partnership becomes the owner of the
property. If the transfer of money or other consideration from EOP Partnership
occurs after the partnership merger, EOP Partnership would be treated as having
acquired the property at the time of the partnership merger and having issued an
obligation to transfer to Cornerstone Partnership or the unitholders, as
applicable, money or other consideration at a later date.

     Moreover, if a transfer of property to a partnership is treated as part of
a disguised sale without regard to the partnership's assumption of or taking
subject to a qualified liability, then the partnership's assumption of or taking
subject to that liability is treated as a transfer of additional consideration
to the transferring partner. The amount of a qualified liability that will be
treated as additional consideration is

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generally an amount determined by multiplying the amount of the qualified
liability by the partner's "net equity percentage." The net equity percentage is
generally the amount of consideration received by the partner, other than relief
from qualified liabilities, divided by the partner's net equity in the property
sold, as calculated under the disguised sale regulations.

     Distribution of Marketable Securities. The partnership merger will be
treated as a contribution of assets by Cornerstone Partnership to EOP
Partnership in exchange for EOP Partnership units, followed by a distribution of
those EOP Partnership units to the Cornerstone Partnership unitholders in
liquidation of Cornerstone Partnership. Under section 731 of the Internal
Revenue Code, a Cornerstone Partnership unitholder could recognize gain or loss
on the distribution by Cornerstone Partnership of EOP Partnership units if the
EOP Partnership units are considered "marketable securities" unless specified
conditions are met. Marketable securities, for these purposes, include actively
traded securities, such as publicly traded REIT shares, or equity interests in
another entity that are readily convertible into or exchangeable for money or
marketable securities. EOP Partnership unitholders have the right to redeem
their units for Equity Office common shares, which are marketable securities, or
cash based upon the value of Equity Office common shares, at the election of
Equity Office. Accordingly, EOP Partnership units could be considered to be
readily exchangeable for money or marketable securities.

     However, Treasury Regulations under section 731(c) provide that a
distribution of marketable securities will not be taxable under that section if
specified conditions are met. As applied to the partnership merger, those
conditions would be met if:

     - the EOP Partnership units are acquired by Cornerstone Partnership in the
       partnership merger and the partnership merger qualifies as a
       nonrecognition transaction for EOP Partnership and Cornerstone
       Partnership;

     - the value at the time of the partnership merger of any securities and
       money of Cornerstone Partnership that are contributed to EOP Partnership
       in the partnership merger is less than 20% of the value of all the assets
       contributed by Cornerstone Partnership to EOP Partnership in the
       partnership merger; and

     - Cornerstone Partnership distributes the EOP Partnership units to its
       unitholders within five years after the partnership merger.

     EOP Partnership and Cornerstone Partnership believe that the distribution
of EOP Partnership units in the partnership merger would not be treated as a
taxable distribution of marketable securities under section 731(c) because these
conditions described in the Treasury Regulations would be satisfied.

     Section 465(e) Recapture. Under section 465 of the Internal Revenue Code, a
taxpayer's ability to use losses to offset taxable income is limited by rules
that are referred to as the "at-risk" rules. See "-- Tax Consequences of
Ownership of EOP Partnership Units After the Partnership Merger -- Limitations
on Deductibility of Losses; Treatment of Passive Activities and Portfolio
Income" below. In addition, the at-risk rules may require a taxpayer to
"recapture" losses that were previously used by the taxpayer with respect to an
"activity" if the taxpayer's "at-risk amount" for the activity falls below zero
at the close of the taxable year. Losses are recaptured by including the amount
of the losses previously used by the taxpayer in the taxpayer's taxable income
for the year of the recapture.

     The identification and scope of an activity and the calculation of the
at-risk amount under the at-risk rules are highly complex and can involve
uncertainties. Generally, a taxpayer's at-risk amount for an activity is the
amount of the taxpayer's investment in the activity, which is increased by the
taxpayer's income from the activity and the taxpayer's share of the "qualified
nonrecourse financing," as defined in section 465(b)(6) of the Internal Revenue
Code, with respect to the activity, and reduced by the taxpayer's losses and
distributions from the activity. It is possible that the partnership merger
and/or the repayment or refinancing of some outstanding indebtedness of
Cornerstone Partnership that constitutes qualified nonrecourse financing at the
time of or following the partnership merger could cause a Cornerstone
Partnership unitholder's at-risk amount to be reduced below zero, which could,
in turn, cause

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the Cornerstone Partnership unitholder to recognize taxable income as a result
of the section 465(e) recapture provisions. The definition of qualified
nonrecourse financing is different from, and sometimes more restrictive than,
the definition of nonrecourse liabilities for purposes of determining basis,
discussed above. For example, debt issued by EOP Partnership in the public debt
markets may not qualify as qualified nonrecourse financing even if it qualifies
as a nonrecourse liability. It is therefore possible that a unitholder could
incur a reduction in its share of qualified nonrecourse financing that causes it
to recognize taxable income under the section 465(e) recapture rules even if the
unitholder does not have a reduction in its nonrecourse liabilities that causes
it to recognize gain as the result of a deemed cash distribution, as described
above.

EFFECT OF SUBSEQUENT EVENTS

     Even if a Cornerstone Partnership unitholder is not required to recognize
gain at the time of the partnership merger, subsequent events could cause a
Cornerstone Partnership unitholder who becomes an EOP Partnership unitholder in
the partnership merger to recognize part or all of the unitholder's gain that is
not recognized at the time of the partnership merger. Subsequent events that
could cause the recognition of gain to a former Cornerstone Partnership
unitholder include:

     - the sale of individual properties by EOP Partnership, particularly those
       acquired from Cornerstone Partnership and with respect to which the
       former Cornerstone Partnership unitholder had substantial deferred gain
       even before the partnership merger;

     - a distribution by EOP Partnership to one or more EOP Partnership
       unitholders of a property formerly held by Cornerstone Partnership with
       respect to which gain would have been recognized for tax purposes, but
       was deferred, either at the time the former Cornerstone Partnership
       unitholder contributed the property to Cornerstone Partnership or at the
       time of the partnership merger;

     - the refinancing, repayment or other reduction in the amount of existing
       debt secured by individual properties, particularly those acquired from
       Cornerstone Partnership and with respect to which the former Cornerstone
       Partnership unitholder had substantial deferred gain even before the
       partnership merger;

     - the issuance of additional EOP Partnership units, which could reduce the
       former Cornerstone Partnership unitholder's share of EOP Partnership
       liabilities;

     - an increase in the basis of a property formerly held by Cornerstone
       Partnership, due to capital expenditures or otherwise, with respect to
       which the former Cornerstone Partnership unitholder had substantial
       deferred gain even before the partnership merger; and

     - the elimination of the disparity between the current tax bases of the
       Cornerstone Partnership properties and the "book bases" of the
       properties, which are based on the fair market value of the properties at
       the time of the partnership merger, which has the effect of reducing the
       amount of indebtedness allocable to former Cornerstone Partnership
       unitholders for basis purposes and, therefore, can result in deemed cash
       distributions. See "-- Tax Consequences of Ownership of EOP Partnership
       Units After the Partnership Merger -- Tax Allocations with Respect to
       Book-Tax Difference on Contributed Properties" below.

     Equity Office, as the general partner of EOP Partnership, is not required
to take into account the tax consequences to the remaining EOP Partnership
unitholders, including the former Cornerstone Partnership unitholders, in
deciding whether EOP Partnership will undertake specific transactions, and the
EOP Partnership unitholders generally do not have the right to approve or
disapprove specific transactions. However, under the merger agreement, Equity
Office and EOP Partnership have agreed not to undertake specific transactions
involving several specific properties that will be acquired from Cornerstone
Partnership in the partnership merger unless EOP Partnership either:

     - obtains the prior written consent of specified former Cornerstone
       Partnership unitholders; or

     - compensates those specified former Cornerstone Partnership unitholders
       for the acceleration of any tax liability incurred by them due to the
       transaction, with any compensation to be paid to a former

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       Cornerstone Partnership unitholder under these circumstances to be
       determined under the existing agreement between Cornerstone Partnership
       and the unitholder.

See "The Merger Agreement -- Tax Related Undertakings of EOP Partnership -- Debt
Maintenance and Lock-up Agreements." Except for these specific commitments, EOP
Partnership and Equity Office have not made any commitment to Cornerstone,
Cornerstone Partnership or any of the Cornerstone Partnership unitholders not to
undertake transactions that will cause the former Cornerstone Partnership
unitholders to recognize all or part of the taxable gain that was deferred
either through the original contribution of assets to Cornerstone Partnership
for Cornerstone Partnership units or through the partnership merger.

     Sale of Individual Properties. If EOP Partnership sells assets acquired
from Cornerstone Partnership in the partnership merger that have significant
unrealized gain under applicable Treasury Regulations, the former Cornerstone
Partnership unitholders would be specially allocated an amount of taxable gain
equal to the unrealized gain, reduced by any amortized amounts. Those former
Cornerstone Partnership unitholders would report the additional gain on their
individual federal income tax returns, but would not be entitled to any special
distributions from EOP Partnership in connection with a sale of former
Cornerstone Partnership assets by EOP Partnership. Thus, the former Cornerstone
Partnership unitholders may not receive cash distributions from EOP Partnership
sufficient to pay their additional taxes if former Cornerstone Partnership
properties are sold. A former Cornerstone Partnership unitholder, however, may
be able to use any passive losses or passive loss carryforwards to offset any
unrealized gain that it must recognize, subject to any applicable passive loss
limitations, including special limitations that would apply if EOP Partnership
were to be classified as a publicly traded partnership. See "-- Tax Status of
EOP Partnership."

     The treatment of the unrealized gain in the absence of a sale of any former
Cornerstone Partnership assets will depend on the method that EOP Partnership
uses to deal with unrealized gain. For a discussion of the impact to the EOP
Partnership unitholders of unrealized gain in the absence of a sale of a
property, see "-- Tax Consequences of Ownership of EOP Partnership Units After
the Partnership Merger -- Tax Allocations with Respect to Book-Tax Difference on
Contributed Properties" below.

     Distributions of Property. Upon the distribution by a partnership of
property to another partner within seven years of when the property was
contributed to the partnership, section 704(c)(1)(B) of the Internal Revenue
Code generally requires that the partner who contributed that property to the
partnership recognize any gain that existed, but was deferred, for federal
income tax purposes with respect to the property at time of the contribution.
Similarly, section 737 of the Internal Revenue Code generally requires the
recognition of a contributing partner's deferred gain upon the distribution by a
partnership to that partner of other partnership property within seven years of
when that partner contributed appreciated property to the partnership.
Accordingly, a former Cornerstone Partnership unitholder who contributed
appreciated property to Cornerstone Partnership could recognize gain under
either of these provisions if EOP Partnership either distributes a property
formerly held by Cornerstone Partnership to one or more other EOP Partnership
unitholders or distributes any EOP Partnership property to that Cornerstone
Partnership unitholder within seven years of when the contributing Cornerstone
Partnership unitholder originally contributed the property to Cornerstone
Partnership. However, under specific exceptions in the applicable Treasury
Regulations, neither of these provisions will apply to cause the recognition of
gain by a Cornerstone Partnership unitholder at the time of the partnership
merger. Similarly, gain that is deferred at the time of the partnership merger
with respect to appreciated assets of Cornerstone Partnership that are
contributed to EOP Partnership, to the extent allocable to a former Cornerstone
Partnership unitholder, will be subject to gain recognition under these
provisions upon a distribution of property by EOP Partnership within seven years
after the partnership merger.

     Refinancing of the Indebtedness Secured by Individual Properties. As
described above under "-- Tax Consequences of the Partnership Merger to
Cornerstone Partnership Unitholders That Receive EOP Partnership
Units -- Reduction in Share of Partnership Liabilities/Deemed Cash Distribution"
a Cornerstone Partnership unitholder could recognize taxable gain as a result of
a reduction in the unitholder's share of partnership liabilities either in
connection with the partnership merger or due to later events. EOP Partnership
cannot guarantee that a future refinancing of the indebtedness securing a
property

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<PAGE>   100

would not result in a reduction of the liabilities allocated to the former
Cornerstone Partnership unitholders, causing the former Cornerstone Partnership
unitholders to recognize taxable gain. EOP Partnership's current long-term
financing strategy is to have as little debt as possible that is secured by
individual properties and to have as much of its debt as possible in the form of
unsecured debt, held either by the public or by institutional investors. This
debt may or may not be recourse to Equity Office, as the general partner of EOP
Partnership. In addition, this debt may not qualify as either a nonrecourse
liability for purposes of determining a unitholder's share of partnership
liabilities or as qualified nonrecourse financing under the at-risk rules. Even
if this unsecured debt qualified as a nonrecourse liability, the amount of
section 704(c) minimum gain with respect to properties that previously secured
traditional mortgage indebtedness would likely be reduced significantly, which
would result in a reduction of nonrecourse liabilities allocable to former
Cornerstone Partnership unitholders and thus a deemed cash distribution.
Generally, the maximum amount of gain that any former Cornerstone Partnership
unitholder could recognize as a result of a reduction in liabilities is the
amount by which its share of the indebtedness of Cornerstone Partnership exceeds
its share of the tax basis of the Cornerstone Partnership assets, which amount
is commonly referred to as a "negative tax capital account."

TAX CONSEQUENCES OF OWNERSHIP OF EOP PARTNERSHIP UNITS AFTER THE PARTNERSHIP
MERGER

     Income and Deductions in General. Each EOP Partnership unitholder will be
required to report on its income tax return its allocable share of income,
gains, losses, deductions and credits of EOP Partnership. Each EOP Partnership
unitholder will be required to include these items on its federal income tax
return even if the unitholder has not received any cash distributions from EOP
Partnership. For each taxable year, EOP Partnership is required to furnish to
each EOP Partnership unitholder a Schedule K-1 that sets forth the unitholder's
allocable share of any income, gains, losses, deductions and credits of EOP
Partnership. EOP Partnership is not required to pay any federal income tax
directly.

     Treatment of EOP Partnership Distributions. Distributions of money by EOP
Partnership to an EOP Partnership unitholder, including deemed distributions
that result from a reduction in the unitholder's share of EOP Partnership
liabilities, generally will result in taxable gain to the unitholder only if and
to the extent that the distribution exceeds the unitholder's basis in its EOP
Partnership units immediately before the distribution. A portion of the gain may
be taxable as ordinary income. Any reduction in an EOP Partnership unitholder's
share of EOP Partnership's nonrecourse liabilities, whether through repayment,
refinancing with recourse liabilities, refinancing with nonrecourse liabilities
secured by the other properties as to which the unitholder does not have section
704(c) minimum gain, or otherwise, will constitute a deemed distribution of
money to the unitholder. In addition, an issuance of additional units by EOP
Partnership without a corresponding increase in EOP Partnership's nonrecourse
liabilities could decrease an EOP Partnership unitholder's share of EOP
Partnership nonrecourse liabilities, resulting in a deemed distribution of money
to an EOP Partnership unitholder.

     A distribution of property other than money by EOP Partnership to its
unitholders ordinarily does not result in the recognition of gain or loss by
either EOP Partnership or the unitholder unless the property is a marketable
security for purposes of section 731(c) of the Internal Revenue Code and the
exceptions to the requirement for recognition of gain do not apply. In that
event, the property would be treated as money and the unitholder would recognize
gain, but not loss, to the extent described above.

     Upon the distribution of property to another partner within seven years of
when the property was contributed to the partnership, section 704(c)(1)(B) of
the Internal Revenue Code generally requires that the partner who contributed
that property to the partnership recognize any gain that existed, but was
deferred, for federal income tax purposes with respect to the property at time
of the contribution. Similarly, section 737 of the Internal Revenue Code
generally requires the recognition of a contributing partner's deferred gain
upon the distribution to that partner of other partnership property within seven
years of when that partner contributed appreciated property to the partnership.
For a discussion of these provisions with respect to the partnership merger and
former Cornerstone Partnership unitholders, see "-- Effect of Subsequent
Events -- Distributions of Property" above.

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<PAGE>   101

     Initial Basis of Units. In general, a Cornerstone Partnership unitholder
who acquires EOP Partnership units in the partnership merger will have an
initial basis in its EOP Partnership units equal to its basis in its Cornerstone
Partnership units, adjusted to reflect the effects of the partnership merger.

     An EOP Partnership unitholder's initial basis in its EOP Partnership units
will generally be increased by the unitholder's share of:

     - EOP Partnership taxable income;

     - any increases in nonrecourse liabilities incurred by EOP Partnership; and

     - recourse liabilities to the extent the EOP Partnership unitholder elects
       to take on a deficit restoration obligation.

     Generally, an EOP Partnership unitholder's initial basis in its units will
be decreased, but not below zero, by the unitholder's share of:

     - EOP Partnership distributions;

     - decreases in liabilities of EOP Partnership, including any decrease in
       its share of the nonrecourse liabilities of the EOP Partnership;

     - losses of EOP Partnership; and

     - nondeductible expenditures of EOP Partnership that are not chargeable to
       capital.

     Allocations of EOP Partnership Income, Gain, Loss and Deductions. The
partnership agreement of EOP Partnership generally provides that net losses will
be allocated among the unitholders in proportion to their respective percentage
ownership interests in EOP Partnership. However, a holder of EOP Partnership
class A units will not be allocated net losses that would have the effect of
creating a deficit balance in its capital account, as specially adjusted for
such purpose, which losses are referred to as excess losses. Excess losses will
be allocated first to Equity Office in an amount equal to the excess of the
aggregate recourse debt of EOP Partnership over the aggregate deficit
restoration obligations of the EOP Partnership unitholders; second, to EOP
Partnership unitholders who have deficit restoration obligations in proportion
to and to the extent of their respective deficit restoration obligations; and
thereafter, to Equity Office.

     The partnership agreement of EOP Partnership generally provides that net
income first will be allocated proportionately to unitholders who have deficit
restoration obligations in one amount equal to the cumulative net losses
allocated to such unitholders. Second, Equity Office will be allocated net
income equal to the cumulative net losses allocated to Equity Office that
represented the excess of the aggregate recourse debt of EOP Partnership over
the aggregate deficit restoration obligations of EOP Partnership unitholders.
Third, net income will be allocated to any preferred unitholders to the extent
necessary to reflect and preserve the economic rights associated with the
particular preferred units. Finally, any remaining net income shall be allocated
in proportion to the respective percentage ownership interests of the
unitholders.

     In connection with the partnership merger, the partnership agreement of EOP
Partnership will be amended to apply the special allocations of loss with
respect to unitholders who have deficit restoration obligations to former
Cornerstone Partnership unitholders who enter into deficit restoration
obligations with EOP Partnership as permitted under the merger agreement. For a
more detailed discussion of the opportunity of Cornerstone Partnership
unitholders to enter into deficit restoration obligations, see "The Merger
Agreement -- Tax Related Undertakings of EOP Partnership -- Deficit Restoration
Obligations" above.

     Under Section 704(b) of the Code, a partnership's allocation of any item of
income, gain, loss or deduction to a partner will be given effect for federal
income tax purposes so long as it has "substantial economic effect," or is
otherwise in accordance with the "partner's interest in the partnership." If an
allocation of an item does not satisfy this standard, it will be reallocated
among the partners on the basis of their respective interests in the
partnership, taking into account all facts and circumstances. EOP

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<PAGE>   102

Partnership believes that the allocations of items of income, gain, loss and
deduction under the partnership agreement, as described above, will be
considered to have substantial economic effect under the applicable Treasury
Regulations.

     Tax Allocations with Respect to Book-Tax Difference on Contributed
Properties. Under section 704(c) of the Internal Revenue Code, income, gain,
loss and deduction attributable to appreciated or depreciated property that is
contributed to a partnership must be allocated for federal income tax purposes
in a manner such that the contributor is charged with, or benefits from, the
unrealized gain or unrealized loss associated with the property at the time of
contribution. The amount of unrealized gain or unrealized loss is generally
equal to the difference between the fair market value of the contributed
property at the time of contribution and the adjusted tax basis of the property
at the time of contribution, which is referred to as the "book-tax difference."
A book-tax difference also can exist with respect to an asset that has not
appreciated or depreciated in economic terms if that asset has been depreciated
for tax purposes. At the time of the partnership merger, a substantial book-tax
difference is likely to exist with respect to the assets acquired from
Cornerstone Partnership, particularly those that Cornerstone Partnership
previously acquired in exchange for its units.

     The partnership agreement of EOP Partnership requires allocations of
income, gain, loss and deduction attributable to the Properties be made in a
manner that is consistent with section 704(c) of the Internal Revenue Code.
Treasury Regulations under section 704(c) require partnerships to use a
"reasonable method" for allocation of items affected by section 704(c) of the
Internal Revenue Code. EOP Partnership uses the "traditional method," one of the
three methods outlined by the Treasury Regulations under section 704(c), for its
existing properties, and is required to use such method for the properties it
acquires from Cornerstone Partnership. Under the traditional method, former
Cornerstone Partnership unitholders will be allocated less depreciation and,
therefore, more income with respect to the assets owned by Cornerstone
Partnership prior the partnership merger. The effects of these allocations will
be different for different Cornerstone Partnership unitholders and will depend
upon which, if any, properties those unitholders originally contributed to
Cornerstone Partnership and the amount of depreciation, if any, that remains to
be claimed with respect to those properties. These reduced allocations of
depreciation and increased allocations of income will be offset at least in part
by increased allocations of depreciation and reduced allocations of income with
respect to properties owned by EOP Partnership before the partnership merger.

     If an asset that was acquired from Cornerstone Partnership is sold by EOP
Partnership, gain equal to any book-tax difference remaining at the time of such
sale must be allocated exclusively to the former Cornerstone Partnership
unitholders, even though the proceeds of the sale will be allocated
proportionately among all EOP Partnership unitholders. Conversely, no gain
attributable to any book-tax difference remaining in an existing EOP Partnership
property at the time of a sale will be allocated to the former Cornerstone
Partnership unitholders. Under the traditional method, however, the gain
required to be specially allocated would not exceed the gain that is recognized
by EOP Partnership on the sale. The amount of gain allocated to specific former
Cornerstone Partnership unitholders with respect to former Cornerstone
Partnership assets would depend upon a number of variables, including the
book-tax difference that existed with respect to such assets within Cornerstone
Partnership before the partnership merger; whether the former Cornerstone
Partnership unitholder owns units issued in exchange for the contribution of
that asset to Cornerstone Partnership; the amount of the additional book-tax
difference that was created as a result of the partnership merger with respect
to the asset; and the amount of the book-tax difference with respect to that
asset that has been amortized since the partnership merger and before the sale
of the asset through the special allocations of depreciation deductions
described above.

     The partnership agreement of EOP Partnership also requires that any gain
allocated to the EOP Partnership unitholders upon the sale or other taxable
disposition of any EOP Partnership asset must, to the extent possible after
taking into account other required allocations of gain, be characterized as
recapture income in the same proportions and to the same extent as the
unitholders previously have been allocated any deductions directly or indirectly
giving rise to the treatment of the gains as recapture income.

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<PAGE>   103

     Liquidation of EOP Partnership. If EOP Partnership liquidates and
dissolves, a distribution of EOP Partnership property other than money generally
will not result in taxable gain to an EOP Partnership unitholder, except to the
extent provided in sections 737, 704(c)(1)(B) and 731(c) of the Internal Revenue
Code. The basis of any distributed property to an EOP Partnership unitholder
will equal the adjusted basis of the unitholder's EOP Partnership units, reduced
by any money distributed in liquidation. A distribution of money upon the
liquidation of EOP Partnership, however, will be taxable to an EOP Partnership
unitholder to the extent that the amount of money distributed in liquidation,
including any deemed distributions of cash as a result of a reduction in the
unitholder's share of partnership liabilities, exceeds the unitholder's tax
basis in its EOP Partnership units. If Equity Office issued its shares of
beneficial interest to EOP Partnership unitholders upon the liquidation of EOP
Partnership, it is likely that each EOP Partnership unitholder would be treated
as if it had exchanged its EOP Partnership units for Equity Office shares and
the unitholder would recognize gain or loss as if its EOP Partnership units were
sold in a fully taxable exchange. See "-- Redemptions of EOP Partnership Units"
below.

     Limitations on Deductibility of Losses; Treatment of Passive Activities and
Portfolio Income. Generally, individuals, estates, trusts and some closely held
corporations and personal service corporations can deduct losses from "passive
activities" only to the extent that those losses do not exceed the taxpayer's
income from passive activities. Generally, passive activities are activities or
investments in which the taxpayer does not materially participate, which would
include the ownership of interests in EOP Partnership. If EOP Partnership were
classified as a publicly traded partnership under the Internal Revenue Code, any
losses or deductions allocable to an EOP Partnership unitholder could be used
only against gains or income of EOP Partnership and could not be used to offset
passive income from other passive activities. Similarly, any EOP Partnership
income or gain allocable to an EOP Partnership unitholder could not be offset
with losses from other passive activities of the unitholder. For a more detailed
discussion of EOP Partnership's possible classification as a publicly traded
partnership, see "-- Tax Status of EOP Partnership" above.

     In addition, an EOP Partnership unitholder may not deduct its share of any
EOP Partnership losses to the extent that those losses exceed the lesser of:

     - the adjusted tax basis of its EOP Partnership units at the end of EOP
       Partnership's taxable year in which the loss occurs; and

     - the amount for which such unitholder is considered "at-risk" at the end
       of that year.

     In general, an EOP Partnership unitholder will be at-risk to the extent of
its basis in its EOP Partnership units, except to the extent that the unitholder
acquired its units using nonrecourse debt. For these purposes, a unitholder's
basis in its EOP Partnership units will include only the unitholder's share of
EOP Partnership's liabilities, as determined under section 752 of the Internal
Revenue Code, that are considered "qualified nonrecourse financing" for purposes
of these at-risk rules. EOP Partnership believes that all of the debt secured by
its properties that otherwise qualifies as nonrecourse liabilities under section
752 of the Internal Revenue Code will constitute qualified nonrecourse financing
for purposes of the at-risk rules, but EOP Partnership cannot guarantee that the
Internal Revenue Service might not successfully contend that some or all of the
debt secured by EOP Partnership's properties is not qualified nonrecourse
financing. In addition, there can be no assurance that EOP Partnership will not
repay some or all of its qualified nonrecourse financing in the future with
proceeds from equity offerings or proceeds of debt that do not constitute
qualified nonrecourse financing.

     After the partnership merger, a former Cornerstone Partnership unitholder's
at-risk amount generally will increase or decrease as the adjusted basis in its
EOP Partnership units increases or decreases, except for increases or decreases
attributable to EOP Partnership liabilities that do not constitute qualified
nonrecourse financing. If an EOP Partnership unitholder is not allowed to use
losses in a particular taxable year because of the application of the at-risk
rules, the losses can be carried forward and may be used by the unitholder to
offset income in a subsequent year to the extent that the unitholder's adjusted
basis or

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at-risk amount, whichever was the limiting factor, is increased in that
subsequent year. The at-risk rules apply to:

     - an individual unitholder;

     - an individual shareholder or partner of a unitholder that is an S
       corporation or partnership; and

     - a unitholder that is a corporation if 50% or more of the value of that
       corporation's stock is owned, directly or indirectly, by five or fewer
       individuals at any time during the last half of the taxable year.

     Disposition of EOP Partnership Units. If an EOP Partnership unit is sold,
transferred as a gift, or otherwise disposed of, gain or loss from the
disposition will be based on the difference between the amount realized on the
disposition and the basis attributable to the EOP Partnership unit. The amount
realized on the disposition of a unit generally will equal the sum of:

     - any cash received;

     - the fair market value of any other property received; and

     - the amount of EOP Partnership liabilities allocated to the unit.

     Accordingly, a unitholder will recognize gain on the disposition of a unit
to the extent that the amount realized exceeds the unitholder's basis for the
EOP Partnership unit. Because the amount realized includes any amount
attributable to the relief from EOP Partnership liabilities attributable to the
unit, a unitholder could have taxable income, or perhaps even a tax liability,
in excess of the amount of cash and property received upon the disposition the
unit.

     Generally, gain recognized on the disposition of an EOP Partnership unit
will be capital gain. However, any portion of the EOP unitholder's amount
realized on the disposition of a unit that is attributable to "unrealized
receivables" of EOP Partnership, as defined in section 751 of the Internal
Revenue Code, will give rise to ordinary income. The amount of ordinary income
that would have to be recognized would be equal to the amount by which the
unitholder's share of unrealized receivables of EOP Partnership exceeds the
unitholder's basis attributable to those assets. Unrealized receivables include,
to the extent not previously included in EOP Partnership's income, any rights to
payment for services rendered or to be rendered. Unrealized receivables also
include amounts attributable to prior depreciation deductions that would be
subject to recapture as ordinary income if EOP Partnership had sold its assets
at their fair market value at the time of the redemption.

     For individuals, trusts and estates, net capital gain from the sale of an
asset held one year or less is subject to tax at the applicable rate for
ordinary income. For these taxpayers, the maximum rate of tax on the net capital
gain from a sale or exchange of an asset held for more than one year generally
is 20%. However, a 25% rate applies to the extent that net capital gains
attributable to the sale of depreciable real property are attributable to prior
depreciation deductions not otherwise recaptured as ordinary income under other
depreciation recapture rules. The applicable provisions of the Internal Revenue
Code give the Internal Revenue Service the authority to publish Treasury
Regulations regarding the application of the 25% rate to a sale of an interest
in a pass-through entity, such as a partnership, to the extent that the gain
realized on the sale of the interest is attributable to prior depreciation
deductions by the partnership that have not otherwise been recaptured as
ordinary income. The Internal Revenue Service has issued proposed regulations
regarding the application of the 25% rate to sales of interests in partnerships.
While there is some uncertainty regarding whether the 25% rate would apply to
sales of partnership interests before final Treasury Regulations are issued, the
IRS has taken the position, for which there appears to be some support in the
applicable legislative history, that the 25% rate currently applies to sales of
interests in partnerships. Under this view, any gain on the sale of an EOP
Partnership unit held for more than one year could be treated partly as gain
from the sale of a long-term capital asset subject to a 20% tax rate, partly as
gain from the sale of depreciable real property subject to a 25% tax rate to the
extent attributable to prior depreciation deductions by EOP Partnership that
have not been otherwise recaptured as ordinary income, and partly as ordinary
income to the extent attributable to unrealized receivables. Even in the
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event that the 25% exception does not currently apply to sales of interests in
partnerships that hold depreciable real property, the IRS has proposed
regulations that, if finalized, would apply the exception definitively to such a
sale. Each EOP Partnership unitholder should consult with its own tax advisor
regarding the application of the 25% rate to a sale of EOP Partnership units and
the potential application of the proposed Treasury Regulations.

     Redemptions of EOP Partnership Units. If an EOP Partnership unitholder
exercises his unit redemption right, it is likely that Equity Office will elect
to exercise its right under the EOP Partnership Agreement to acquire the
unitholder's EOP Partnership units in exchange for cash or Equity Office common
shares. However, Equity Office is under no obligation to exercise this right. If
Equity Office does elect to acquire a unitholder's EOP Partnership units in
exchange for cash or Equity Office common shares, the transaction will be a
fully taxable sale to the unitholder. The amount realized by a unitholder on
this kind of disposition of an EOP Partnership unit will equal the sum of:

     - any cash received;

     - the fair market value of any Equity Office common shares received; and

     - the amount of EOP Partnership liabilities allocated to the unit
       exchanged.

The unitholder's taxable gain and the tax consequences of that gain would be
determined as described under "-- Disposition of EOP Partnership Units" above.

     If Equity Office does not elect to acquire the EOP Partnership unitholder's
units in exchange for cash or Equity Office common shares, EOP Partnership is
required to redeem those EOP Partnership units for cash. If the EOP Partnership
redeems EOP Partnership units for cash contributed by Equity Office in order to
effect the redemption, the redemption likely will be treated as a sale of the
EOP Partnership units to Equity Office in a fully taxable transaction, although
the matter is not free from doubt. Under these circumstances, the redeeming
unitholder's amount realized will equal the sum of:

     - the cash received; and

     - the amount of EOP Partnership liabilities allocated to the unit redeemed.

The unitholder's taxable gain and the tax consequences of that gain would be
determined as described under "-- Disposition of EOP Partnership Units" above.

     If an EOP Partnership unit is redeemed for cash that is not contributed by
Equity Office to effect the redemption, the unitholder's tax treatment will
depend upon whether or not the redemption results in a disposition of all of the
unitholder's EOP Partnership units. If all of the unitholder's EOP Partnership
units are redeemed, the unitholder's taxable gain and the tax consequences of
that gain will be determined as described under "-- Disposition of EOP
Partnership Units" above. However, if less than all of a unitholder's EOP
Partnership units are redeemed, the unitholder will not be allowed to recognize
loss on the redemption and will recognize taxable gain only if and to the extent
that the unitholder's amount realized on the redemption, calculated as described
above, exceeds the unitholder's basis in all of its EOP Partnership units
immediately before the redemption.

     Partnership Audit Procedures. The federal income tax information returns
filed by EOP Partnership may be audited by the Internal Revenue Service. The
Internal Revenue Code contains partnership audit procedures governing the manner
in which Internal Revenue Service audit adjustments of partnership items are
resolved. Unless and until EOP Partnership elects to be treated as an "electing
large partnership," it is and will continue to be subject to audit rules under
the Tax Equity and Fiscal Responsibility Act of 1982, which is referred to as
TEFRA. See "-- Possible Future Election by EOP Partnership to be Treated as an
Electing Large Partnership" below.

     Partnerships generally are treated as separate entities for purposes of
federal tax audits, judicial review of adjustments by the Internal Revenue
Service, and tax settlement proceedings. The tax treatment of partnership items
of income, gain, loss, deduction and credit is determined at the partnership
level in a unified partnership proceeding, rather than in separate proceedings
with each partner. The Internal
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Revenue Code provides for one partner to be designated as the "tax matters
partner" for these purposes. Equity Office is the tax matters partner for EOP
Partnership.

     The tax matters partner is authorized, but not required, to take some
actions on behalf of EOP Partnership and the unitholders and can extend the
statute of limitations for assessment of tax deficiencies against the EOP
Partnership unitholders with respect to EOP Partnership items. The tax matters
partner will make a reasonable effort to keep each unitholder informed of
administrative and judicial tax proceedings with respect to EOP Partnership
items in accordance with Treasury Regulations issued under section 6223 of the
Internal Revenue Code. In connection with adjustments to EOP Partnership tax
returns proposed by the Internal Revenue Service, the tax matters partner may
bind any unitholder with less than a 1% profits interest in EOP Partnership to a
settlement with the Internal Revenue Service unless the unitholder elects not to
give that authority to the tax matters partner by filing a statement to that
effect with the Internal Revenue Service. The tax matters partner may seek
judicial review, to which all unitholders will be bound, of a final EOP
Partnership administrative adjustment. If the tax matters partner fails to seek
judicial review, it may be sought by any unitholder having at least a 1%
interest in the profits of the EOP Partnership and by unitholders having, in the
aggregate, at least a 5% profits interest. Only one judicial proceeding will go
forward, however, and each unitholder with an interest in the outcome may
participate.

     Unitholders will generally be required to treat EOP Partnership items on
their federal income tax returns in a manner consistent with the treatment of
the items on the EOP Partnership information return. In general, that
consistency requirement is waived if a unitholder files a statement with the
Internal Revenue Service identifying the inconsistency. Failure to satisfy the
consistency requirement, if not waived, will result in an adjustment to conform
the treatment of the item by the unitholder to the treatment on the EOP
Partnership return. Even if the consistency requirement is waived, adjustments
to the unitholder's tax liability with respect to EOP Partnership items may
result from an audit of EOP Partnership's or the unitholder's tax return.
Intentional or negligent disregard of the consistency requirement may subject a
unitholder to substantial penalties. In addition, an audit of the EOP
Partnership return may also lead to an audit of an individual unitholder's tax
return, which could result in adjustment of non-partnership items.

     Possible Future Election by EOP Partnership to be Treated as an Electing
Large Partnership. EOP Partnership has not yet elected, but could elect in the
future, to be treated as an "electing large partnership" for federal tax
purposes. This election is available to partnerships, such as EOP Partnership,
that have 100 or more partners and meet other requirements set forth in the
Internal Revenue Code. The election would entitle EOP Partnership to use a
simplified flow-through reporting system and a special audit system. Although
EOP Partnership has not made an election to be treated as an electing large
partnership, EOP Partnership may determine to make this election for future
taxable years.

     As an electing large partnership, EOP Partnership would be eligible to use
a simplified flow-through reporting system, under which the number of tax items
that unitholders are required to account for separately will be significantly
reduced. For example:

     - miscellaneous itemized deductions will not be separately reported to the
       unitholders, but will be allowed to the EOP Partnership to the extent of
       30 percent of such deductions;

     - charitable contributions will be deductible by EOP Partnership instead of
       being reported to the unitholders; and

     - capital gains and losses will be netted at the partnership level and only
       net capital gain or loss will be reported to the unitholders.

For a description of the reporting rules currently applicable to EOP Partnership
and its unitholders, see "-- Income and Deductions in General" above.

     The audit procedures that are applicable to an electing large partnership
differ from the procedures applicable under TEFRA, as described above under "--
Partnership Audit Procedures." An electing large partnership must designate a
representative to act on its behalf for audit purposes. Unlike a tax matters

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partner under TEFRA, the representative of an electing large partnership would
not have to be a unitholder. The IRS may challenge a reporting position taken by
an electing large partnership by conducting a single administrative proceeding
that will be binding upon all partners, just as under the TEFRA audit rules.
However, partners in an electing large partnership have no individual right to
notice of the adjustment proceedings, to participate in the proceedings or to
file petitions for judicial review of a final administrative adjustment to
partnership items. Adjustments to partnership items will flow through to the
partners for the year that the adjustment "takes effect" within the meaning of
section 6242 of the Code. Moreover, a partner in an electing large partnership
must report all partnership items consistently with their treatment on the
partnership return. If an underpayment results from the failure to report an
item consistently with the treatment of that item on the partnership return, the
amount of the underpayment will be assessed immediately to the partner as if the
underpayment were due to a mathematical or clerical error.

     Alternative Minimum Tax on Items of Tax Preference. The Internal Revenue
Code contains alternative minimum tax rules that are applicable to corporate and
noncorporate taxpayers. EOP Partnership will not be subject to the alternative
minimum tax, but EOP Partnership unitholders are required to take into account
on their own tax returns their respective shares of the EOP Partnership's tax
preference items and adjustments in order to compute their alternative minimum
taxable income. Since the impact of this tax depends on each Cornerstone
Partnership unitholder's particular situation, the Cornerstone Partnership
unitholders are urged to consult with their own tax advisors as to the
applicability of the alternative minimum tax following the partnership merger.

     State and Local Taxes. In addition to the federal income tax aspects
described above, a Cornerstone Partnership unitholder should consider the
potential state and local tax consequences of owning EOP Partnership units. Tax
returns may be required and tax liability may be imposed both in the state or
local jurisdictions where a Cornerstone Partnership unitholder resides and in
each state or local jurisdiction in which EOP Partnership has assets or
otherwise does business. Thus, persons holding EOP Partnership units either
directly or through one or more partnerships or limited liability companies may
be subject to state and local taxation in a number of jurisdictions in which the
EOP Partnership directly or indirectly holds real property and would be required
to file periodic tax returns in those jurisdictions. EOP Partnership also may be
required to withhold state income tax from distributions otherwise payable to
the EOP Partnership unitholders. After the partnership merger, EOP Partnership
will own properties in approximately 25 states and the District of Columbia. EOP
Partnership anticipates providing the EOP Partnership unitholders with any
information reasonably necessary to permit them to satisfy state and local
return filing requirements. To the extent that an EOP Partnership unitholder
pays income tax with respect to EOP Partnership income to a state where it is
not resident or EOP Partnership is required to pay such tax on behalf of such
unitholder, the unitholder may be entitled to a deduction or credit against
income tax that it otherwise would owe to its state of residence with respect to
the same income. A Cornerstone Partnership unitholder should consult with its
personal tax advisor regarding the state and local income tax implications of
owning EOP Partnership units, including return filing requirements in the
various states where EOP Partnership currently owns properties and will own
properties after the partnership merger.

TAX CONSEQUENCES OF THE REDEMPTION OF CORNERSTONE
PARTNERSHIP UNITS FOR CORNERSTONE COMMON STOCK

     Under the merger agreement, a Cornerstone Partnership unitholder may choose
to require Cornerstone Partnership to redeem its Cornerstone Partnership units
for Cornerstone common stock immediately before the consummation of the
partnership merger. If a Cornerstone Partnership unitholder so elects, the
unitholder will become a Cornerstone common stockholder and can elect to
receive, in exchange for its shares of Cornerstone common stock, cash and/or
Equity Office common shares in the REIT merger. The election to receive cash in
the REIT merger will be subject to the proration provisions in the merger
agreement. See "The Merger Agreement -- The REIT Merger."

     A Cornerstone Partnership unitholder who elects to have his Cornerstone
Partnership units redeemed for Cornerstone common stock before the partnership
merger may elect to condition that redemption on the ability to receive only
cash in the REIT merger in exchange for the Cornerstone common stock that

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would be received upon the redemption. If a Cornerstone Partnership unitholder
conditions the redemption of its units on the ability to receive only cash in
the subsequent REIT merger but, based on the elections made by other Cornerstone
common stockholders, the unitholder will not be able to receive only cash for
the units to be redeemed, the redemption will not take place as to those
Cornerstone Partnership units. These determinations will be completed prior to
consummation of the partnership merger. The Cornerstone Partnership units not
redeemed will be exchanged for EOP Partnership units in the partnership merger.

     The redemption of Cornerstone Partnership units will be treated as a fully
taxable sale of units by the Cornerstone Partnership unitholder to Cornerstone
at the time of the redemption. The redeeming Cornerstone unitholder will
recognize gain or loss equal to the difference between:

     - the "amount realized" for tax purposes; and

     - the unitholder's adjusted basis in its Cornerstone Partnership units that
       are redeemed.

     The amount realized will be equal to the fair market value of the
Cornerstone common stock received upon redemption, plus the portion of
Cornerstone Partnership's nonrecourse liabilities allocable to the redeemed
Cornerstone Partnership units. Because the deemed discharge of liabilities is
included in the Cornerstone Partnership unitholder's amount realized, it is
possible that the amount of gain recognized, or even the tax liability resulting
from the gain, could exceed the value of the Cornerstone common stock received
in the redemption.

     For a description of the applicable tax rates that would apply to gain
recognized upon the redemption of Cornerstone Partnership units, see "-- Tax
Consequences of Ownership of EOP Partnership Units After the Partnership
Merger -- Disposition of EOP Partnership Units."

     Generally, a Cornerstone Partnership unitholder who received Cornerstone
Partnership units in exchange for a direct or indirect contribution of property
to Cornerstone Partnership had an initial basis in the Cornerstone Partnership
units equal to the unitholder's basis in the contributed property or, if
applicable, equal to the unitholder's basis in its interest in the entity that
contributed the property. A unitholder's initial basis generally was increased
by:

     - the unitholder's share of Cornerstone Partnership's taxable income; and

     - increases in the unitholder's share of Cornerstone Partnership's
       liabilities, including any increase in the unitholder's share of
       nonrecourse liabilities.

     A unitholder's initial basis generally was decreased, but not below zero,
by:

     - the unitholder's share of Cornerstone Partnership's distributions;

     - decreases in the unitholder's share of Cornerstone Partnership
       liabilities, including nonrecourse liabilities;

     - the unitholder's share of losses of Cornerstone Partnership; and

     - the unitholder's share of nondeductible expenditures of Cornerstone
       Partnership that are not chargeable to capital.

     The specific federal income tax consequences of any redemption of
Cornerstone Partnership units prior to the partnership merger will vary for each
Cornerstone Partnership unitholder according to its own circumstances.
Accordingly, each Cornerstone Partnership unitholder is urged to consult with
its own tax advisor before deciding whether to elect to redeem its Cornerstone
Partnership units for Cornerstone common stock before the partnership merger.

     Potential Application of the Disguised Sale Rules to a Redemption of
Cornerstone Partnership Units. There is a risk that if a Cornerstone Partnership
unit is redeemed, particularly if it is redeemed within two years of when it was
issued, the IRS might contend that the original transaction in which the units
were issued should be treated as a "disguised sale" of property. Under the IRS's
disguised sale rules, unless an exception applies, a partner's contribution of
property to a partnership and a simultaneous or subsequent transfer of money or
other consideration, including the assumption of or taking subject to a
liability, from the partnership to the partner may be treated as a sale, in
whole or in part, of the property by the partner to the partnership. If money or
other consideration is transferred by a partnership to a partner within two

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years of the partner's contribution of property, the transactions are presumed
to be a sale of the contributed property unless the facts and circumstances
clearly establish that the transfers do not constitute a sale. If two years have
passed between the original contribution of property and the subsequent transfer
of money or other consideration, the transactions will not be presumed to be a
sale unless the facts and circumstances clearly establish that the transfers
constitute a sale. For a more detailed discussion of the disguised sale rules,
see "Material Federal Income Tax Consequences of the Partnership Merger to
Cornerstone Partnership Unitholders That Receive EOP Partnership Units --
Disguised Sale" above.

     Basis and Holding Period in Cornerstone Common Stock Received in the
Redemption. A Cornerstone Partnership unitholder who redeems its units for
Cornerstone common stock immediately before the partnership merger will have a
basis in its Cornerstone common stock received in the redemption equal to the
fair market value of the Cornerstone common stock at the time of the redemption.
Because the basis will depend upon the trading value of Cornerstone's common
stock immediately prior to the partnership merger, that basis may not equal the
value of the consideration that the former Cornerstone Partnership unitholder
will receive for such common stock in the REIT merger. The unitholder's holding
period in the Cornerstone common stock received will begin after the redemption.

TAX CONSEQUENCES OF THE REIT MERGER

     The following discussion summarizes the material U.S. federal income tax
consequences relating to the REIT merger and the receipt of cash and/or Equity
Office common shares in the REIT merger by Cornerstone common stockholders. This
discussion is relevant only to a Cornerstone Partnership unitholder who redeems
its Cornerstone Partnership units for Cornerstone common stock before the
partnership merger and only with respect to shares of Cornerstone common stock
received in the redemption. As described above under "Tax Consequences of
Redemption of Cornerstone Partnership Units for Cornerstone Common Stock," a
redeeming Cornerstone Partnership unitholder will be subject to federal income
tax on the redemption. The federal income tax consequences in this section are
in addition to the federal income tax consequences described above with respect
to the redemption. For purposes of this discussion, a redeeming Cornerstone
Partnership unitholder is referred to as a Cornerstone common stockholder.

     Because this is a summary that is intended to address only federal income
tax consequences of the REIT merger that will apply to all Cornerstone
stockholders, it may not contain all the information that may be important to
you.

     YOU ARE URGED BOTH TO REVIEW THE FOLLOWING DISCUSSION AND TO CONSULT WITH
YOUR OWN TAX ADVISOR TO DETERMINE THE EFFECT OF THE REIT MERGER ON YOUR
INDIVIDUAL TAX SITUATION, INCLUDING ANY STATE, LOCAL OR NON-U.S. TAX
CONSEQUENCES.

     The information in this section is based on the current Internal Revenue
Code, current, temporary and proposed regulations, the legislative history of
the Internal Revenue Code, current administrative interpretations and practices
of the Internal Revenue Service, including its practices and policies as
endorsed in private letter rulings, which are not binding on the Internal
Revenue Service, and existing court decisions. Future legislation, regulations,
administrative interpretations and court decisions could change current law or
adversely affect existing interpretations of current law. Any change could apply
retroactively. Neither Equity Office nor Cornerstone has requested, or plans to
request, any rulings from the Internal Revenue Service concerning the tax
treatment of the REIT merger. It is possible that the Internal Revenue Service
would challenge the statements in this discussion, which do not bind the
Internal Revenue Service or the courts, and that a court would agree with the
Internal Revenue Service.

     General. The REIT merger is intended to qualify as a "reorganization" under
section 368(a) of the Internal Revenue Code. The income tax consequences
summarized below are based on the assumption that the REIT merger will qualify
as a reorganization. The obligation of Equity Office and Cornerstone to
consummate the REIT merger is conditioned upon Hogan & Hartson L.L.P., counsel
to Equity Office, and King & Spalding, counsel to Cornerstone, delivering
opinions to Equity Office and Cornerstone, respectively, that the REIT merger
will qualify as a reorganization under the provisions of section 368(a)
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of the Internal Revenue Code. The opinions of counsel will rely on customary
representations made by Equity Office and Cornerstone and applicable factual
assumptions. If any of the factual assumptions or representations relied upon in
the opinions of counsel are inaccurate, the opinions may not accurately describe
the U.S. federal income tax treatment of the REIT merger, and this discussion
may not accurately describe the tax consequences of the REIT merger.

     One particularly important representation that counsel will rely upon in
rendering their opinions will be that the aggregate fair market value of the
Equity Office common shares issued in the REIT merger will represent at least
40% of the aggregate value of the total consideration issued by Equity Office in
the REIT merger, as of the closing of the REIT merger and taking into account
any cash paid for fractional Equity Office common shares. For example, if the
REIT merger had occurred on             , 2000, then based on the trading price
of Equity Office common shares on that date and the number of shares of
Cornerstone common stock issued and outstanding on that date, and assuming that
no Cornerstone Partnership unitholders had converted their units into
Cornerstone common stock immediately before the REIT merger, the aggregate fair
market value of the Equity Office common shares that would have been issued in
the REIT merger would represent approximately      % of the value of the total
consideration paid by Equity Office in the REIT merger. There is no guarantee,
however, that the trading price of the Equity Office common shares will be high
enough at the scheduled closing of the REIT merger to allow counsel to render
the required tax opinions and the REIT merger to be consummated.

     Tax Consequences of the REIT Merger to Cornerstone Common Stockholders. If
the REIT merger of Cornerstone with and into Equity Office constitutes a
reorganization within the meaning of section 368(a) of the Internal Revenue
Code, the REIT merger will have the following material federal income tax
consequences to Cornerstone common stockholders:

     - Equity Office Common Shares Only. The exchange in the REIT merger of
       Cornerstone common stock solely for Equity Office common shares will not
       result in the recognition of gain or loss to a Cornerstone stockholder,
       except with respect to cash received for a fractional Equity Office
       common share, as discussed below.

       A Cornerstone common stockholder that receives only Equity Office common
       shares in the REIT merger will have a tax basis in the Equity Office
       common shares received equal to the stockholder's adjusted tax basis in
       the Cornerstone common stock exchanged.

     - Equity Office Common Shares and Cash. A Cornerstone common stockholder
       that receives both Equity Office common shares and cash, other than cash
       received for a fractional Equity Office common share, will recognize gain
       equal to the lesser of the cash received, or the amount by which (A) the
       cash plus the fair market value of the Equity Office common shares
       received exceeds (B) the stockholder's adjusted tax basis in its
       Cornerstone common stock. A Cornerstone common stockholder that receives
       both Equity Office common shares and cash in the REIT merger will not
       recognize any loss on the exchange.

       In general, gain recognized by a Cornerstone common stockholder that
       receives both cash and Equity Office common shares will be taxable as
       short-term capital gain, assuming that the Cornerstone common stock was
       held as a capital asset. However, it is possible that the gain recognized
       by a Cornerstone common stockholder that receives both cash and Equity
       Office common shares will be taxable as dividend income if the cash
       received does not result in a "meaningful reduction" in the Equity Office
       common shares that the Cornerstone common stockholder would have received
       had it received only Equity Office common shares in the REIT merger. In
       determining whether a meaningful reduction has occurred, section 318 of
       the Internal Revenue Code requires that the stockholder be treated as
       actually owning Equity Office common shares that are owned by the
       stockholder's family members or by entities in which the stockholder owns
       an interest, or which the stockholder has an option to acquire.

       Gain required to be recognized due to the receipt of cash as part of the
       REIT merger consideration generally must be calculated separately for
       each block of Cornerstone common stock exchanged in

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       the REIT merger. A block of stock generally is considered to be a group
       of shares acquired at the same cost in a single transaction.

       A Cornerstone common stockholder that receives both Equity Office common
       shares and cash, other than cash received for a fractional Equity Office
       common share, will have a tax basis in the Equity Office common shares
       received equal to the stockholder's tax basis in its Cornerstone common
       stock exchanged, decreased by the amount of any cash received and
       increased by the amount of gain recognized in the exchange.

     - Cash Only. A Cornerstone stockholder that receives only cash in the REIT
       merger generally will recognize short-term capital gain or loss equal to
       the difference between the amount of cash received and the stockholder's
       adjusted tax basis in its Cornerstone common stock, assuming that the
       Cornerstone common stock was held as a capital asset.

     - Fractional Shares. A Cornerstone common stockholder that receives cash
       instead of a fractional Equity Office common share will be treated as if
       the fractional share was received in the REIT merger and then redeemed by
       Equity Office. The Cornerstone common stockholder generally will
       recognize short-term capital gain or loss equal to the difference between
       the amount of cash received for the fractional share and the
       stockholder's tax basis in the fractional share, assuming that the
       Cornerstone common stock was held as a capital asset.

     - Holding Period. The holding period of the Equity Office common shares
       received by a Cornerstone common stockholder in the REIT merger will
       include the holding period of the Cornerstone common stock exchanged,
       assuming that the Cornerstone common stock was held as a capital asset.

     Backup Withholding. Backup withholding tax at a rate of 31% may apply to
cash paid in the REIT merger to a Cornerstone stockholder. Backup withholding
will not apply, however, if the Cornerstone stockholder:

     - furnishes a correct taxpayer identification number and certifies that he
       or she is not subject to backup withholding on Internal Revenue Service
       Form W-9, or an appropriate substitute form;

     - provides a certificate of foreign status on Internal Revenue Service Form
       W-8 or W-8 BEN, or an appropriate substitute form; or

     - is otherwise exempt from backup withholding.

     The Internal Revenue Service may impose a penalty upon any taxpayer that
fails to provide the correct taxpayer identification number.

     Tax Consequences to Cornerstone and Equity Office. Equity Office will not
recognize any gain as a result of the REIT merger, whether or not the REIT
merger qualifies as a reorganization under section 368(a) of the Internal
Revenue Code.

     Cornerstone will not recognize any gain as a result of the REIT merger if
the REIT merger qualifies as a reorganization under section 368(a) of the
Internal Revenue Code and Cornerstone qualifies as a REIT at the time of the
REIT merger.

     Tax Consequences of the REIT Merger if the REIT Merger Did Not Qualify as a
Reorganization or Cornerstone Did Not Qualify as a REIT. Although it is a
condition to consummation of the REIT merger that Equity Office and Cornerstone
receive opinions of counsel that the REIT merger will qualify as a
reorganization for federal income tax purposes, these opinions will not be
binding upon the Internal Revenue Service or the courts. If the REIT merger did
not qualify as a reorganization for federal income tax purposes, the REIT merger
would be treated as a taxable transaction. Accordingly, Cornerstone would
recognize gain or loss equal to the difference between:

     - the sum of:

      -- the fair market value of the Equity Office common shares issued in the
         REIT merger;
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      -- the cash issued in the REIT merger; and

      -- the outstanding debt of Cornerstone including Cornerstone's allocable
         share of the outstanding debt of Cornerstone Partnership, as determined
         for tax purposes; and

     - Cornerstone's adjusted tax basis in its various properties and assets,
       including its interest in Cornerstone Partnership.

     In computing its taxable income for the taxable year ending on the date of
the REIT merger, Cornerstone generally would be entitled to a dividends paid
deduction equal to the fair market value of the Equity Office common shares and
cash, including cash paid for fractional shares, issued in the REIT merger.

     A Cornerstone stockholder would recognize gain equal to the difference
between:

     - the aggregate fair market value of the Equity Office common shares and
       the cash received; and

     - the stockholder's adjusted tax basis in its Cornerstone stock.

     To the extent that Cornerstone's gain, if any, were to exceed the fair
market value of the Equity Office common shares and cash issued in the REIT
merger, the gain generally would be taxable to Cornerstone, and the liability
for this tax would transfer to Equity Office.

     As a condition to the REIT merger, Equity Office will receive an opinion
from King & Spalding, counsel to Cornerstone, that Cornerstone qualifies as a
REIT at the time of the REIT merger. This opinion, however, will not be binding
on the Internal Revenue Service or the courts. If Cornerstone did not qualify as
a REIT at the time of the REIT merger, Cornerstone would be required to
recognize gain with respect to the built-in gain attributable to its assets.
Built-in gain is the amount by which an asset's fair market value exceeds its
adjusted tax basis. As the successor to Cornerstone in the REIT merger, Equity
Office would be liable for any tax owed by Cornerstone as a result of the
recognition of built-in gain. However, under recently published Treasury
Regulations, Equity Office would be able to make an election that would allow
Cornerstone to avoid recognizing its built-in gain if Cornerstone did not
qualify as a REIT at the time of the REIT merger. This election would require
Equity Office to recognize the built-in gain at the highest regular corporate
rate if Equity Office were to dispose of any asset with built-in gain that was
acquired from Cornerstone during the 10 years following the REIT merger. Even
though Equity Office will receive an opinion of King & Spalding, counsel to
Cornerstone, that Cornerstone qualifies for taxation as a REIT at the time of
the REIT merger, Equity Office intends to make a protective election of the type
described above as a precautionary measure in order to ensure that Cornerstone
would not recognize gain at the time of the REIT merger if the Internal Revenue
Service later were to determine that Cornerstone did not qualify as a REIT at
the time of the REIT merger.

     REIT Qualification. Both Equity Office and Cornerstone have elected to be
taxed as REITs under sections 856 through 860 of the Internal Revenue Code. A
REIT generally is not subject to federal income tax on the income that it
distributes to shareholders if it distributes at least 95% of its REIT taxable
income and it meets other requirements. For taxable years starting after
December 31, 2000, REITs will have to distribute only 90% of their REIT taxable
income to shareholders.

     As a condition to the REIT merger, Hogan & Hartson L.L.P., counsel to
Equity Office, will deliver an opinion to Cornerstone that commencing with
Equity Office's taxable year ending December 31, 1997, Equity Office was
organized and has operated in conformity with the requirements for qualification
as a REIT, and that after consummation of the REIT merger, Equity Office's
proposed method of operation will enable it to continue to qualify as a REIT.

     This opinion will rely upon customary representations made by Equity Office
about factual matters relating to the organization and operation of Equity
Office, EOP Partnership and its subsidiaries, including BeaMetFed, Inc. In
addition, this opinion will be based upon factual representations of Equity
Office concerning its business and properties as set forth in this joint proxy
statement/prospectus and the other documents incorporated by reference in this
joint proxy statement/ prospectus. Finally, the portion of the

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Hogan & Hartson L.L.P. opinion that addresses the qualification of Equity Office
as a REIT following the REIT merger will be based in part upon the opinion of
King & Spalding relating to the qualification of Cornerstone as a REIT at the
closing of the REIT merger and the representations made by Cornerstone in
connection with the King & Spalding opinion.

     Equity Office intends to continue to operate in a manner to qualify as a
REIT following the REIT merger, but there is no guarantee that Equity Office
will qualify or remain qualified as a REIT. Qualification and taxation as a REIT
depend upon Equity Office's ability to meet, through actual annual operating
results, requirements relating to asset ownership, distribution levels and
diversity of share ownership, and the various REIT qualification requirements
imposed under the Internal Revenue Code. Hogan & Hartson L.L.P. will not review
Equity Office's compliance with these tests on a continuing basis. Given the
complex nature of the REIT qualification requirements, the ongoing importance of
factual determinations and the possibility of future changes in the
circumstances of Equity Office, Equity Office cannot guarantee that its actual
operating results for any particular tax year will satisfy the requirements for
taxation as a REIT under the Internal Revenue Code.

     If Cornerstone did not qualify as a REIT in any of its prior tax years,
Cornerstone will become liable for federal income tax on its income earned in
any year it did not qualify as a REIT. In addition, if Cornerstone did not
qualify as a REIT at the time of the REIT merger, Equity Office could have to
pay additional taxes if it sold any of the Cornerstone properties within 10
years following the REIT merger. As a condition to the REIT merger, King &
Spalding, counsel to Cornerstone, will provide an opinion to Equity Office that
Cornerstone, commencing with its taxable year ended December 31, 1997 through
its short taxable year ending at the closing of the REIT merger, was organized
and has operated in conformity with the requirements for qualification as a
REIT. This opinion will rely upon customary representations made by Cornerstone
about factual matters relating to the organization and operation of Cornerstone,
Cornerstone Partnership and their affiliates. Cornerstone intends to continue to
operate in a manner to qualify or remain qualified as a REIT until the closing
of the REIT merger. Qualification and taxation as a REIT depend upon
Cornerstone's ability to meet, through actual annual operating results,
requirements relating to asset ownership, distribution levels and diversity of
share ownership, and the various REIT qualification requirements imposed under
the Internal Revenue Code. There is no guarantee that Cornerstone's actual
operating results for any of its taxable years, including its short taxable year
ending at the closing of the REIT merger, will have satisfied the requirements
for taxation as a REIT under the Internal Revenue Code.

     To qualify as a REIT, Equity Office cannot have at the end of any taxable
year any undistributed earnings and profits that are attributable to a non-REIT
taxable year. As a result of the REIT merger, Equity Office will inherit any
undistributed non-REIT earnings and profits that would result from the failure
of Cornerstone to qualify as a REIT at any point. Equity Office will receive an
opinion from King & Spalding regarding Cornerstone's REIT qualification, which
will rely on Cornerstone's representations to King & Spalding that Cornerstone
does not have any non-REIT earnings and profits attributable to any taxable year
in which Cornerstone did not elect or qualify to be taxed as a REIT, and that
Cornerstone will take all steps to ensure that it will not have earnings and
profits attributable to non-REIT taxable years at the close of Cornerstone's
short taxable year ending at the time of the REIT merger.

     Other information relevant to Equity Office's REIT qualification. In order
to qualify as a REIT, Equity Office also must derive at least 95% of its gross
income from specified qualifying sources. Following the REIT merger, Equity
Office intends to operate the former Cornerstone properties in a manner so that
they do not produce material amounts of non-qualifying income. After the REIT
merger, Equity Office will own and operate a hotel property currently owned by
Cornerstone. Income from the operation of a hotel does not qualify for purposes
of the REIT income tests. Equity Office intends either to transfer or lease this
property to one of its non-controlled subsidiaries. Equity Office believes that
the amount of nonqualifying income generated from this hotel will be an
insignificant amount and will not affect Equity Office's ability to meet the 95%
gross income test.

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     In addition, in order to qualify as a REIT, Equity Office cannot own more
than 10% of the voting securities of any issuer, and it cannot have more than 5%
of its assets invested in the stock and securities of any one issuer. Equity
Office will acquire in the REIT merger a new non-controlled subsidiary, WCP
Services, Inc., currently owned by Cornerstone. Equity Office will own all of
the non-voting stock and 1% of the voting stock of WCP Services, Inc., which
together represents 95% of the economic interest. The remaining voting stock
representing 5% of the economic interest will be acquired by Equity Office
Property Management Corp., another non-controlled subsidiary of Equity Office.
WCP Services, Inc. is taxable as a regular "C" corporation. Equity Office does
not believe that the value of the securities of WCP Services, Inc. will cause it
to violate the 5% asset test.

                      BUSINESS OF CORNERSTONE PARTNERSHIP

GENERAL

     Cornerstone is a self-administered equity real estate investment trust
which owns, through Cornerstone Partnership, interests in 82 class A office
buildings comprising approximately 18 million rentable square feet, a shopping
center, a hotel and developable land. These properties are primarily located in
nine major metropolitan areas throughout the United States: Atlanta, Boston,
suburban Chicago, Minneapolis, New York City, San Francisco Bay Area, Seattle,
Southern California and Washington, D.C. and surrounding suburbs. In January
1998, Cornerstone converted its corporate structure into an umbrella limited
partnership REIT. Under this structure, Cornerstone owns all of its properties
and conducts all of its business through Cornerstone Partnership. Cornerstone is
the sole general partner of Cornerstone Partnership and owns approximately 87.1%
of the Cornerstone Partnership units.

     Cornerstone Partnership is a Delaware limited partnership formed in
December 1997. Cornerstone Partnership's principal place of business is located
at Tower 56, 126 East 56th Street, New York, New York 10022. Cornerstone has an
internet web site at http://www.cstoneprop.com.

OPERATIONS

     The operations of the Cornerstone Partnership properties are conducted
under the direction of Cornerstone, which is managed by its executive officers
and board of directors.

OWNERSHIP AND MANAGEMENT OF CORNERSTONE PARTNERSHIP PROPERTIES

     All of the properties, with the exception of 191 Peachtree Street,
Washington Mutual Tower, Norwest Center, 500 Boylston Street, 222 Berkeley
Street, Market Square, 120 Montgomery Street, and One Post, all of which are
referred to herein as the "joint venture properties," are owned directly or
indirectly by Cornerstone Partnership. Cornerstone Partnership owns only a
partial interest in the joint venture properties. Consequently, Cornerstone
Partnership may not exercise sole decision-making authority with respect to the
joint venture properties.

     Cornerstone Partnership conducts third party management operations through
WCP Services, Inc., a partially-owned subsidiary of Cornerstone Partnership. WCP
Services provides management services for approximately      million square feet
of office space owned by third parties. Cornerstone Partnership owns 1% of the
voting stock and 100% of the non-voting stock of WCP Services, which
collectively represent 95% of the economic value of WCP Services.

     Cornerstone Partnership believes that all of the Cornerstone Partnership
properties are adequately covered by insurance. Fifty-nine of the Properties are
located in California, an area of particular earthquake risk. Cornerstone
Partnership carries earthquake insurance on all of its properties located in
California; the policies, however, are subject to coverage limitations.

                                       102
<PAGE>   115

     The following table summarizes Cornerstone Partnership's interest in real
estate investments at December 31, 1999. None of the properties listed below had
either net book values equal to 10.0% or more of Cornerstone Partnership's total
assets as of December 31, 1999 or gross revenues equal to 10.0% or more of
Cornerstone Partnership's consolidated gross revenues for the year ended
December 31, 1999.

<TABLE>
<CAPTION>
                                                               CORNERSTONE
                MARKET NAME                   TOTAL RENTABLE   PARTNERSHIP       YEAR
                  PROPERTY                     SQUARE FEET     INTEREST (A)   CONSTRUCTED   LEASED   NOTES
                -----------                   --------------   ------------   -----------   ------   -----
<S>                                           <C>              <C>            <C>           <C>      <C>
BOSTON, MASSACHUSETTS
  Sixty State Street                               823,014        100.0%         1979        100%       B
  500 Boylston Street                              714,513         91.5%         1988        100%       C
  222 Berkeley Street                              530,844         91.5%         1991        100%       C
  125 Summer Street                                463,691        100.0%         1989         74%
  One Memorial Drive                               352,764        100.0%         1985        100%       D
                                                ----------                                   ---
  MARKET TOTAL                                   2,884,826                                    96%
SAN MATEO COUNTY, CALIFORNIA
  Bayhill (4 buildings)                            514,255        100.0%      1982-1987       96%       E
  Peninsula Office Park (7 buildings)              492,044        100.0%      1971-1998      100%       E
  Seaport Centre                                   463,418        100.0%         1988        100%       E
  Bay Park Plaza (2 buildings)                     257,058        100.0%      1985-1998      100%       E
  One Bay Plaza                                    176,533        100.0%         1979         99%       E
                                                ----------                                   ---
  MARKET TOTAL                                   1,903,308                                    99%
ATLANTA, GEORGIA
  191 Peachtree Street                           1,215,288         80.0%         1991         98%     C,F
  200 Galleria                                     432,698        100.0%         1985         98%       C
                                                ----------                                   ---
  MARKET TOTAL                                   1,647,986                                    98%
EAST BAY, CALIFORNIA
  Corporate Centre (2 buildings)                   329,348        100.0%      1985-1987       96%       E
  ADP Plaza (2 buildings)                          300,308        100.0%      1987-1989       95%       E
  PeopleSoft Plaza                                 277,562        100.0%         1984        100%       E
  Norris Tech Center (3 buildings)                 260,513        100.0%      1984-1990      100%       E
  Golden Bear Center                               160,587        100.0%         1986         99%       E
  2700 Ygnacio Valley Road                         103,214        100.0%         1984         99%       E
  Park Plaza                                        87,040        100.0%         1986        100%       E
  1600 South Main                                   83,277        100.0%         1983         98%       E
                                                ----------                                   ---
  MARKET TOTAL                                   1,601,849                                    98%
SEATTLE, WASHINGTON
  Washington Mutual Tower (3 buildings)          1,154,560         50.0%         1988         98%       G
  110 Atrium Place                                 215,172        100.0%         1981        100%       E
  Island Corporate Center                          100,009        100.0%         1987         97%       E
                                                ----------                                   ---
  MARKET TOTAL                                   1,469,741                                    98%
SANTA CLARA COUNTY, CALIFORNIA
  Pruneyard Office (3 buildings)                   354,629        100.0%      1971-1999       99%     E,H
  10 Almaden                                       294,809        100.0%         1989        100%       E
  Pruneyard Shopping Center                        252,210        100.0%        1970s         90%       E
  Embarcadero Place (4 buildings)                  192,081        100.0%         1984        100%       E
  Pruneyard Inn                                     94,500        100.0%         1989        N/A      E,I
                                                ----------                                   ---
  MARKET TOTAL                                   1,188,229                                    98%
</TABLE>

                                       103
<PAGE>   116

<TABLE>
<CAPTION>
                                                               CORNERSTONE
                MARKET NAME                   TOTAL RENTABLE   PARTNERSHIP       YEAR
                  PROPERTY                     SQUARE FEET     INTEREST (A)   CONSTRUCTED   LEASED   NOTES
                -----------                   --------------   ------------   -----------   ------   -----
<S>                                           <C>              <C>            <C>           <C>      <C>
SAN FRANCISCO, CALIFORNIA
  120 Montgomery Street                            420,310         66.7%         1955         95%       E
  One Post                                         391,450         50.0%         1969         99%       E
  201 California Street                            240,230        100.0%         1980         96%       J
  188 Embarcadero                                   85,183        100.0%         1985         99%       E
                                                ----------                                   ---
  MARKET TOTAL                                   1,137,173                                    97%
MINNEAPOLIS, MINNESOTA
  Norwest Center                                 1,117,439         50.0%         1988        100%       K
                                                ----------                                   ---
  MARKET TOTAL                                   1,117,439                                   100%
WASHINGTON, D.C./ALEXANDRIA, VIRGINIA
  Market Square (2 buildings)                      688,709         70.0%         1990         99%     C,L
  99 Canal Center                                  137,945        100.0%         1986        100%       C
  TransPotomac Plaza 5                              96,392        100.0%         1983        100%       C
  11 Canal Center                                   70,365        100.0%         1986         98%       C
                                                ----------                                   ---
  MARKET TOTAL                                     993,411                                    99%
SUBURBAN CHICAGO, ILLINOIS
  Corporate 500 Centre (4 buildings)               679,039        100.0%      1986/1990       99%       M
  One Lincoln Centre                               297,040        100.0%         1986         89%
                                                ----------                                   ---
  MARKET TOTAL                                     976,079                                    96%
SANTA MONICA/WEST LOS ANGELES, CALIFORNIA
  West Wilshire (2 buildings)                      235,787        100.0%      1960-1976       94%       E
  Wilshire Palisades                               186,714        100.0%         1981        100%       J
  Janss Court                                      125,709        100.0%         1989        100%     E,N
  Searise Office Tower                             122,292        100.0%         1975        100%       E
  Commerce Park                                     94,367        100.0%         1977         79%     E,O
  429 Santa Monica                                  83,243        100.0%         1982         88%       E
                                                ----------                                   ---
  MARKET TOTAL                                     848,112                                    95%
ORANGE COUNTY, CALIFORNIA
  Bixby Ranch                                      277,289        100.0%         1987         98%       E
  18301 Von Karman                                 219,508        100.0%         1991         88%       E
  2677 North Main                                  213,318        100.0%         1987         94%       E
                                                ----------                                   ---
  MARKET TOTAL                                     710,115                                    94%
SAN DIEGO, CALIFORNIA
  Centerside II                                    286,949        100.0%         1987         93%       E
  Crossroads                                       133,553        100.0%         1983        100%       E
                                                ----------                                   ---
  MARKET TOTAL                                     420,502                                    95%
NEW YORK CITY, NEW YORK
  527 Madison Avenue                               215,332        100.0%         1986        100%
  Tower 56                                         163,633        100.0%         1983         99%       P
                                                ----------                                   ---
  MARKET TOTAL                                     378,965                                    99%
LOS ANGELES, CALIFORNIA
  700 North Brand                                  202,531        100.0%         1981         94%       E
  Warner Park Center                                57,366        100.0%         1986        100%       E
                                                ----------                                   ---
  MARKET TOTAL                                     259,897                                    95%
CONEJO VALLEY (VENTURA), CALIFORNIA
  Westlake Spectrum (2 buildings)                  118,990        100.0%         1990         97%       E
  Agoura Hills                                     115,208        100.0%         1987        100%       E
                                                ----------                                   ---
  MARKET TOTAL                                     234,198                                    99%
</TABLE>

                                       104
<PAGE>   117

<TABLE>
<CAPTION>
                                                               CORNERSTONE
                MARKET NAME                   TOTAL RENTABLE   PARTNERSHIP       YEAR
                  PROPERTY                     SQUARE FEET     INTEREST (A)   CONSTRUCTED   LEASED   NOTES
                -----------                   --------------   ------------   -----------   ------   -----
<S>                                           <C>              <C>            <C>           <C>      <C>
OTHER REGIONS
  U.S. West (Murray, Utah)                         136,608        100.0%         1985         76%       E
  Exposition Centre (Sacramento, California)        72,971        100.0%         1984         70%       E
                                                ----------                                   ---
  MARKET TOTAL                                     209,579                                    74%
                                                ----------                                   ---
  TOTAL PORTFOLIO                               17,981,409                                    97%
                                                ----------                                   ---
  Minority Interest Adjustment (Q)                (728,307)
                                                ----------                                   ---
  CORNERSTONE PORTFOLIO                         17,253,102                                    96%
                                                ==========                                   ===
</TABLE>

- ---------------
(A) Unless noted below, cash flow and residual proceeds will be distributed to
    Cornerstone Partnership according to its percentage interest.

(B) On December 31, 1997, Cornerstone purchased the second mortgage on Sixty
    State Street. The mortgage is a cash flow mortgage through which all the
    economic benefits/risks (subject to the first mortgage) inure to Cornerstone
    Partnership. Cornerstone Partnership controls all major decisions regarding
    management and leasing. The total purchase price for the second mortgage was
    $131.5 million and is consolidated in buildings due to the above factors.
    The $78.4 million first mortgage on the property was originally recorded by
    Cornerstone as an $89.6 million liability due to its above-market interest
    rate. As of January 20, 1998 all of the interests stated above were
    contributed to Cornerstone Partnership in exchange for units.

    The second mortgage, which Cornerstone Partnership holds, is collateralized
    only by the improvements on Sixty State Street. Title to the improvements is
    owned by Sixty State Street Trust, the ground lessee under a ground lease
    that expires on December 28, 2067. The lease payments on the ground lease
    are $398,896 per annum throughout the term.

(C) On October 27, 1997, Cornerstone acquired interests in nine Class A office
    properties comprising approximately 4.5 million rentable square feet in
    Alexandria, Virginia (3 properties), Atlanta (2 properties), Boston (2
    properties), Charlotte and Washington, D.C., as well as an undeveloped
    parcel of land in Chicago, which we refer to as the DIHC Portfolio.
    Cornerstone acquired the DIHC Portfolio for a purchase price of
    approximately $1.06 billion, consisting of approximately 34.2 million shares
    of Cornerstone common stock valued and recorded at $16.00 per share,
    approximately $260.0 million in cash and $250.0 million in promissory notes.
    The cash portion of the acquisition was financed with proceeds from
    Cornerstone's initial public offering in April 1997 and $54.0 million from
    its revolving credit facility. As of January 20, 1998 all of the interests
    stated above were contributed to Cornerstone Partnership in exchange for
    units. Cornerstone Partnership has since sold the asset in Charlotte as well
    as the undeveloped parcel of land in Chicago.

(D) On April 28, 1998, Cornerstone Partnership purchased One Memorial Drive in
    Cambridge, Massachusetts. The total purchase price for the property was
    approximately $112.5 million, approximately $23.5 million of which was paid
    in cash, approximately $29.0 million of which was paid in Cornerstone
    Partnership units valued at $17.50 per unit and approximately $60.0 million
    of which was paid in Cornerstone's common stock valued at $17.50 per share.

(E) This property was acquired as a result of the Wilson acquisition in December
    1998. After receiving stockholder approval on December 14, 1998, Cornerstone
    Partnership acquired substantially all of the properties and real estate
    operations of William Wilson & Associates and related entities, or WW&A. We
    refer to this acquisition as the Wilson acquisition. As part of the Wilson
    acquisition, Cornerstone Partnership acquired interests in 69 Class A office
    properties, comprising approximately 9.2 million rentable square feet
    primarily in the San Francisco Bay Area and in Southern California, a
    shopping center consisting of approximately 252,000 rentable square feet in
    Santa Clara, California, a hotel consisting of 94,500 square feet in Santa
    Clara, California and 12.8 acres of developable land in the

                                       105
<PAGE>   118

    San Francisco Bay Area. Cornerstone Partnership has since sold eleven assets
    comprising approximately 1.2 million square feet.

    Cornerstone and Cornerstone Partnership acquired WW&A for a purchase price
    of approximately $1.8 billion, consisting of approximately 14.9 million
    shares of Cornerstone's common stock valued at $17.25 per share (recorded at
    $16.25 per share for GAAP purposes), approximately 16.2 million Cornerstone
    Partnership units valued at $17.25 per unit (recorded at $16.25 per unit for
    GAAP purposes), approximately $465.0 million in cash and the assumption of
    approximately $760.0 million of property and construction related debt
    (recorded at $773.7 million for GAAP purposes). The cash portion of the
    transaction was financed primarily from Cornerstone Partnership's revolving
    credit facility and the sale of $200.0 million of Cornerstone common stock
    to PGGM, an approximate 33.6% stockholder prior to the Wilson acquisition,
    priced at $17.25 per share.

(F)  While Cornerstone Partnership's stated interest in the partnership that
     owns 191 Peachtree Street is 80.0%, its economic interest is significantly
     larger since it has acquired the first mortgage note on the property in the
     amount of $145.0 million, which earns interest at 9.375% and will receive a
     priority distribution on its acquired capital base. In 1999, the partner in
     the transaction, CH Associates, Ltd., received an annual incentive
     distribution (as defined) of $250,000, with Cornerstone Partnership
     receiving the remainder of the cash flow of the property.

     The partnership that owns 191 Peachtree Street leases a portion of the land
     upon which the project is located pursuant to a ground lease agreement. The
     agreement requires annual payments of $45,000 through January 31, 2002 and
     $75,000 through January 31, 2008. Thereafter, the annual rent increases
     $2,500 per year until the expiration date of January 31, 2087. The
     partnership records ground rental expense relating to this agreement on a
     straight-line basis. The ground lease is renewable for an additional 99
     years.

(G)  While Cornerstone Partnership's stated interest in the partnership that
     owns Washington Mutual Tower is 50.0%, its economic interest in the
     property is significantly larger due to priority distributions it receives
     on its invested capital base. For the year ended December 31, 1999, the
     Cornerstone Partnership received 100% of the cash distributions from the
     partnership that owns Washington Mutual Tower.

(H)  The final phase of the Pruneyard complex, Pruneyard Place, was completed
     and occupied on April 1, 1999. The building was entirely pre-leased.

(I)  The Pruneyard Inn is a three-story hotel. An expansion was completed in May
     1999, increasing the number of rooms from 118 to 172.

(J)   On June 3, 1998, Cornerstone Partnership purchased 201 California Street
      and Wilshire Palisades. The total purchase price for the properties was
      approximately $121.5 million, approximately $29.5 million of which was
      paid in cash, approximately $29.1 million of which was paid in Cornerstone
      Partnership units valued at $17.50 per unit and approximately $62.9
      million of assumed debt (recorded at $64.6 million for GAAP purposes).

(K)  While Cornerstone Partnership's stated interest in the partnership that
     owns Norwest Center is 50.0%, its economic interest in the property is
     significantly larger due to priority distributions it receives on its
     invested capital base. For the year ended December 31, 1999, Cornerstone
     Partnership's share of earnings and cash distributions from the partnership
     that owns Norwest Center was 74.4%.

(L)  During 1998, through a series of transactions, Cornerstone Partnership
     acquired partnership interests with a stated interest of approximately
     70.0% in the partnerships that own Market Square. Cornerstone Partnership's
     economic interest is significantly larger since it has acquired the first
     mortgage note on the property in the amount of $181.0 million which earns
     interest at 9.75% and will receive a priority distribution on its acquired
     capital base. In addition, Cornerstone Partnership acquired a "buffer
     loan," with accrued principal and interest of $49.0 million at purchase,
     which accrues interest at a rate of prime plus 1.25% and is payable from
     cash flow, refinancing or sales proceeds in excess of the first mortgage.
     During the year ended December 31, 1999, Cornerstone Partnership received
     100% of the cash flow from the property. On November 14, 1998, Cornerstone

                                       106
<PAGE>   119

     Partnership purchased an additional interest in the partnerships that own
     Market Square which enabled it to gain sufficient control in order to
     consolidate the investment.

(M)  On January 28, 1998, Cornerstone Partnership purchased Corporate 500 Centre
     in Deerfield, Illinois. This property consists of four Class A office
     buildings with approximately 679,000 rentable square feet. The
     consideration paid for this property was approximately $135.0 million in
     cash and approximately $15.0 million in Cornerstone Partnership units
     valued at $18.50 per unit, for a total purchase price of approximately
     $150.0 million. Cornerstone Partnership financed a portion of the purchase
     price with an $80.0 million mortgage loan from Bankers Trust Company, which
     mortgage was subsequently refinanced in October 1998.

(N)  Janss Court is a seven-story class A mixed-use building containing
     approximately 126,000 square feet. In addition to approximately 93,000
     square feet of retail and office space, Janss Court offers 32 apartments
     for a total of 33,000 rentable square feet of residential space.

(O)  The property is subject to a ground lease agreement. The agreement requires
     annual payments of $115,000 through March 31, 2002 and $121,000 from April
     1, 2002 through March 31, 2007. The lease payment increases every ten years
     thereafter according to a formula based on the Consumer Price Index. The
     ground lease expires on March 31, 2041.

(P)  On January 5, 1998, Cornerstone purchased for approximately $5.5 million,
     the remaining participation rights in the cash flow and residual value of
     Tower 56 from the former participants for 307,692 shares of Cornerstone
     common stock. As a result, all of the cash flow and the residual value of
     Tower 56 inures to Cornerstone Partnership. As of January 20, 1998 all of
     the interests stated above were contributed to Cornerstone Partnership in
     exchange for Cornerstone Partnership units.

(Q)  Rentable square feet includes an adjustment for the interest of a joint
     venture or minority partner. Calculations are based on the partners'
     percentage interest in the cash flows of the property.

TENANTS

     Cornerstone Parnership's tenants include local, regional, national and
international companies engaged in a variety of businesses. The following table
sets forth, as of December 31, 1999, information concerning the ten largest
tenants ranked by their respective percentages of Cornerstone Partnership's
aggregate annualized rent. Annualized rent is the monthly contractual base rent
under existing leases as of December 31, 1999, multiplied by 12.

<TABLE>
<CAPTION>
                                              WEIGHTED
                                               AVERAGE           PERCENTAGE                      PERCENTAGE OF
                                              REMAINING         OF AGGREGATE        AGGREGATE      AGGREGATE
                                NUMBER OF    LEASE TERM     PORTFOLIO ANNUALIZED    RENTABLE       OCCUPIED
          TENANT (a)            BUILDINGS   IN MONTHS (b)         RENT (c)         SQUARE FEET    SQUARE FEET
          ----------            ---------   -------------   --------------------   -----------   -------------
<S>                             <C>         <C>             <C>                    <C>           <C>
Norwest Corporation (Wells
  Fargo)                            4            181                 2.8%             795,424         4.6%
Massachusetts Financial
  Services                          1             38                 2.4%             328,540         1.9%
Hale & Dorr                         1            162                 2.4%             319,501         1.9%
Wachovia Bank                       1            108                 2.2%             380,442         2.2%
King & Spalding                     1            109                 2.0%             314,443         1.8%
The New England Life                2            105                 1.3%             216,978         1.3%
Perkins Coie                        1            132                 1.2%             240,127         1.4%
Houghton Mifflin                    1             86                 1.1%             225,883         1.3%
PeopleSoft Corporation              1            105                 1.0%             210,940         1.2%
McKesson HBOC, Inc.                 1            157                 0.6%             132,476         0.8%
                                                 ---                ----            ---------        ----
     TOTAL WEIGHTED AVERAGE
       (b)                                       123                17.0%           3,164,754        18.4%
                                                 ===                ====            =========        ====
</TABLE>

- ---------------
(a) Actual tenant may be a subsidiary of, or an entity affiliated with, the
    named tenant.

(b) Weighted average calculation based on aggregate rentable square footage
    occupied by each tenant.

                                       107
<PAGE>   120

(c) "Annualized Rent" is the monthly contractual base rent under existing leases
    as of December 31, 1999 multiplied by 12.

RECENT DEVELOPMENTS

     Property Dispositions. In 1999, Cornerstone Partnership sold its interest
in 13 office properties for gross proceeds of $495,705,000, comprising
approximately 3.0 million rentable square feet in Charlotte, Denver, Phoenix
(four properties), the San Francisco Bay Area (six properties) and Southern
California. Also during 1999, Cornerstone Partnership acquired a six-acre
development project in the San Francisco Bay Area for approximately $36 million.
On March 15, 2000 and March 23, 2000, Cornerstone Partnership sold its interest
in two properties located in East Bay, California for gross proceeds of
$14,425,000 and $12,800,000, respectively. The properties had been acquired as
part of the Wilson acquisition in December 1998.

     Prudential/Northwestern Debt Restructuring. On June 23, 1999, Cornerstone
Partnership restructured approximately $163.0 million of property-related debt
with Prudential Insurance of Company of America and Northwestern Mutual Life
Insurance Company. The restructuring involved retiring 17 of the individual
property-related debts and creating a single $180.0 million term loan which is
cross-collateralized by six of Cornerstone Partnership's properties. The loan
has a ten-year term and bears interest at 7.26% per annum.

     Northwestern Debt Restructuring. On October 6, 1999, Cornerstone
Partnership restructured approximately $219.9 million of individual
property-related debt with Northwestern Mutual Life Insurance Company. The
restructuring involved retiring the individual property-related debt and
creating a single $275.0 million term loan which is cross-collateralized by five
of the original six properties. The loan has a ten-year term and bears interest
at 7.23%. Upon closing the loan, the lien on 10 Almaden was released and the
property was added to Cornerstone Partnership's unencumbered pool.

     Development Project Modification. In April 1998, Cornerstone Partnership
entered into a contract to acquire from the developer the 928,857 square-foot
Piper Jaffray building under construction in Minneapolis. In November 1999, this
contract was amended in connection with a 350,000 square-foot expansion lease
with a major tenant of the building. The contract was amended to provide for a
purchase price equal to the costs incurred in construction and development plus
a fixed amount to the developer plus an additional amount based on the leasing
of the building. In addition, at Cornerstone Partnership's election, the closing
of the acquisition may occur prior to the completion of the building, but the
developer will remain obligated to complete the project.

     400 Capitol Mall Acquisition. On January 21, 2000, Cornerstone Partnership
purchased 400 Capitol Mall in Sacramento, California. This property contains
approximately 502,000 rentable square feet. The total purchase price for the
property was approximately $130.0 million, consisting of approximately $128.0
million in cash which were section 1031 exchange funds from the sale of One
Norwest Center in Denver, Colorado, and approximately $2.0 million of which was
paid in Cornerstone Partnership units valued at $17.25 per unit.

COMPETITION

     The leasing of real estate is highly competitive. Cornerstone Partnership's
properties compete for tenants with similar properties located in its markets
primarily on the basis of location, rent charged, services provided and the
design and condition of the improvements.

                                       108
<PAGE>   121

MORTGAGE INDEBTEDNESS

     The following table sets forth certain information regarding the
consolidated debt obligations of Cornerstone Partnership as of December 31, 1999
and 1998, including mortgage obligations relating to the properties. All of this
debt is nonrecourse to Cornerstone Partnership. However, notwithstanding the
nonrecourse indebtedness, the lender may have the right to recover deficiencies
from Cornerstone Partnership in certain circumstances, including fraud,
misappropriation of funds and environmental liabilities (dollar amounts in
thousands).

<TABLE>
<CAPTION>
                                                                        MATURITY
PROPERTY                        AMORTIZATION    INTEREST RATE (A)         DATE          12/31/99     12/31/98
- --------                        -------------   -----------------      ----------      ----------   ----------
<S>                             <C>             <C>                    <C>             <C>          <C>
FIXED RATE DEBT
TransPotomac Plaza (B)........  Interest Only               7.28%        Oct-2000      $   65,000   $   65,000
West Wilshire Office and
  Medical.....................        25 year               6.90%        Jan-2002          16,926       17,301
Searise Office Tower..........        25 year               6.90%        Jan-2002          11,607       11,864
Exposition Centre.............        25 year               6.90%        May-2002           5,081        5,200
Wilshire Palisades............        22 year               6.70%        Jul-2002          29,047       29,902
110 Atrium Place..............        30 year               6.90%        Mar-2004          21,517       21,838
527 Madison Avenue and
  One Lincoln Centre (B)......  Interest only               7.47%        Oct-2004          65,000       65,000
Sixty State Street............        30 year               6.84%        Jan-2005          85,420       87,627
Island Corporate Center.......        30 year               6.90%        Apr-2005          13,170       13,294
Washington Mutual Tower.......  Interest only               7.53%        Nov-2005          79,100       79,100
Norwest Center................  Interest only               8.74%        Dec-2005         110,000      110,000
Agoura Hills..................        25 year               6.90%        Dec-2005          12,003       12,328
Janss Court...................        30 year               6.90%        Dec-2005          18,357       18,723
Bayhill 4, 5, 6 & 7...........        25 year               6.90%        Dec-2006          57,764       59,071
Market Square (C) and
  200 Galleria (B)............  Interest only               7.54%        Oct-2007         120,000      120,000
Corporate 500 Centre..........        25 year               6.66%        Nov-2008          88,424       89,765
188 Embarcadero (D)...........        25 year               7.26%        Aug-2009          15,606        9,135
Centerside II (D).............        25 year               7.26%        Aug-2009          24,254       13,818
700 North Brand (D)...........        25 year               7.26%        Aug-2009          26,938       18,108
Golden Bear Center (D)........        25 year               7.26%        Aug-2009          20,477       15,753
Bixby Ranch (D)...............        25 year               7.26%        Aug-2009          28,528       20,243
One Memorial Drive (D)........        25 year               7.26%        Aug-2009          63,119           --
125 Summer Street (E).........        25 year               7.23%        Nov-2009          78,844       50,000
Tower 56 (E)..................        25 year               7.23%        Nov-2009          25,024       17,548
Peninsula Office Park 1, 3, 4,
  5, 6, 8 & 9 (E).............        25 year               7.23%        Nov-2009          88,128       60,242
Embarcadero Place (E).........        25 year               7.23%        Nov-2009          38,149       26,061
201 California Street (E).....        25 year               7.23%        Nov-2009          44,504       33,071
                                                                                       ----------   ----------
    Total Fixed Rate Debt.....                              7.31%(F)      7.1 yrs(F)   $1,251,987   $1,069,992
                                                                                       ----------   ----------

VARIABLE RATE DEBT
Seaport Centre (G)............  Interest only    LIBOR plus 1.50%        Dec-2000          58,000       58,000
The Pruneyard.................        24 year    LIBOR plus 1.50%        Jul-2000          60,947       49,384
120 Montgomery Street.........        24 year    LIBOR plus 1.40%        Nov-2002          48,160       46,930
Norris Tech Center............        25 year    LIBOR plus 1.65%        Dec-2003          16,066       16,392
Other loans...................        Various            Various          Various             245          597
                                                                                       ----------   ----------
    Total Variable Rate
      Debt....................                              7.48%(F)      1.5 yrs(F)   $  183,418   $  171,303
                                                                                       ----------   ----------
</TABLE>

                                       109
<PAGE>   122

<TABLE>
<CAPTION>
                                                                        MATURITY
PROPERTY                        AMORTIZATION    INTEREST RATE (A)         DATE          12/31/99     12/31/98
- --------                        -------------   -----------------      ----------      ----------   ----------
<S>                             <C>             <C>                    <C>             <C>          <C>
REPAID DEBT
18301 Von Karman (H)..........             --                 --               --              --       10,647
1600 South Main (H)...........             --                 --               --              --        5,038
Biltmore Lakes (H)............             --                 --               --              --       11,468
Belmont Shores (H)............             --                 --               --              --        9,839
2677 North Main (H)...........             --                 --               --              --       10,774
2700 Ygnacio Valley Road
  (H).........................             --                 --               --              --        5,035
Westlake Spectrum (H).........             --                 --               --              --        3,993
Park Plaza (H)................             --                 --               --              --        4,940
Warner Park Center (H)........             --                 --               --              --        5,213
429 Santa Monica (H)..........             --                 --               --              --       10,176
Crossroads (H)................             --                 --               --              --        7,339
Westlake Spectrum II (H)......             --                 --               --              --        5,284
Two ADP Plaza (I).............             --                 --               --              --       13,400
Two Corporate Centre (I)......             --                 --               --              --       18,600
One & Two Gateway (J).........             --                 --               --              --        8,679
Scottsdale Centre (J).........             --                 --               --              --        7,745
66 Bovet (J)..................             --                 --               --              --        3,939
One Norwest Center (K)........             --                 --               --              --       98,252
1300 South El Camino (J)......             --                 --               --              --        4,007
10 Almaden (L)................             --                 --               --              --       33,885
                                                                                       ----------   ----------
    Total Repaid Debt.........                                                         $       --   $  278,253
                                                                                       ----------   ----------
Total Cornerstone Partnership
  Debt before Adjustments.....                              7.33%(F)      6.4 yrs(F)   $1,435,405   $1,519,548
                                                                                       ----------   ----------
Adjustments:
One Post (M)..................        25 year               6.90%          Dec-02          17,220       17,250
120 Montgomery (N)............        24 year    LIBOR plus 1.40%          Nov-02         (16,037)     (15,646)
Norwest Center (N)............  Interest only               8.74%          Dec-05         (28,215)     (24,310)
                                                                                       ----------   ----------
Total Adjustment..............                                                         $  (27,032)  $  (22,706)
                                                                                       ----------   ----------
Total Cornerstone Partnership
  Share of Debt...............                              7.30%(F)      6.4 yrs(F)   $1,408,373   $1,496,842
                                                                                       ==========   ==========
</TABLE>

- ---------------
(A)  The interest rate is the stated interest rate for Cornerstone Partnership
     originated debt or the prevailing market rate at the time of acquisition
     for debt assumed as part of an acquisition.

(B)  The three notes arising from the acquisition of several properties from
     PGGM are cross-collateralized, having the effect of forming a "collateral
     pool" for the underlying notes.

(C)  The collateral for this loan is a pledge of the $181.0 million first
     mortgage loan on Market Square that Cornerstone Partnership purchased from
     PGGM.

(D)  The six notes arising from the restructuring of certain debt with
     Prudential Insurance Company of America and Northwestern Mutual Life
     Insurance Company are cross-collateralized, having the effect of forming a
     "collateral pool" for the underlying notes.

(E)  The five notes arising from the restructuring of certain debt with
     Northwestern Mutual Life Insurance Company are cross-collateralized, having
     the effect of forming a "collateral pool" for the underlying notes.

(F)  Weighted-average interest rate and maturity of Cornerstone Partnership's
     long-term debt.

(G)  On December 15, 1999, through an extension and modification agreement, the
     maturity date of the $58.0 million variable rate debt held on Seaport
     Centre was extended from December 31, 1999 to December 31, 2000. All other
     terms of the note remain unchanged.

                                       110
<PAGE>   123

(H)  These 12 notes were prepaid as part of the Prudential Insurance Company of
     America and Northwestern Mutual Life Insurance Company restructuring, see
     note (D) above. All the notes had a mark to market interest rate of 6.9%
     and maturity dates ranging from April 2000 to March 2003.

(I)  On January 4, 1999, in connection with the Wilson acquisition, Cornerstone
     Partnership prepaid the notes on Two ADP Plaza and Two Corporate Centre.

(J)  These notes were prepaid in conjunction with the sale of these properties.

(K)  The note was assumed by the purchaser as of the date of closing, in
     conjunction with the sale of this property during the fourth quarter.

(L)  This note was prepaid as part of the Northwestern Mutual Life Insurance
     Company restructuring, see note (E) above. This note had a mark to market
     interest rate of 6.9% and a maturity of April 2004.

(M)  Amount relates to Cornerstone Partnership's share of property debt as this
     property is accounted for under the equity method of accounting.

(N)  Amounts relate to the joint venture or minority partners' portion of the
     total debt. Calculations are based on the partners' 1999 percentage
     participation in the cash flow of such property.

     The combined aggregate amount of maturities for all long-term borrowings
for 2000 through 2004 are $183,947,000, $0, $110,821,000, $16,066,000 and
$86,517,000, respectively.

REVOLVING CREDIT FACILITY

     Cornerstone Partnership has a $550.0 million revolving credit facility with
a syndicate of 17 banks led by Deutsche Bank, The Chase Manhattan Bank and Bank
of America for acquisitions and general working capital purposes as well as the
issuance of letters of credit, which we refer to as the revolving credit
facility. The interest rate on the facility depends on Cornerstone Partnership's
ratio of total debt to asset value (as defined) at the time of borrowing and
will be at a spread of 1.10% to 1.40% over the applicable LIBOR or prime rate at
the borrower's option. The letters of credit will be priced at the applicable
Eurodollar credit spread. The revolving credit facility expires on November 3,
2001. As of December 31, 1999, $329.0 million of the facility was outstanding at
a rate of approximately 8.0%. Of this amount, approximately $250.0 million is
fixed with interest rate swaps, which effectively fix the rate at 6.47%.
Beginning January 2000, the rate will be reduced to 5.41% through the expiration
of the swaps in December 2000. The revolving credit facility contains certain
restrictive covenants including: (a) a limitation on Cornerstone Partnership's
dividend to 90.0% of funds from operations and 110.0% of funds available for
distribution, both as defined in the agreement; (b) the percentage of total
liabilities to total property asset value (as defined) cannot exceed 55.0%; (c)
the ratio of adjusted EBITDA to interest expense may not be less than 2.00 to
1.00 through July 1, 1999 and 2.25 to 1.00 thereafter; (d) the fixed charge
coverage ratio may not be less than 1.75 to 1.00; and (e) the ratio of total
property asset value (as defined) to secured indebtedness may not be less than
2.22 to 1.00. The above terms reflect an amendment to the revolving credit
facility that occurred during 1999. The amendment allowed Cornerstone
Partnership to temporarily increase its leverage from 55.0% to 60.0% in (b)
above for a short period, which has since expired. Cornerstone Partnership also
increased its ability to enter into mortgage debt under (e) above by decreasing
the required ratio from 2.5 to 1.00 to 2.22 to 1.00.

LEGAL PROCEEDINGS

     In the ordinary course of business, Cornerstone Partnership is subject to
tenant and property related claims and other litigation. It is the opinion of
management, after consultation with outside counsel, that the resolution of
these claims will not have a material effect on the consolidated financial
condition or results of operations of Cornerstone Partnership.

                                       111
<PAGE>   124

              CORNERSTONE PARTNERSHIP MANAGEMENT'S DISCUSSION AND
           ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

     The following discussion should be read in conjunction with the selected
historical consolidated financial data of Cornerstone Partnership and the
historical consolidated financial statements and notes of Cornerstone
Partnership. See "Summary -- Partnership Merger Selected Historical Consolidated
Financial Data -- Cornerstone Partnership" on page 9 and "Cornerstone
Partnership Historical Consolidated Financial Statements" on page F-20.

     When used in the following discussion, the words "believes," "anticipates,"
and similar expressions are intended to identify "forward-looking statements."
Such statements are subject to various risks and uncertainties, which could
cause actual results to differ materially from those projected. Readers are
cautioned not to place undue reliance on these "forward-looking statements,"
which speak only as of the date hereof. Cornerstone Partnership undertakes no
obligation to publicly release the result of any revisions of these
"forward-looking statements," which may be made to reflect events or
circumstances after the date hereof or to reflect the occurrence of
unanticipated events.

RESULTS OF OPERATIONS

     Cornerstone Partnership's principal source of income is rental revenues
received through its investment in 76 fee simple investments, six real estate
partnerships, one limited liability company, one co-tenancy agreement and one
mortgage. NWC Limited Partnership, which we refer to as NWC, Third and
University Limited Partnership, which we refer to as Third Partnership, One
Ninety One Peachtree Associates, which we refer to as 191 Peachtree, Two Twenty
Two Berkeley Associates, which we refer to as 222 Berkeley, Five Hundred
Boylston West Venture, which we refer to as 500 Boylston, and Avenue Associates
Limited Partnership, which we refer to as Market Square (since November 1,
1998), have been consolidated because Cornerstone Partnership has the majority
interest in the economic benefits and is or has the right to become managing
general partner at its sole discretion. 120 Montgomery Associates, LLC, which we
refer to as 120 Montgomery, has been consolidated because Cornerstone
Partnership has the majority interest in the economic benefits and control of
the major decisions of the limited liability company. Cornerstone Partnership
has accounted for its investment in Market Square (from February 1, 1998 through
October 31, 1998) and One Post using the equity method of accounting because it
did not or, in the case of One Post, does not have sufficient control of the
day-to-day operations of the investment.

     PROPERTY RESULTS.  For the years ended December 31, 1999 and 1998 property
results can be summarized as follows (in thousands):

<TABLE>
<CAPTION>
                                                               FOR THE YEAR ENDED
                                                                  DECEMBER 31,
                                                              --------------------
                                                                1999        1998
                                                              --------    --------
<S>                                                           <C>         <C>
Office and parking rentals..................................  $607,409    $321,097
Less:
  Building operating expenses...............................   132,630      71,404
  Real estate taxes.........................................    71,554      44,184
  Depreciation and amortization.............................    96,726      57,031
                                                              --------    --------
Total operating expenses....................................   300,910     172,619
                                                              --------    --------
Total property income.......................................  $306,499    $148,478
                                                              ========    ========
</TABLE>

     The increase in property income from 1998 to 1999 of $158.0 million was due
to a net increase of $120.5 million derived from the interests in 69 properties
acquired as part of the Wilson acquisition on December 16, 1998 (Cornerstone
Partnership has since sold eleven of these properties); an increase of $14.2
million from Market Square, which was consolidated starting November 1998; an
increase of $9.4 million from four properties acquired during 1998 (Wilshire
Palisades, $2.0 million; One Memorial Drive, $2.6 million; 201 California
Street, $1.4 million; and Corporate 500 Centre, $3.4 million); and a

                                       112
<PAGE>   125

net increase of $15.6 million related to the properties held during both periods
resulting primarily from increased leasing activity, increased rental rates and
a reduction in depreciation due to fully depreciated leasing costs as well as
the discontinued recording of depreciation on properties held for sale. These
increases were offset by a $0.3 million decrease due to an asset sale during
1999 and a $1.4 million decrease at 125 Summer Street due to a large vacant
space for a portion of 1999.

     EARNINGS IN JOINT VENTURES

     The earnings in joint ventures of approximately $0.9 million in 1999 is
comprised of Cornerstone Partnership's investments in One Post and WCP Services,
Inc., both of which were acquired as part of the Wilson acquisition.

     The earnings in joint ventures of approximately $11.6 million in 1998 was
mainly due to the acquisition of the partnership interest in Market Square in
January 1998. The investment in Market Square was accounted for under the equity
method of accounting from February 1998 through October 1998 due to the lack of
sufficient control of the day-to-day operations of the investment. In November
1998, Cornerstone Partnership gained sufficient control of the investment and
began consolidating this investment. The amount attributable to Market Square of
$11.3 million is comprised of approximately $17.1 million of interest earned on
the loans, which was offset by an equity in loss of approximately $5.8 million.
The remaining $0.3 million of earnings in joint ventures is comprised of equity
earnings from Cornerstone Partnership's investments in One Post and WCP
Services, Inc.

     INTEREST AND OTHER INCOME

     Interest and other income was $8.0 million in 1999 and $6.6 million in
1998. These amounts primarily consist of interest earned from short-term
investments, tenant alteration income in 1998, lease cancellation income,
interest earned on a mortgage note receivable in 1998, a note receivable from a
partner and management fee income.

     The 1999 increase in interest and other income of $1.4 million from 1998 is
due to a $1.4 million increase in other income, a $1.5 million increase in
management fee income and a $2.0 million increase in interest earned from
short-term investments. These increases were offset by a $1.0 million decrease
in interest income from the mortgage loan and "buffer loan" on Market Square, a
$2.3 million decrease in tenant alteration income and a $0.2 million decrease in
lease cancellation income.

     INTEREST EXPENSE

     Interest expense incurred by Cornerstone Partnership was $137.0 million and
$63.4 million for 1999 and 1998, respectively.

     The increase in 1999 from 1998 of approximately $73.6 million is due to an
increase of $40.5 million from the property mortgages assumed as part of the
Wilson acquisition; an increase of $24.2 million on the revolving credit
facility mainly due to increased borrowings; a $2.4 million increase in interest
expense related to One Memorial Drive, which is included in the new $180.0
million loan that was completed in June 1999 (see "-- Mortgage Indebtedness"
below); an increase of $1.1 million on the Corporate 500 Centre loan due mainly
to the property being acquired on January 28, 1998; an increase of $1.9 million
on the 201 California Street and Wilshire Palisades loans mainly due to these
properties being acquired on June 3, 1998; an increase of $0.6 million in the
amortization of deferred financing costs; an increase of $1.1 million on the
DIHC portfolio loans due to the sale of the Dearborn land in March 1998; a net
increase of $1.0 million on the Sixty State Street, Washington Mutual Tower and
Norwest Center loans due to the Cornerstone Partnership being formed on January
20, 1998; and an increase of $1.0 million in interest expense related to 125
Summer Street and Tower 56, which were included in the new $275.0 million loan
that was completed in October 1999 (see "-- Mortgage Indebtedness" below). These
increases were offset by a $0.2 million decrease in interest on the One Norwest
Center loan due to the refinancing of this loan in September 1998.

                                       113
<PAGE>   126

     GENERAL AND ADMINISTRATIVE EXPENSES

     The aggregate amount of Cornerstone Partnership's general and
administrative expenses increased to $27.0 million in 1999 from $12.4 million in
1998. The increase of $14.6 million in 1999 from 1998 is due mainly to the
additional employees, space, systems and other support necessary to manage the
substantial growth in assets of Cornerstone Partnership during the most recent
twenty-three month period.

     GAIN (LOSS) ON SALE OF REAL ESTATE ASSETS

     During 1999, Cornerstone Partnership sold its interest in 13 office
properties for gross proceeds of $495.7 million, comprising approximately 3.0
million rentable square feet in Charlotte, Denver, Phoenix (four properties),
the San Francisco Bay Area (six properties) and Southern California, resulting
in a gain of approximately $131.0 million.

     On March 31, 1998, Cornerstone Partnership sold the Dearborn land (an
undeveloped parcel of land in Chicago that was acquired as part of the
acquisition of the PGGM portfolio in October 1997) for gross proceeds of
approximately $19.0 million, resulting in a loss of approximately $0.1 million.

     On December 29, 1998, Market Square sold a condominium unit located in
Washington D.C., for gross proceeds of approximately $0.3 million, resulting in
a gain of approximately $0.3 million.

     MINORITY INTEREST IN JOINT VENTURES

     The increase in minority interest in joint ventures from 1998 to 1999 of
$1.4 million is due to the change in the components of the joint venture
properties, as well as the increased income at the joint venture properties
which affects the allocation of minority interest to the Cornerstone
Partnership's joint venture partners.

LIQUIDITY AND CAPITAL RESOURCES

     CASH FLOW (DOLLAR AMOUNTS IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                FOR THE YEAR ENDED
                                                                   DECEMBER 31,
                                                             ------------------------
                                                                1999          1998
                                                             ----------    ----------
<S>                                                          <C>           <C>
CASH FLOW PROVIDED BY (USED IN):
Operating activities.......................................  $  223,115    $  173,612
Investing activities.......................................      52,488      (849,830)
Financing activities.......................................    (317,536)      737,830
Earnings to fixed charges ratio............................        2.84          2.06
</TABLE>

     YEAR ENDED DECEMBER 31, 1999 COMPARED TO YEAR ENDED DECEMBER 31, 1998

     Cash provided by operating activities increased to approximately $223.1
million for 1999 from $173.6 million for 1998. The increase is primarily due to
the cash flows from the interests in 69 properties acquired in the Wilson
acquisition. Cornerstone Partnership has since sold eleven of these assets.

     Cash provided by investing activities was approximately $52.5 million for
1999 whereas $849.8 million was used for 1998. The net increase in cash provided
by investing activities of $902.3 million is primarily due to the following:
during 1998 Cornerstone Partnership purchased Corporate 500 Centre for $135.0
million, One Memorial Drive for $23.5 million, 201 California Street and
Wilshire Palisades for $29.5 million, and the properties acquired in the Wilson
acquisition for $465.0 million; during 1998, Cornerstone Partnership incurred an
additional $144.2 million in additions to existing properties whereas
Cornerstone Partnership incurred $79.3 million in additions to existing
properties for the same period in 1999; and during 1999, Cornerstone Partnership
sold thirteen properties for proceeds net of escrow amounts of $136.7 million
whereas Cornerstone Partnership sold two real estate investments for proceeds of
$19.1 million during the same period in 1998. Further adding to the increase was
the net change in

                                       114
<PAGE>   127

investments in real estate joint ventures of approximately $31.4 million and a
decrease in other investments of $36.9 million during 1999. These amounts were
offset by a decrease of $1.4 million in the repayment of a notes receivable from
a related party (the note was paid off in January 1999).

     Cash used in financing activities was $317.5 million during 1999, whereas
$737.8 million of cash was provided by financing activities for 1998. The net
increase in cash used in financing activities of $1,055.3 million is due to the
following: a decrease in the amount received from unit offerings of $462.3
million (Cornerstone had a secondary offering in February 1998 of approximately
$262.3 million and an additional stock purchase by PGGM of $200.0 million
whereas there were no stock offerings during 1999); an increase in the costs
associated with the repurchase of units of approximately $4.9 million in 1999; a
decrease in borrowings under the credit facility of $437.5 million; an increase
in repayments under mortgage loans of $429.6 million; a decrease in proceeds
received from the distribution reinvestment plan of $4.4 million; an increase of
$13.1 million in debt prepayment costs; an increase of $1.2 million in
unitholder redemptions; a decrease in contributed capital from Cornerstone of
$59.7 million and an increase in distributions to minority partners and
unitholders of $0.7 million and $52.6 million, respectively. These increases
were offset by the following: an increase of $362.6 million in borrowings under
mortgage loans; a decrease of $23.5 million in repayments under the credit
facility; a $4.7 million increase in restricted cash; a decrease of $18.1
million in unit issuance costs; and an increase of $1.8 million in option
exercise proceeds.

     The ratio of earnings to fixed charges and dividends on preferred units
increased to 2.84 at December 31, 1999 from 2.06 at December 31, 1998, due
mainly to the net gain on real estate assets during 1999.

     EQUITY TRANSACTIONS

     On January 20, 1998, Cornerstone converted its corporate structure into an
umbrella limited partnership REIT, which is commonly referred to as an UPREIT.
Under the UPREIT structure, Cornerstone assigned substantially all of its assets
to Cornerstone Partnership in exchange for 3,030,303 preferred units and
82,634,231 common units.

     On February 6, 1998, Cornerstone completed a secondary public offering of
14,375,000 shares of common stock at $18.25 per share. The shares were placed in
the U.S. through a syndicate of seven investment banks led by Merrill Lynch &
Co. Cornerstone contributed net proceeds to Cornerstone Partnership of
approximately $247.9 million (approximately $262.3 million in gross proceeds
less an underwriting discount of approximately $13.7 million and expenses of
approximately $0.7 million) in exchange for a corresponding number of units. The
net proceeds were used to repay outstanding borrowings under the revolving
credit facility and for working capital purposes.

     On February 27, 1998, through a dividend reinvestment plan, Cornerstone
received proceeds of approximately $2.0 million and issued an additional 109,007
shares of common stock to stockholders. The net proceeds were contributed to
Cornerstone Partnership in exchange for a corresponding number of units.

     On April 28, 1998, Cornerstone issued 3,428,571 shares of Common Stock to
the Prudential Insurance Company of America, or Prudential, and Cornerstone
Partnership issued 1,657,426 units to certain other persons as partial
consideration for the acquisition of One Memorial Drive. Such securities were
not registered under the Securities Act of 1933, as amended, and were issued in
an exempt transaction pursuant to section 4(2) of the Securities Act.
Cornerstone has filed a registration statement on Form S-3 to register under the
Securities Act the resale by Prudential of such shares of common stock. In
connection with the acquisition, Cornerstone Partnership issued 3,428,571 units
to Cornerstone in exchange for the corresponding real estate investment.

     On May 20, 1998, Cornerstone increased the number of authorized preferred
stock from 15,000,000 shares to 65,000,000 shares and, as a result, Cornerstone
Partnership increased the number of authorized preferred units from 15,000,000
units to 65,000,000 units.

                                       115
<PAGE>   128

     On May 29, 1998, through a dividend reinvestment plan, Cornerstone received
proceeds of approximately $1.8 million and issued an additional 98,487 shares of
common stock to stockholders. The net proceeds were contributed to Cornerstone
Partnership in exchange for a corresponding number of units.

     On June 3, 1998, Cornerstone Partnership issued a total of 1,665,663 units
to certain persons in connection with the acquisition of 201 California Street
and the Wilshire Palisades building. Such securities were not registered under
the Securities Act and were issued in an exempt transaction pursuant to section
4(2) of the Securities Act.

     On August 31, 1998, through a dividend reinvestment plan, Cornerstone
received proceeds of approximately $1.5 million and issued an additional 94,610
shares of common stock to stockholders. The net proceeds were contributed to
Cornerstone Partnership in exchange for a corresponding number of units.

     On November 30, 1998, through a dividend reinvestment plan, Cornerstone
received proceeds of approximately $1.5 million and issued an additional 95,300
shares of common stock to stockholders. The net proceeds were contributed to
Cornerstone Partnership in exchange for a corresponding number of units.

     On December 16, 1998, as part of the consideration paid by Cornerstone
Partnership in connection with the Wilson acquisition, Cornerstone issued
14,884,417 shares of common stock and Cornerstone Partnership issued 16,187,724
units to the former owners of WW&A and the Wilson properties. Such securities
were not registered under the Securities Act and were offered and sold in a
private offering pursuant to section 4(2) of the Securities Act and Regulation D
promulgated thereunder. Cornerstone has filed a registration statement on Form
S-3 to register under the Securities Act the resale by the holders thereof of
the 14,884,417 shares of common stock issued in connection with the Wilson
acquisition and 16,187,724 shares of common stock issuable upon redemption of
the Cornerstone Partnership units issued in connection with the Wilson
acquisition. In connection with the acquisition, Cornerstone Partnership issued
14,884,417 units to Cornerstone in exchange for the corresponding investment.

     On December 16, 1998, in connection with the Wilson acquisition,
Cornerstone issued 11,594,203 shares of common stock to PGGM. Such shares were
not registered under the Securities Act and were offered and sold to PGGM in a
private offering pursuant to section 4(2) of the Securities Act. The proceeds
were contributed to Cornerstone Partnership in exchange for a corresponding
number of units.

     On May 12, 1999, Cornerstone received proceeds of approximately $1.8
million and issued an additional 127,000 shares of common stock due to the
exercise of certain stock options. The proceeds were contributed to Cornerstone
Partnership in exchange for a corresponding number of units.

     On May 28, 1999, through a dividend reinvestment plan, Cornerstone received
proceeds of approximately $1.2 million and issued an additional 76,603 shares of
common stock. The net proceeds were contributed to Cornerstone Partnership in
exchange for a corresponding number of units.

     On July 30, 1999, as a result of the redemption of Cornerstone Partnership
units on a one-for-one basis, Cornerstone issued an additional 562,588 shares of
Common stock.

     On August 3, 1999, as a result of the redemption of Cornerstone Partnership
units on a one-for-one basis, Cornerstone issued an additional 562,587 shares of
common stock.

     On August 17, 1999, Cornerstone reacquired 10,833 shares of restricted
common stock as a result of the forfeiture of these shares by an employee of
Cornerstone.

     On August 31, 1999, through a dividend reinvestment plan, Cornerstone
received proceeds of approximately $1.1 million and issued an additional 70,974
shares of common stock. The net proceeds were contributed to Cornerstone
Partnership in exchange for a corresponding number of units.

     During December 1999, Cornerstone repurchased 347,400 shares of its
outstanding common stock for an aggregate cost of approximately $4.9 million
through its repurchase program. Cornerstone Partnership redeemed a corresponding
number of units held by Cornerstone and contributed the proceeds to Cornerstone
to effect the repurchase.

                                       116
<PAGE>   129

     FUNDS FROM OPERATIONS

     Cornerstone Partnership calculates funds from operations, or FFO, based
upon guidance from the National Association of Real Estate Investment Trusts, or
NAREIT. FFO is defined as net income or loss (computed in accordance with GAAP),
excluding gains or losses from debt restructuring and sales of properties, plus
real estate related depreciation and amortization and after adjustments for
unconsolidated joint ventures.

     Industry analysts generally consider FFO to be an appropriate measure of
performance of a REIT. FFO does not represent cash generated from operating
activities in accordance with generally accepted accounting principles, or GAAP,
and, therefore, should not be considered a substitute for net income as a
measure of performance or a substitute for cash flow from operations as a
measure of liquidity calculated in accordance with GAAP.

     Cornerstone Partnership believes that FFO is helpful to investors as a
measure of the performance of an equity REIT because, along with cash flows from
operating activities, financing activities and investing activities, it provides
investors an understanding of the ability of Cornerstone Partnership to generate
earnings from its recurring operations, after the payment of all administrative
costs and interest expense. For cash flows from operating, financing, and
investing activities in accordance with GAAP. See the Consolidated Statements of
Cash Flows included in the Cornerstone Historical Consolidated Financial
Statements on page F-24.

     Included in FFO for 1999 and 1998, is approximately $25.3 million and $14.5
million, respectively, for free and deferred rental income (after adjustment for
minority interest).

     The table below sets forth the adjustments which were made to the net
income of Cornerstone Partnership in the calculation of FFO for the last two
years (amounts in thousands):

                           FUNDS FROM OPERATIONS (1)

<TABLE>
<CAPTION>
                                                                1999         1998
                                                              ---------    --------
<S>                                                           <C>          <C>
NET INCOME:.................................................  $ 265,249    $ 82,024
  NAREIT adjustments:
  Depreciation and amortization (2).........................     96,726      57,031
  Minority adjustments......................................     (2,686)     (2,022)
  Unconsolidated depreciation (3)...........................      1,507       4,054
  Cumulative effect of a change in accounting principle.....        630          --
  (Gain) loss on sale of assets.............................   (131,034)        173
  Extraordinary loss........................................     10,787       4,303
OTHER ADJUSTMENTS:
  Amortization on rent notes................................         --       1,494
  Severance payments........................................        861         478
                                                              ---------    --------
FUNDS FROM OPERATIONS.......................................    242,040     147,535
                                                              =========    ========
</TABLE>

- ---------------
(1) Although Cornerstone Partnership believes that this table is a full and fair
    presentation of Cornerstone Partnership's FFO, similarly captioned items may
    be defined differently by other REITs, in which case direct comparisons may
    not be possible.

(2) The depreciation and amortization adjustment does not include amortization
    of deferred financing costs and depreciation of non-real estate assets in
    accordance with guidance from NAREIT. For the years ended December 31, 1999
    and 1998, depreciation and amortization includes approximately $4.0 million
    and approximately $0.2 million, respectively, of amortization relating to
    the intangible management and development company assets that were acquired
    as part of the Wilson acquisition.

                                       117
<PAGE>   130

(3) For the years ended December 31, 1999 and 1998, the unconsolidated
    depreciation adjustment includes approximately $0.7 million and $0.2
    million, respectively, of amortization relating to the intangible management
    and development company assets that were acquired as part of the Wilson
    acquisition.

     The increase in FFO from 1998 to 1999 of approximately $94.5 million is
primarily due to the full year of operations of the 69 properties acquired as
part of the Wilson acquisition (eleven of these assets have since been sold), as
well as the four additional properties acquired during 1998.

     MORTGAGE INDEBTEDNESS

     On January 28, 1998, Cornerstone Partnership entered into an $80.0 million
first mortgage on Corporate 500 Centre with Bankers Trust Company. The loan
bears interest at a rate of LIBOR plus 1.0% and matures in July 2002.
Cornerstone Partnership had entered into a $80.0 million interest rate swap to
protect it from interest rate fluctuations that could have affected its floating
rate debt on Corporate 500 Centre. The swap effectively fixed the interest rate
on the $80.0 million loan at 6.63%. This agreement was terminated in August 1998
at no cost to Cornerstone Partnership. On October 9, 1998, Cornerstone
Partnership completed the refinancing of the $80.0 million mortgage on Corporate
500 Centre with Teachers Insurance and Annuity Association. As a result of the
refinancing, the principal balance was increased to $90.0 million, the term of
the loan was extended from 4.5 years to 10 years and the interest rate was
increased by three basis points to 6.66%.

     On June 3, 1998, Cornerstone Partnership assumed the mortgage on 201
California Street in San Francisco, California. The loan required amortization
based on a 30-year schedule and bore interest at a rate of 6.9%. This mortgage
was restructured as part of the Northwestern Mutual Life Insurance Company
restructuring on October 6, 1999.

     On June 3, 1998, Cornerstone Partnership assumed the mortgage on Wilshire
Palisades in Santa Monica, California. The loan requires amortization based on a
22-year schedule and bears interest at a rate of 8.04%. While the face amount of
the loan is $28.8 million, and the interest rate is 8.04%, Cornerstone
Partnership is carrying the debt at $29.0 million, which is the market value of
the loan at the time of the closing, less the amortization of principal and
premium since closing, based upon a market interest rate for similar quality
loans of 6.7%.

     On September 25, 1998, Cornerstone Partnership completed the refinancing of
the $96.1 million mortgage on One Norwest Center with the Connecticut General
Life Insurance Company, or CIGNA, and the Massachusetts Mutual Life Insurance
Company, or Mass Mutual. As a result of the refinancing, the principal balance
was increased to $98.5 million, the term of the loan was extended from three
years to ten years and the interest rate was reduced from 7.50% to 6.90%. In
conjunction with the sale of this property during the fourth quarter of 1999,
the mortgage was assumed by the purchaser at closing.

     On December 16, 1998, Cornerstone Partnership assumed various mortgages
totaling approximately $760.0 million as part of the Wilson acquisition. The
loans have various amortization periods and interest rates. Certain assumed
loans were prepaid subsequent to the closing but prior to year end.

     During June 1999, Cornerstone Partnership restructured approximately $163.0
million of property-related debt with Prudential Insurance Company of America
and Northwestern Mutual Life Insurance Company. The restructuring involved
retiring 17 of the individual property-related debts and creating a single
$180.0 million term loan which is cross-collateralized by six of Cornerstone
Partnership's properties. The loan has a ten-year term and bears interest at
7.26% per annum.

     On October 6, 1999, Cornerstone Partnership restructured approximately
$219.9 million of individual property-related debt with Northwestern Mutual Life
Insurance Company. The restructuring involved retiring the individual
property-related debt and creating a single $275.0 million term loan which is
cross-collateralized by five of the original six properties. The loan has a
ten-year term and bears interest at 7.23%. Upon closing the loan, the lien on 10
Almaden was released and the property was added to Cornerstone Partnership's
unencumbered pool.
                                       118
<PAGE>   131

     On December 15, 1999, through an extension and modification agreement, the
maturity date of the $58.0 million variable rate debt held on Seaport Centre was
extended from December 31, 1999 to December 31, 2000. All other terms of the
note remain unchanged.

     OTHER INDEBTEDNESS

     On November 3, 1998, a syndicate of 17 banks led by Deutsche Bank, The
Chase Manhattan Bank and Bank of America provided Cornerstone Partnership with a
$550.0 million line of credit for acquisitions and general working capital
purposes, which we refer to as the revolving credit facility. The facility is
also available for the issuance of letters of credit. The interest rate on the
revolving credit facility depends on Cornerstone Partnership's ratio of total
debt to total asset value (as defined) at the time of borrowing and will be at a
spread of 1.10% to 1.40% over the applicable LIBOR or Prime Rate at the
borrower's option. The letters of credit will be priced at the applicable
Eurodollar credit spread. The revolving credit facility expires on November 3,
2001. As of December 31, 1999, $329.0 million of the facility was outstanding at
a rate of approximately 8.0%. Of this amount, approximately $250.0 million is
fixed with interest rate swaps, which effectively fix the rate at 6.47%.
Beginning January 2000, the rate will be reduced to 5.41% through the expiration
of the swaps in December 2000. These swaps are considered hedges for federal
income tax purposes. During 1999, the revolving credit facility was amended to
allow Cornerstone Partnership to temporarily increase its leverage from 55.0% to
60.0% for a short period, which has since expired. The amendment also increased
Cornerstone Partnership's ability to enter into mortgage debt by decreasing the
required ratio of total property asset value (as defined) to secured
indebtedness from 2.5 to 1.00 to 2.22 to 1.00.

     Cornerstone Partnership holds debt instruments that are sensitive to
changes in interest rates. The maturity, weighted average interest rates and
fair values are presented in the Cornerstone Partnership Historical Consolidated
Financial Statements on pages F-36 and F-43.

     In the normal course of business, Cornerstone Partnership also faces risks
that are either non-financial or non-qualitative. Such risks principally include
credit risks and legal risks and are not included in the above discussion.

     LIQUIDITY

     At December 31, 1999, Cornerstone Partnership had approximately $19.7
million in cash and cash equivalents and approximately $222.0 million in
restricted cash. Restricted cash includes prepaid rents and security deposits
for some of Cornerstone Partnership's office properties and escrow and reserve
funds for real estate taxes, property insurance, capital improvements, tenant
improvements and leasing costs. These funds were established pursuant to certain
mortgage and construction financing arrangements. Restricted cash also includes
the proceeds from the sale of certain properties during 1999 totaling
approximately $211.5 million which are restricted pursuant to the terms of
section 1031 of the Internal Revenue Code.

     At December 31, 1999, Cornerstone Partnership also had $221.0 million
available under its revolving credit facility for general corporate purposes. In
addition, Cornerstone Partnership anticipates it will receive distributions from
its real estate partnerships, rental income from its fee owned properties and
interest income from its mortgages on a monthly basis that will cover normal
operating expenses and pay distributions to its stockholders and unitholders.
Based upon its cash reserves and other sources of funds, including its $550.0
million revolving credit facility, management believes Cornerstone Partnership
has sufficient liquidity to meet its cash requirements for the remainder of
2000.

OTHER MATTERS

     GENERAL

     Cornerstone Partnership is not aware of any environmental issues at any of
its properties that would have a material adverse impact on Cornerstone
Partnership's operating results or financial condition. Cornerstone Partnership
believes it has sufficient insurance coverage at each of its properties,
including

                                       119
<PAGE>   132

earthquake insurance where necessary. A majority of Cornerstone Partnership's
leases with the majority of its tenants require the tenants to pay most
operating expenses and increases in common area maintenance expenses, which
reduces Cornerstone Partnership's exposure to increases in costs and operating
expenses resulting from inflation.

     CONCENTRATION OF RISK

     Approximately 5.8 million of Cornerstone Partnership's 18 million rentable
square feet is located in the San Francisco metropolitan market, accounting for
approximately 29% of Cornerstone Partnership's total assets at December 31,
1999. In addition, five of Cornerstone Partnership's 83 office properties are
located in the Downtown Boston market, accounting for approximately 19.4% of
Cornerstone Partnership's office and parking revenues for the year ended
December 31, 1999. This concentration of assets makes Cornerstone Partnership
particularly vulnerable to adverse changes in economic conditions in the San
Francisco and Boston metropolitan areas. A significant decline in these economic
conditions could have a material adverse effect on Cornerstone Partnership.

     Norwest Corporation and its subsidiary, Norwest Bank Denver N.A., tenants
of Cornerstone Partnership, provided approximately 6.2% and 10.0% of office and
parking rental income for the years ended December 31, 1999 and 1998,
respectively. Included in deferred tenant receivables is approximately $34.8
million and $33.9 million due from Norwest Corporation at December 31, 1999 and
1998, respectively. As a result of the sale of Cornerstone Partnership's
property located in Denver during the fourth quarter of 1999, the concentration
of revenue received from this tenant will be significantly reduced.

     RECENTLY ISSUED ACCOUNTING STANDARDS

     During the first quarter of 1999, Cornerstone Partnership adopted Statement
of Financial Accounting Standards No. 133, "Accounting for Derivative
Instruments and Hedging Activities," or SFAS 133. SFAS 133 requires that all
derivative instruments be recorded on the balance sheet at their fair value.
Changes in the fair value of derivatives are recorded each period in current
earnings or other comprehensive income, depending on whether a derivative is
designated as part of a hedge transaction and, if it is, the type of hedge
transaction.

     During the first quarter of 1999, Cornerstone Partnership also adopted
Statement of Position 98-5, "Reporting on the Costs of Start-Up Activities," or
SOP 98-5. SOP 98-5 requires that certain costs incurred in conjunction with
start-up and organizational activities be expensed. Pursuant to the requirements
of SOP 98-5, Cornerstone Partnership has written off all unamortized
organizational costs and has recorded a cumulative effect of a change in
accounting principle of $630,044.

     In addition, during the first quarter of 1999, Cornerstone Partnership
adopted Statement of Position 98-1, "Accounting for the Costs of Computer
Software Developed or Obtained for Internal Use," or SOP 98-1. SOP 98-1 provides
guidance on whether the costs of computer software developed or obtained for
internal use should be capitalized or expensed. The adoption of SOP 98-1 did not
have a significant effect on Cornerstone Partnership's financial statements.

     YEAR 2000 COMPLIANCE

     Cornerstone Partnership previously recognized the material nature of the
business issues surrounding computer processing of dates into and beyond the
Year 2000 and began taking corrective action. Cornerstone Partnership's efforts
included: (a) assessment of compliance of information systems at the corporate
offices in New York, Atlanta and San Mateo; (b) assessment of compliance of
information and real estate operating systems at the property sites; and (c)
assessment of compliance of significant service providers including third party
managers and the buildings they manage, vendors and customers, which we refer to
as External Agents. The plan covered the following major tasks: (a) inventory of
all systems; (b) analysis of inventory including assessment of risk; (c)
verification of compliance of inventory with vendors; (d) testing of critical
equipment and processes; and (e) replacement or modification of systems.
Management believes Cornerstone Partnership has completed all of the activities
within its control to
                                       120
<PAGE>   133

ensure that Cornerstone Partnership's systems are Year 2000 compliant and
Cornerstone Partnership has experienced no interruptions to normal operations
due to the start of the Year 2000.

     Cornerstone Partnership's total historical Year 2000 readiness costs were
immaterial to Cornerstone Partnership's financial condition. The costs incurred
in the current fiscal year consisted of recurring system upgrades and
replacements, immaterial internal staff costs and other expenses such as
telephone and mailing costs. Cornerstone Partnership does not anticipate
incurring any additional material costs to address Year 2000 issues.

     As of March 22, 2000, Cornerstone Partnership has not experienced any
material disruptions of its internal computer systems or software applications,
and has not experienced any problems with the computer systems or software
applications of its External Agents. Cornerstone Partnership will continue to
monitor these External Agents to determine the impact, if any, on the business
of Cornerstone Partnership and the actions Cornerstone Partnership must take, if
any, in the event of non-compliance by any of these External Agents. Based upon
Cornerstone Partnership's assessment of compliance by External Agents, there
appears to be no material business risk posed by any such noncompliance.
Moreover, Cornerstone Partnership generally believes that the vendors that
supply products to Cornerstone Partnership are responsible for the products'
Year 2000 functionality.

     Although Cornerstone Partnership's Year 2000 rollover did not present any
material business disruption, there are some remaining Year 2000-related risks,
including risks due to the fact that the Year 2000 is a leap year. These risks
include potential product supply issues and other non-operational issues.
Management believes that appropriate action has been taken to address these
remaining Year 2000 issues and contingency plans are in place to minimize the
financial impact to Cornerstone Partnership. Management, however, cannot be
certain that Year 2000 issues will not have a material adverse impact on
Cornerstone Partnership, since the evaluation process is not yet complete and it
is early in the Year 2000.

     DEVELOPMENT PROJECT

     In April 1998, Cornerstone Partnership entered into a contract to acquire
from the developer the 928,857 square-foot Piper Jaffray building under
construction in Minneapolis. In November 1999, this contract was amended in
connection with a 350,000 square-foot expansion lease with a major tenant of the
building. The contract was amended to provide for a purchase price equal to the
costs incurred in construction and development plus a fixed amount to the
developer plus an additional amount based on the leasing of the building. In
addition, at Cornerstone Partnership's election, the closing of the acquisition
may occur prior to the completion of the building, but the developer will remain
obligated to complete the project. Through December 31, 1999, approximately
$109.4 million has been spent on the construction. The project is scheduled to
be completed in the year 2000 and is approximately 75.0% pre-leased.

SUBSEQUENT EVENTS

     On January 20, 2000, Cornerstone and Cornerstone Partnership declared a
distribution of $0.31 per share and per unit, respectively, paid on February 29,
2000, to common stockholders and unitholders, respectively, of record as of
January 31, 2000.

     On January 21, 2000, Cornerstone Partnership purchased 400 Capitol Mall in
Sacramento, California. This property contains approximately 502,000 rentable
square feet. The total purchase price for the property was approximately $130.0
million, consisting of approximately $128.0 million in cash which were section
1031 exchange funds from the sale of One Norwest Center in Denver, Colorado, and
approximately $2.0 million of which was paid in Cornerstone Partnership units
valued at $17.25 per unit.

     On February 11, 2000, Cornerstone and Cornerstone Partnership announced
that it had entered into the merger agreement, which provides for the REIT
merger and the partnership merger.

     On March 8, 2000, as provided in the merger agreement with Equity Office,
the Board of Directors declared a distribution of $0.20 per share and unit,
respectively, payable on April 14, 2000, to common stockholders and unitholders,
respectively, of record as of March 31, 2000. This distribution was declared
                                       121
<PAGE>   134

to make Cornerstone's and Cornerstone Partnership's distribution schedule
consistent with that of Equity Office pending the merger. Thereafter, it is
anticipated that Cornerstone's and Cornerstone Partnership's distributions will
be paid as of the end of each quarter until the completion of the mergers.

     On March 8, 2000, 9,200 Cornerstone Partnership units were redeemed for
shares of Cornerstone common stock on a one-for-one basis.

     On March 15, 2000, Cornerstone Partnership sold its interest in a property
located in East Bay, California for gross proceeds of $14,425,000. The property
had been acquired as part of the Wilson acquisition in December 1998.

     On March 23, 2000, Cornerstone Partnership sold its interest in a property
located in East Bay, California for gross proceeds of $12,800,000. The property
had been acquired as part of the Wilson acquisition in December 1998.

QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

     Approximately $1.3 billion of Cornerstone Partnership's long-term debt
bears interest at fixed rates, and therefore the fair value of these instruments
is affected by changes in market interest rates. The following table presents
principal cash flows (dollar amounts in thousands) based upon expected maturity
dates of the debt obligations and the related weighted-average interest rates by
expected maturity dates for the fixed rate debt. The interest rate on the
variable rate debt as of December 31, 1999 ranged from LIBOR plus 1.40% to LIBOR
plus 1.65%.

     Annual rates on advances from the revolving credit facility depend on
Cornerstone Partnership's ratio of total debt to asset value (as defined) at the
time of borrowing and will be at a spread of 1.10% to 1.40% over the applicable
LIBOR or prime rate at Cornerstone Partnership's option. Of the total advances
outstanding under the facility at December 31, 1999, $250.0 million is fixed
with interest rate swaps, which effectively fix the rate at 6.47%. Beginning
January 2000, the rate will be reduced to 5.41% through the expiration of the
swaps in December 2000.

<TABLE>
<CAPTION>
                            2000      2001      2002     2003     2004    THEREAFTER     TOTAL     FAIR VALUE
                           -------   -------   ------   ------   ------   ----------   ---------   ----------
<S>                        <C>       <C>       <C>      <C>      <C>      <C>          <C>         <C>
LONG-TERM DEBT:
  Fixed rate.............   65,000        --   62,661       --   86,517   1,037,809    1,251,987   1,183,491
    Average interest
      rate...............     7.28%       --     6.81%      --     7.33%       7.34%
  Variable rate..........  119,192   329,000   48,160   16,066       --          --      512,418     512,418
INTEREST RATE SWAPS:
  Variable to fixed......  250,000        --       --       --       --          --           --          --
    Average pay rate
      (1)................     5.07%       --       --       --       --          --           --          --
    Average receive rate
      (1)................     6.46%       --       --       --       --          --           --          --
</TABLE>

- ---------------
(1) As of December 31, 1999.

              SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND
             MANAGEMENT OF CORNERSTONE AND CORNERSTONE PARTNERSHIP

     The following table sets forth certain information with respect to the
beneficial ownership of the Cornerstone Partnership units by:

     - each person or entity known by Cornerstone Partnership to be the
       beneficial owner of more than 5% of the outstanding units;

     - each of Cornerstone's directors and executive officers; and

     - all of Cornerstone's directors and executive officers as a group.

                                       122
<PAGE>   135

     Unless otherwise identified, the address of each of the beneficial owners
identified is c/o Cornerstone Properties Inc., Tower 56, 126 East 56th Street,
New York, NY 10022. Except as otherwise indicated, such beneficial owners have
sole voting and investment power with respect to all units owned by them,
subject to community property laws where applicable.

     Percentage of ownership is based on 148,852,333 Cornerstone Partnership
units outstanding on             , 2000. Percentage of ownership also is based
on:

     - 0.7009 EOP Partnership units being issued for each Cornerstone
       Partnership unit;

     - an estimated                EOP Partnership units outstanding following
       the partnership merger; and

     - no redemptions of Cornerstone Partnership units for Cornerstone common
       stock prior to the partnership merger.

<TABLE>
<CAPTION>
                                                       UNITS BENEFICIALLY OWNED
                                                       PRIOR TO THE PARTNERSHIP      PERCENT OF EOP
                                                                MERGER             PARTNERSHIP UNITS
                                                       ------------------------        AFTER THE
NAME                                                      UNITS        PERCENT     PARTNERSHIP MERGER
- ----                                                   ------------    --------    ------------------
<S>                                                    <C>             <C>         <C>
Cornerstone Properties Inc...........................  129,638,245       87.1%
Cecil D. Conlee......................................            0          *
Rodney C. Dimock.....................................            0          *
Blake Eagle..........................................            0          *
Donald G. Fisher.....................................      539,196(1)       *
Randall A. Hack......................................            0          *
Dr. Karl-Ludwig Hermann..............................            0          *
Hans C. Mautner......................................            0          *
Dr. Lutz Mellinger...................................            0          *
John S. Moody........................................            0          *
Craig R. Stapleton...................................            0          *
Michael J. G. Topham.................................            0          *
Dick van den Bos.....................................            0          *
Jan H.W.R. van der Vlist.............................            0          *
William Wilson III...................................    1,182,572(2)       *
John J. Hamilton, III................................      183,655          *
Thomas P. Loftus.....................................            0          *
Kevin P. Mahoney.....................................            0          *
R. Matthew Moran.....................................       31,889(3)       *
Thomas A. Nye........................................            0          *
Stephen J. Pilch.....................................            0          *
A. Robert Paratte....................................        7,771          *
H. Lee Van Boven.....................................       29,770          *
All directors and executive officers as a group (22
  persons)...........................................    1,974,853        1.3%
</TABLE>

- ---------------
(1) Includes:
     - 226,146 units owned jointly with Mr. Fisher's spouse; and
     - 313,050 units deemed beneficially owned by Mr. Fisher as a result of his
       control of DDRWJ Investment Company.

(2) Includes:
     - 22,845 units held by Mr. Wilson as trustee for three trusts for the
       benefit of his children;
     - 639,191 units held directly by Mr. Wilson;
     - 294,630 units deemed beneficially owned by Mr. Wilson as a result of his
       control of Wilson Investment Associates, Ltd.; and

                                       123
<PAGE>   136

     - 225,906 units beneficially owned by Mr. Wilson through a family
       partnership.

       Does not include 3,160,513 units which may be deemed beneficially owned
       by Mr. Wilson as a result of his control of four entities and of which
       Mr. Wilson may be deemed to share voting and dispositive power with other
       executive officers of Cornerstone.

(3) Includes 27,682 units deemed beneficially owned by Mr. Moran as a result of
    his control of Moran Investments LLC.

                                       124
<PAGE>   137

      CORNERSTONE PARTNERSHIP POLICIES WITH RESPECT TO CERTAIN ACTIVITIES

     The following is a discussion of the historical policies of Cornerstone
Partnership with respect to its investments. These policies have been
historically determined by the Cornerstone board of directors and may be amended
or revised from time to time at the discretion of the Cornerstone board without
notice to or a vote of Cornerstone's stockholders or Cornerstone Partnership's
unitholders.

     Investments in Real Estate or Interests in Real Estate. All of
Cornerstone's investment activities are conducted through Cornerstone
Partnership. Cornerstone's investment objectives have been to increase cash flow
and the value of its properties, and to acquire established income-producing
office properties with cash flow growth potential. Additionally, where prudent
and possible, Cornerstone has sought to upgrade its existing properties and any
newly acquired office properties. Cornerstone's business has been focused on
office properties. Where appropriate, and subject to the qualification rules
governing REITs, Cornerstone has sold some of its properties.

     Cornerstone has pursued its investment objectives through the direct and
indirect ownership of properties and through the ownership of interests in other
entities. Cornerstone has focused on properties in major metropolitan markets
and in new markets targeted by its management. Although management of
Cornerstone does not anticipate any future investments due to the mergers, any
newly acquired properties would be located in the United States, but Cornerstone
would not limit its activities to any specific geographic area of the United
States.

     Cornerstone Partnership has also historically participated with other
entities in property ownership through joint ventures or other types of
co-ownership. Equity investments may be subject to existing mortgage financing
and other indebtedness or such financing or indebtedness may have been incurred
in connection with the acquisition of an investment. Any such financing of
indebtedness would have priority over Cornerstone Partnership's equity interest
in such property. Upon consummation of the mergers, EOP Partnership will succeed
to Cornerstone Partnership's interest in its joint venture properties. See
"Business of Cornerstone Partnership -- Ownership and Management of Cornerstone
Partnership Properties" on page 102.

     Investments in Real Estate Mortgages. With the exception of its investment
in Sixty State Street, Cornerstone Partnership has not historically invested in
mortgages on office properties or other similar interests with respect to which
Cornerstone Partnership does not own, either fully or partially, including any
joint venture properties, the property underlying the mortgage. Due to the
mergers, Cornerstone Partnership does not intend to invest in mortgages or deeds
of trust in the future, but if the mergers are not completed, Cornerstone
Partnership may engage in such investments, primarily as a strategy for
acquiring ownership of a property or the economic equivalent thereof, subject to
the investment restrictions applicable to REITs. In addition, if the mergers are
not completed, Cornerstone Partnership may invest in mortgage-related securities
and/or may seek to issue securities representing interests in such mortgage-
related securities as a method of raising additional funds.

     Investments in Securities of or Interests in Persons Primarily Engaged in
Real Estate Activities and Other Securities. Although Cornerstone Partnership
has not historically made and has no current intention, if the mergers are not
completed, to make such investments, it may legally invest in securities of
entities engaged in real estate activities or securities of other issuers,
including for the purpose of exercising control over such entities, subject to
the gross income and asset tests necessary for qualification of Cornerstone as a
REIT. If the mergers are not completed, Cornerstone Partnership may in the
future acquire all or substantially all of the securities or assets of other
REITs or similar entities where such investments would be consistent with
Cornerstone Partnership's investment policies. In any event, Cornerstone
Partnership does not intend that any investment it might make in securities,
absent the completion of the mergers, to require it or Cornerstone Partnership
to register as an "investment company" under the Investment Company Act of 1940.

                                       125
<PAGE>   138

                  DESCRIPTION OF EOP PARTNERSHIP CLASS A UNITS

     The following summary of the terms of the EOP Partnership class A units is
qualified in its entirety by reference to the partnership agreement of EOP
Partnership. For information on how to obtain a copy of the partnership
agreement of EOP Partnership, see "Where You Can Find More Information" on page
163.

CAPITALIZATION

     As of the date of this consent solicitation/information
statement/prospectus, EOP Partnership has the following units issued and
outstanding:

     -      class A units;

     -      class B units;

     -      series A preferred units;

     -      series B preferred units; and

     -      series C preferred units.

     Equity Office owns all of the series A, series B and series C preferred
units and      of the class A units. Before the partnership merger, Equity
Office will take all necessary actions to cause EOP Partnership to issue
3,030,303 series D preferred units. EOP Partnership will issue the series D
preferred units in the partnership merger in exchange for the outstanding
Cornerstone Partnership class A preferred units. All of the EOP Partnership
series D preferred units to be issued in the partnership merger will be issued
to Cornerstone and will be acquired by Equity Office in the REIT merger.
Following the REIT merger and the elimination of the Cornerstone cumulative
convertible preferred stock in exchange for cash, the EOP Partnership series D
preferred units will be converted to      EOP Partnership class A units.

ISSUANCE OF ADDITIONAL PARTNERSHIP INTERESTS

     Equity Office is authorized to cause EOP Partnership to issue additional
partnership units or interests to its partners, including Equity Office and its
affiliates, or other persons. These units may be issued in one or more classes
or in one or more series of any class, with designations, preferences and
relative, participating, optional or other special rights, powers and duties,
including rights, powers and duties senior to those of the class A common units,
as determined by Equity Office in its sole and absolute discretion without the
approval of any limited partner, subject to limitations described below.

     No partnership unit or interest may be issued to Equity Office as general
partner or limited partner unless:

     - EOP Partnership issues the units or other partnership interests in
       connection with the grant, award or issuance of shares or other equity
       interests in Equity Office having designations, preferences and other
       rights so that the economic interests attributable to the newly issued
       shares or other equity interests are substantially similar to the
       designations, preferences and other rights of the EOP Partnership units
       or other partnership interests issued to Equity Office, and Equity Office
       contributes to EOP Partnership the proceeds from the issuance of the
       shares or other equity interests received by Equity Office; or

     - EOP Partnership issues the additional EOP Partnership units or other
       partnership interests to all partners holding EOP Partnership units or
       other partnership interests in the same class or series in proportion to
       their respective percentage interests in that class or series.

     At the election of Equity Office, in its sole and absolute discretion, EOP
Partnership may issue either class A units or class B units to newly admitted
partners. The major difference between class A units and class B units is that
the class A units receive a full distribution of any cash distributed by EOP
Partnership with respect to its units, without any proration to take into
account the number of days that the class A

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units were outstanding, while distributions to the class B units are prorated
based upon the number of days in the applicable distribution period that the
class B units were outstanding. Any EOP Partnership unit that is not
specifically designated by Equity Office as being of a particular class will be
deemed to be a class A unit. In the partnership merger, EOP Partnership class A
units will be issued in exchange for Cornerstone Partnership class A common
units and EOP Partnership series D preferred units will be issued in exchange
for Cornerstone Partnership class A preferred units.

CAPITAL CONTRIBUTIONS

     Partners of EOP Partnership are not required to make additional capital
contributions to EOP Partnership unless they have entered into a separate
agreement, generally referred to as a deficit restoration obligation, that
requires additional contributions upon liquidation of EOP Partnership. However,
Equity Office generally is required to contribute net proceeds of any sale of
equity interests in Equity Office to EOP Partnership in exchange for additional
partnership units, as described above. Limited partners of Cornerstone
Partnership receiving EOP Partnership units in the partnership merger will not
be required to pay to EOP Partnership any deficit or negative balance which may
exist in their capital accounts unless in connection with or subsequent to the
partnership merger they elect to enter into an express agreement with EOP
Partnership undertaking a deficit restoration obligation.

DISTRIBUTIONS

     The partnership agreement of EOP Partnership requires the distribution, on
a quarterly or shorter basis, of available cash. Available cash is the net
operating cash flow plus any reduction in reserves and minus interest and
principal payments on debt, capital expenditures, any additions to reserves and
other adjustments, as determined by Equity Office in its sole discretion. EOP
Partnership makes distributions to all partners who are partners on the record
date for the distribution in the following order:

     - first, to each partner, including Equity Office, who holds a partnership
       interest of a class or series that is entitled to a preference according
       to the rights of that class or series of partnership interest; and

     - second, to the extent that there is available cash available after
       payment of any preferences, to the partners who hold a partnership
       interest that is not entitled to a preference in distribution, including
       class A units and class B units, pro rata to each class or series and,
       within each class or series, in proportion to the partner's percentage
       share of that class or series.

     Unless otherwise specifically agreed to by Equity Office in the partnership
agreement of EOP Partnership or an agreement at the time a new class or series
is created, no partnership interest will be entitled to a distribution in
preference to any other. As a general rule, distributions payable with respect
to any class A units that were not outstanding during the entire quarterly or
shorter period on which the distribution is based will not be prorated based on
the portion of the period that these units were outstanding, but distributions
paid with respect to class B units will be prorated. An EOP Partnership partner
will not in any event receive a distribution of available cash with respect to a
partnership unit if the partner is entitled to receive a distribution out of
that same available cash with respect to an Equity Office share for which that
partnership unit has been exchanged or redeemed.

     Equity Office will make reasonable efforts, as determined by it in its sole
and absolute discretion and consistent with Equity Office's qualification as a
REIT, to distribute available cash:

     - to the limited partners so as to preclude the distribution from being
       treated as part of a disguised sale for federal tax purposes; and

     - to all units so that the amount distributed to Equity Office is
       sufficient to enable Equity Office to pay shareholder dividends that
       will:

      -- satisfy the requirements for qualifying or re-electing as a REIT; and

      -- avoid any federal income or excise tax liability for Equity Office.
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     If Equity Office is not publicly traded, EOP Partnership will make cash
distributions with respect to class A units at least annually for each taxable
year of EOP Partnership beginning before July 11, 2012 in an aggregate amount
that reflects at least 95% of EOP Partnership's taxable income for that year
allocable to the class A units.

PREEMPTIVE RIGHTS

     Except to the extent expressly granted by EOP Partnership in an agreement
other than the partnership agreement of EOP Partnership, no person or entity,
including any partner of EOP Partnership, has any preemptive, preferential or
other similar right with respect to:

     - additional capital contributions or loans to EOP Partnership; or

     - the issuance or sale of any EOP Partnership units or other partnership
       interests of EOP Partnership.

CONVERSION; REDEMPTION

     Each EOP Partnership class B unit will be converted automatically into an
EOP Partnership class A unit on the day immediately following the record date
for the distribution period during which the EOP Partnership class B unit was
issued.

     In the absence of the limitations described below, each holder of class A
units other than Equity Office and some of its affiliates has a unit redemption
right which is a right to require the redemption of its EOP Partnership class A
units by EOP Partnership. As a general rule, a limited partner may exercise the
redemption right at any time beginning on the first anniversary of the issuance
of the partnership units held by it. Specific investors described in the
partnership agreement of EOP Partnership, however, only may exercise the
redemption right on the second anniversary of the issuance of EOP Partnership
units to them. Equity Office may agree to a shorter waiting period, or no
waiting period, on the exercise of the unit redemption right. Cornerstone
Partnership limited partners who receive EOP Partnership class A units in the
partnership merger will be permitted to exercise the unit redemption right at
any time following the partnership merger.

     In addition, each limited partner may exercise its unit redemption right,
regardless of the length of time it has held its EOP Partnership units, during
the period commencing on the date Equity Office has given the limited partners
notice of its intention to make an extraordinary distribution of cash or
property to its shareholders or effect a merger, a sale of all or substantially
all of its assets, or any other similar extraordinary transaction, which notice
must be given at least 20 business days prior to the record date for determining
shareholders eligible to receive the distribution or to vote upon the approval
of the merger, sale or other extraordinary transaction, and ending on such
record date. Equity Office, in its sole discretion, may shorten the required
notice period of not less than twenty business days prior to the record date to
determine the shareholders eligible to vote upon a merger transaction (but not
any of the other covered transactions) by up to ten business days (thereby
continuing to afford the holders of units the opportunity to redeem units on or
prior to the record date for the shareholder vote on the merger transaction) so
long as (a) Equity Office will be the surviving entity in such merger
transaction, (b) immediately following the merger transaction, persons who held
voting securities of Equity Office immediately prior to such merger transaction
will hold, solely by reason of the ownership of voting securities of Equity
Office immediately prior to the merger transaction, voting securities of Equity
Office representing not less than 51% of the total combined voting power of all
outstanding voting securities of Equity Office after such merger, and (c) in the
event that in connection with such merger transaction EOP Partnership will merge
with another entity, EOP Partnership will be the surviving entity in such
merger. If no record date as described is applicable, the date shall be at least
20 business days before the consummation of the merger, sale or other
extraordinary transaction.

     A limited partner may exercise its unit redemption right by giving written
notice to EOP Partnership and Equity Office. The EOP Partnership units specified
in the notice shall be redeemed on the 10th

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business day following the date Equity Office received the redemption notice or,
in the case of the exercise of a unit redemption right in connection with an
extraordinary transaction, the date EOP Partnership and Equity Office received
the redemption notice.

     A notice of redemption delivered to EOP Partnership by the limited partner
exercising the right will exercise the redemption right. A limited partner may
not exercise the redemption right for fewer than 1,000 partnership units, or if
the limited partner holds fewer than 1,000 partnership units, all of the
partnership units held by that limited partner. The redeeming partner will have
no right to receive any distributions paid on or after the redemption date with
respect to those partnership units redeemed.

     Unless Equity Office elects to assume and perform EOP Partnership's
obligation with respect to the unit redemption right, as described below, a
limited partner which exercises its unit redemption right will receive cash from
EOP Partnership in an amount equal to the market value of the EOP Partnership
units to be redeemed. The market value of an EOP Partnership unit for this
purpose will be equal to the average of the closing trading price of an Equity
Office common share on the NYSE for the ten trading days before the day on which
the redemption notice was given.

     Instead of EOP Partnership acquiring the units being redeemed for cash,
Equity Office has the right to elect to acquire on the redemption date the EOP
Partnership units directly from a limited partner exercising the unit redemption
right in exchange for either cash in the amount specified above or a number of
Equity Office common shares equal to the number of EOP Partnership units offered
for redemption, adjusted as specified in the partnership agreement of EOP
Partnership to take into account prior share dividends or any subdivisions or
combinations of Equity Office common shares. No redemption or exchange can occur
if delivery of common shares by Equity Office would be prohibited either under
the provisions of Equity Office's Declaration of Trust or under applicable
federal or state securities laws, regardless of whether Equity Office would in
fact elect to assume and satisfy the unit redemption right. Equity Office will
at all times reserve and keep available out of its authorized but unissued
Equity Office common shares, solely for the purpose of effecting the issuance of
Equity Office common shares through a unit redemption right, a number of Equity
Office common shares that would be sufficient for the redemption of all
outstanding EOP Partnership units not owned by Equity Office.

     Unless Equity Office exercises its right to purchase the redeeming
partner's EOP Partnership units, as described above, Equity Office has no
obligation to the redeeming partner with respect to the redeeming partner's unit
redemption right. Likewise, if Equity Office exercises this purchase option, EOP
Partnership has no obligation to pay any amount to the redeeming partner with
respect to the unit redemption right. If Equity Office elects to assume and
perform the obligations of EOP Partnership under the unit redemption right, each
of the redeeming partner, EOP Partnership and Equity Office will treat this
transaction between Equity Office and the redeeming partner, for federal tax
purposes, as a sale of the redeeming partner's EOP Partnership units to Equity
Office.

     If any Equity Office preferred shares have been called for redemption, a
number of EOP Partnership preferred units equal to the number of Equity Office
preferred shares called for redemption will be redeemed. The redemption shall
occur at a time and in a manner that allows the redemption of Equity Office
preferred shares to be completed in a timely fashion to comply with the
applicable requirements related to the share redemption.

     All EOP Partnership units delivered for redemption must be delivered to EOP
free and clear of all liens.

MANAGEMENT

     Except as otherwise expressly provided in the partnership agreement of EOP
Partnership, the business and affairs of EOP Partnership are managed by Equity
Office, which has the exclusive right and full authority and responsibility to
manage and operate the partnership's business. Limited partners do not have any
right to participate in or exercise control or management power over the
business and affairs of EOP Partnership or the power to sign documents for or
otherwise bind EOP Partnership. Equity Office has full

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power and authority to do all things it deems necessary or desirable to conduct
the business of EOP Partnership. However, the consent of the limited partners to
some limited matters is necessary in limited circumstances. In particular,
Equity Office is under no obligation to consider the tax consequences to limited
partners when making decisions for the benefit of EOP Partnership. The limited
partners have no power to remove Equity Office as general partner. Equity
Office, however, may not take any action that is contrary to an express
limitation or prohibition in the partnership agreement of EOP Partnership
without the written consent of:

     - all partners adversely affected; or

     - the lower percentage of the limited partners as may be specifically
       provided for in the partnership agreement of EOP Partnership.

SALE OF SUBSTANTIALLY ALL OF THE PARTNERSHIP ASSETS

     A sale of all or substantially all of the assets of EOP Partnership in a
single transaction or a series of related transactions, including by way of a
merger, consolidation or other combination of EOP Partnership with another
entity, will require the following:

     - if the transaction is in connection with a similar transaction involving
       Equity Office which has also been approved by a majority of the
       outstanding EOP Partnership units, including EOP Partnership units held
       directly or indirectly by Equity Office, and in connection with which all
       limited partners have the right to receive consideration which, on a per
       unit basis, is equivalent in value to the consideration to be received by
       the shareholders of Equity Office on a per share basis, approval by a
       majority of the outstanding EOP Partnership units, including EOP
       Partnership units held directly or indirectly by Equity Office; or

     - in the case of any other transaction, the approval of a majority of the
       outstanding EOP Partnership units held by persons or entities other than
       Equity Office and some of its affiliates.

TRANSFERS

     Equity Office may not transfer any of its partnership interests, including
any of its limited partnership interests, except in connection with a merger,
consolidation or other combination with or into another person, a sale of all or
substantially all of its assets or any reclassification, recapitalization or
change of its outstanding shares and only if the transaction has been approved
by the consent of the partners holding at least a majority of the then
outstanding EOP Partnership units, including any EOP Partnership units held by
Equity Office and in connection with which all limited partners have the right
to receive consideration which, on a per unit basis, is equivalent in value to
the consideration to be received by the shareholders of Equity Office, on a per
share basis. Equity Office will not withdraw from EOP Partnership except in
connection with a transaction as described in the preceding sentence.

     A limited partner, other than Equity Office, may transfer, with or without
the consent of Equity Office, all or any portion of its partnership interest, or
any of its economic rights as a limited partner, if:

     - the transfer does not violate any federal or state securities laws or
       regulations applicable to EOP Partnership or the EOP Partnership units;
       or

     - the transfer does not change or potentially affect adversely the tax
       status of EOP Partnership.

     In the case of a proposed transfer of units to a lender to EOP Partnership
or any person related to the lender whose loan constitutes a nonrecourse
liability, the transferring partner must obtain the consent of Equity Office.

     No transferee of a limited partnership interest will be admitted as a
limited partner without the consent of Equity Office, which may be given or
withheld in its sole and absolute discretion.

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AMENDMENT OF PARTNERSHIP AGREEMENT

     Amendments to the partnership agreement of EOP Partnership may be proposed
by Equity Office or by limited partners owning at least 25% of the total
partnership interests. Except as described below, the partnership agreement of
EOP Partnership may be amended with the approval of Equity Office and limited
partners holding a majority of the partnership interests held by the limited
partners, including Equity Office. Equity Office has the power, without the
consent of the limited partners, to amend the partnership agreement of EOP
Partnership as may be required:

     - to add to the obligations of the general partner or surrender any right
       or power granted to Equity Office or any affiliate of Equity Office for
       the benefit of the limited partners;

     - to reflect the admission, substitution, termination or withdrawal of
       partners in compliance with the partnership agreement of EOP Partnership;

     - to declare the designations, rights, powers, duties and preferences of
       the holders of any additional partnership interests issued in accordance
       with the authority granted to Equity Office;

     - to reflect a change that does not affect the limited partners in any
       material respect, or to cure any ambiguity, correct or supplement any
       provision in the partnership agreement of EOP Partnership not
       inconsistent with law or with other provisions of the partnership
       agreement of EOP Partnership, or make other changes with respect to
       matters arising under the partnership agreement of EOP Partnership that
       will not be inconsistent with law or with the provisions of the
       partnership agreement of EOP Partnership; and

     - to satisfy any requirements, conditions or guidelines contained in any
       order, directive, opinion, ruling or regulation of a federal, state or
       local law.

     The approval of a majority of the partnership interests held by limited
partners other than Equity Office is necessary to amend provisions regarding,
among other things:

     - restrictions imposed on the issuance of additional EOP Partnership units
       or other partnership interests to Equity Office;

     - distribution requirements with respect to the EOP Partnership class A
       units if Equity Office is not publicly traded;

     - the prohibition against removal of Equity Office by the limited partners;

     - restrictions on Equity Office's power to conduct businesses other than
       owning partnership interests of EOP Partnership;

     - limitations on transactions with affiliates;

     - the liability of Equity Office for monetary damages to EOP Partnership;

     - partnership consent requirements for the sale of substantially all the
       assets of EOP Partnership; or

     - the transfer of partnership interests held by Equity Office, the
       admission and rights of substituted limited partners or the dissolution
       of EOP Partnership.

     Any amendment of the provision of the partnership agreement of EOP
Partnership which allows the voluntary dissolution of EOP Partnership before
December 31, 2046 can be made only with the approval of 90% of the outstanding
partnership interests, including partnership interests held by Equity Office.

     Amendments to the partnership agreement of EOP Partnership that would,
among other things:

     - convert a limited partner's interest into a general partner's interest;

     - modify the limited liability of a limited partner;

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     - alter the interest of a partner in profits or losses, or the right to
       receive any distributions, except as permitted under the partnership
       agreement of EOP Partnership with respect to the admission of new
       partners or the issuance of additional EOP Partnership units; or

     - alter the unit redemption right of the limited partners of EOP
       Partnership,

must be approved by each limited partner that would be adversely affected by the
amendment.

MEETINGS

     Meetings of the partners may be called by Equity Office by written request
by limited partners holding 25% or more of the partnership interests. The call
must state the nature of the business to be transacted. Notice of any meeting is
required to be given to all partners not less than seven days nor more than 30
days before the date of the meeting. Partners may vote in person or by proxy at
the meeting. Whenever the vote or consent of partners is permitted or required
under the partnership agreement of EOP Partnership, this vote or consent may be
given at a meeting of partners. Except as otherwise expressly provided in the
partnership agreement of EOP Partnership, the consent of a majority of the
percentage interests held by limited partners, including limited partnership
interests held by Equity Office, shall control.

     Any action required or permitted to be taken at a meeting of the partners
may be taken without a meeting if a written consent showing the action taken is
signed by a majority of the percentage interests of the partners or another
percentage as required by the partnership agreement of EOP Partnership.

                      COMPARISON OF RIGHTS OF UNITHOLDERS

     At the time of the partnership merger, Cornerstone Partnership unitholders
automatically will become EOP Partnership unitholders and their rights as
partners will be determined by the partnership agreement of EOP Partnership. The
following is a summary of the material differences in the rights of partners of
EOP Partnership and the rights of partners of Cornerstone Partnership. Note that
Equity Office is the general partner of EOP Partnership and Cornerstone is the
general partner of Cornerstone Partnership. As general partners, Equity Office
and Cornerstone have the exclusive right to manage the business and affairs of
EOP Partnership and Cornerstone Partnership, respectively. This summary is not
complete. Therefore, you should refer to the partnership agreements, including
all amendments, of EOP Partnership and Cornerstone Partnership for complete
information.

CAPITALIZATION

     EOP Partnership.  As of the date of this consent solicitation/information
statement/prospectus, EOP Partnership has the following units issued and
outstanding:

     -      class A units;

     -      class B units;

     -      series A preferred units;

     -      series B preferred units; and

     -      series C preferred units.

     Equity Office owns all of the series A, series B and series C preferred
units and      of the class A units. Before the partnership merger, Equity
Office will take all necessary actions to cause EOP Partnership to issue
3,030,303 series D preferred units. EOP Partnership will issue the series D
preferred units in the partnership merger in exchange for the outstanding
Cornerstone Partnership class A preferred units. All of the EOP Partnership
series D preferred units to be issued in the partnership merger will be issued
to Cornerstone and will be acquired by Equity Office in the REIT merger.
Following the REIT

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merger and the elimination of the Cornerstone cumulative convertible preferred
stock in exchange for cash, the EOP Partnership series D preferred units will be
converted to      EOP Partnership class A units.

     Cornerstone Partnership.  As of the date of this consent
solicitation/information statement/prospectus, Cornerstone Partnership has
issued and outstanding 148,852,333 class A common units and 3,030,303 class A
preferred units.

ISSUANCE OF ADDITIONAL PARTNERSHIP INTERESTS

     EOP Partnership.  Equity Office is authorized to cause EOP Partnership to
issue additional partnership units or interests to its partners, including
Equity Office and its affiliates, or other persons. These units may be issued in
one or more classes or in one or more series of any class, with designations,
preferences and relative, participating, optional or other special rights,
powers and duties, including rights, powers and duties senior to those of the
class A common units, as determined by Equity Office in its sole and absolute
discretion without the approval of any limited partner, subject to limitations
described below.

     No partnership unit or interest may be issued to Equity Office as general
partner or limited partner unless:

     - EOP Partnership issues the units or other partnership interests in
       connection with the grant, award or issuance of shares or other equity
       interests in Equity Office having designations, preferences and other
       rights so that the economic interests attributable to the newly issued
       shares or other equity interests are substantially similar to the
       designations, preferences and other rights of the EOP Partnership units
       or other partnership interests issued to Equity Office, and Equity Office
       contributes to EOP Partnership the proceeds from the issuance of the
       shares or other equity interests received by Equity Office; or

     - EOP Partnership issues the additional EOP Partnership units or other
       partnership interests to all partners holding EOP Partnership units or
       other partnership interests in the same class or series in proportion to
       their respective percentage interests in that class or series.

     At the election of Equity Office, in its sole and absolute discretion, EOP
Partnership may issue either class A units or class B units to newly admitted
partners. The major difference between class A units and class B units is that
the class A units receive a full distribution of any cash distributed by EOP
Partnership with respect to its units, without any proration to take into
account the number of days that the class A units were outstanding, while
distributions to the class B units are prorated based upon the number of days in
the applicable distribution period that the class B units were outstanding. Any
EOP Partnership unit that is not specifically designated by Equity Office as
being of a particular class will be deemed to be a class A unit. In the
partnership merger, EOP Partnership class A units will be issued in exchange for
Cornerstone Partnership class A common units and EOP Partnership class D
preferred units will be issued in exchange for Cornerstone Partnership class A
preferred units.

     Cornerstone Partnership.  Cornerstone is authorized to cause Cornerstone
Partnership to issue additional partnership units or interests to its partners,
including Cornerstone and its affiliates, or other persons. These units may be
issued in one or more classes or in one or more series of any class, with
designations, preferences and relative, participating, optional or other special
rights, powers and duties, including rights, powers and duties senior to those
of the Cornerstone Partnership units, as determined by Cornerstone in its sole
and absolute discretion without the approval of any limited partner, subject to
limitations detailed below.

     No partnership unit or interest may be issued to Cornerstone as general
partner or limited partner unless:

     - Cornerstone Partnership issues the units or other partnership interests
       in connection with the grant, award or issuance of shares or other equity
       interests in Cornerstone having designations, preferences and other
       rights so that the economic interests attributable to the newly issued
       shares or other equity interests are substantially similar to the
       designations, preferences and other rights of the

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       additional partnership interests issued to Cornerstone, and Cornerstone
       contributes to Cornerstone Partnership the proceeds from the issuance of
       the shares or other equity interests received by Cornerstone;

     - Cornerstone Partnership issues the additional Cornerstone Partnership
       units or other partnership interests to all partners holding Cornerstone
       Partnership units or other partnership interests in the same class or
       series in proportion to their respective percentage interests in that
       class or series;

     - the additional Cornerstone Partnership units are issued upon the
       conversion or redemption of preferred shares of Cornerstone; or

     - the additional Cornerstone Partnership units are issued upon the
       conversion, redemption or exchange of debt, partnership units or other
       securities issued by Cornerstone or Cornerstone Partnership.

     Unless specifically designated by Cornerstone, any additional Cornerstone
Partnership interest issued will be deemed a Cornerstone Partnership unit.

CAPITAL CONTRIBUTIONS

     EOP Partnership.  Partners of EOP Partnership are not required to make
additional capital contributions to EOP Partnership unless they have entered
into a separate agreement, generally referred to as a deficit restoration
obligation, that requires additional contributions upon liquidation of EOP
Partnership. However, Equity Office generally is required to contribute net
proceeds of any sale of equity interests in Equity Office to EOP Partnership in
exchange for additional partnership units, as described above. Limited partners
of Cornerstone Partnership receiving EOP Partnership units in the partnership
merger will not be required to pay to EOP Partnership any deficit or negative
balance which may exist in their capital accounts unless in connection with or
subsequent to the partnership merger they elect to enter into an express
agreement with EOP Partnership undertaking a deficit restoration obligation.

     Cornerstone Partnership.  Partners are not required to make additional
capital contributions to Cornerstone Partnership unless they have entered into a
separate deficit restoration obligation that requires additional capital
contributions upon liquidation of Cornerstone Partnership. However, Cornerstone
generally is required to contribute to Cornerstone Partnership net proceeds of
any sale of equity interests in Cornerstone.

     As described in "The Merger Agreement -- Tax Related Undertakings of EOP
Partnership -- Deficit Restoration Obligations," limited partners in Cornerstone
Partnership that have entered into a deficit restoration obligation to
Cornerstone Partnership prior to the partnership merger will have the right to
make a similar undertaking to EOP Partnership at the time of the partnership
merger; and former limited partners of Cornerstone Partnership will have a
limited opportunity to make new deficit restoration obligation commitments to
EOP Partnership from time to time following the partnership merger.

DISTRIBUTIONS

     EOP Partnership.  The partnership agreement of EOP Partnership requires the
distribution, on a quarterly or shorter basis, of available cash. Available cash
is the net operating cash flow plus any reduction in reserves and minus interest
and principal payments on debt, capital expenditures, any additions to reserves
and other adjustments, as determined by Equity Office in its sole discretion.
EOP Partnership makes distributions to all partners who are partners on the
record date for the distribution in the following order:

     - first, to each partner, including Equity Office, who holds a partnership
       interest of a class or series that is entitled to a preference according
       to the rights of that class or series of partnership interest; and

     - second, to the extent that there is available cash available after
       payment of any preferences, to the partners who hold a partnership
       interest that is not entitled to a preference in distribution, including
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       class A units and class B units, pro rata to each class or series and,
       within each class or series, in proportion to the partner's percentage
       share of that class or series.

     Unless otherwise specifically agreed to by Equity Office in the partnership
agreement of EOP Partnership or an agreement at the time a new class or series
is created, no partnership interest will be entitled to a distribution in
preference to any other. As a general rule, distributions payable with respect
to any class A units that were not outstanding during the entire quarterly or
shorter period on which the distribution is based will not be prorated based on
the portion of the period that these units were outstanding, but distributions
paid with respect to class B units will be prorated. An EOP Partnership partner
will not in any event receive a distribution of available cash with respect to a
partnership unit if the partner is entitled to receive a distribution out of
that same available cash with respect to an Equity Office share for which that
partnership unit has been exchanged or redeemed.

     Equity Office will make reasonable efforts, as determined by it in its sole
and absolute discretion and consistent with Equity Office's qualification as a
REIT, to distribute available cash:

     - to the limited partners so as to preclude the distribution from being
       treated as part of a disguised sale for federal tax purposes; and

     - to all units so that the amount distributed to Equity Office is
       sufficient to enable Equity Office to pay shareholder dividends that
       will:

      -- satisfy the requirements for qualifying or re-electing as a REIT; and

      -- avoid any federal income or excise tax liability for Equity Office.

     If Equity Office is not publicly traded, EOP Partnership will make cash
distributions with respect to class A units at least annually for each taxable
year of EOP Partnership beginning before July 11, 2012 in an aggregate amount
that reflects at least 95% of EOP Partnership's taxable income for that year
allocable to the class A units.

     Cornerstone Partnership.  The partnership agreement of Cornerstone
Partnership requires the distribution, at least quarterly, of all or a portion
of available cash generated by the partnership during the time period.
Cornerstone will determine in its sole and absolute discretion the amount of the
distribution to be made. Distributions will be made to all partners who are
partners on the record date for the distribution in the following order:

     - first, to each partner, including Cornerstone, who holds a partnership
       interest of a class or series that is entitled to a preference according
       to the rights of that class or series of partnership interest; and

     - second, to the extent that there is available cash remaining after
       payment of any preferences, to the partners who hold a partnership
       interest that is not entitled to a preference in distribution, including
       Cornerstone Partnership units, pro rata to each class or series and,
       within each class or series, in proportion to the partner's percentage
       share of that class or series.

     Unless otherwise specifically agreed to by Cornerstone in the partnership
agreement of Cornerstone Partnership or an agreement at the time a new class or
series is created, no partnership interest will be entitled to a distribution in
preference to any other. Unless otherwise specifically agreed to by Cornerstone,
distributions payable with respect to partnership units that were not
outstanding during the entire quarterly or shorter period on which the
distribution is based will be prorated based on the portion of the period that
these units were outstanding. A Cornerstone Partnership partner will in no event
receive a distribution of available cash with respect to a partnership unit if
the partner is entitled to receive a distribution out of that same available
cash with respect to a share of Cornerstone stock for which that partnership
unit has been exchanged or redeemed.

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     Cornerstone will make reasonable efforts, as determined by it in its sole
and absolute discretion and consistent with Cornerstone's qualification as a
REIT, to distribute available cash:

     - to the limited partners so as to preclude all or a portion of the
       distribution from being treated as a part of a disguised sale for federal
       income tax purposes; and

     - to Cornerstone in amounts sufficient to enable Cornerstone to pay
       stockholder dividends that will:

      -- satisfy the requirements for qualifying or re-electing as a REIT; and

      -- avoid any federal income or excise tax liability for Cornerstone.

     As long as it would not have a negative impact on the limited partners,
Cornerstone may elect not to cause Cornerstone Partnership to distribute
sufficient amounts to enable Cornerstone to pay stockholder dividends that will
avoid federal income or excise tax liability of Cornerstone.

PREEMPTIVE RIGHTS

     EOP Partnership.  Except to the extent expressly granted by EOP Partnership
in an agreement other than the partnership agreement of EOP Partnership, no
person or entity, including any partner of EOP Partnership, has any preemptive,
preferential or other similar right with respect to:

     - additional capital contributions or loans to EOP Partnership; or

     - the issuance or sale of any EOP Partnership units or other partnership
       interests of EOP Partnership.

     Cornerstone Partnership.  Except to the extent expressly granted by
Cornerstone on behalf of Cornerstone Partnership in an agreement other than the
partnership agreement of Cornerstone Partnership, no person or entity,
including, without limitation, any partner of Cornerstone Partnership, shall
have any preemptive, preferential or other similar right with respect to:

     - additional capital contributions or loans to Cornerstone Partnership; or

     - the issuance or sale of any Cornerstone Partnership units or other
       partnership interests of Cornerstone Partnership.

CONVERSION; REDEMPTION

     EOP Partnership.  Each EOP Partnership class B unit will be converted
automatically into an EOP Partnership class A unit on the day immediately
following the record date for the distribution period during which the EOP
Partnership class B unit was issued.

     In the absence of the limitations described below, each holder of class A
units other than Equity Office and some of its affiliates has a unit redemption
right which is a right to require the redemption of its EOP Partnership class A
units by EOP Partnership. As a general rule, a limited partner may exercise the
redemption right at any time beginning on the first anniversary of the issuance
of the partnership units held by it. Specific investors described in the
partnership agreement of EOP Partnership, however only may exercise the
redemption right on the second anniversary of the issuance of EOP Partnership
units to them. Equity Office may agree to a shorter waiting period, or no
waiting period, on the exercise of the unit redemption right. Cornerstone
Partnership limited partners who receive EOP Partnership class A units in the
partnership merger will be permitted to exercise the unit redemption right at
any time following the partnership merger.

     In addition, each limited partner may exercise its unit redemption right,
regardless of the length of time it has held its EOP Partnership units, during
the period commencing on the date Equity Office has given the limited partners
notice of its intention to make an extraordinary distribution of cash or
property to its shareholders or effect a merger, a sale of all or substantially
all of its assets, or any other similar extraordinary transaction, which notice
must be given at least 20 business days prior to the record date for determining
shareholders eligible to receive the distribution or to vote upon the approval
of the merger,
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sale or other extraordinary transaction, and ending on such record date. Equity
Office, in its sole discretion, may shorten the required notice period of not
less than twenty business days prior to the record date to determine the
shareholders eligible to vote upon a merger transaction (but not any of the
other covered transactions) by up to ten business days (thereby continuing to
afford the holders of units the opportunity to redeem units on or prior to the
record date for the shareholder vote on the merger transaction) so long as (a)
Equity Office will be the surviving entity in such merger transaction, (b)
immediately following the merger transaction, persons who held voting securities
of Equity Office immediately prior to such merger transaction will hold, solely
by reason of the ownership of voting securities of Equity Office immediately
prior to the merger transaction, voting securities of Equity Office representing
not less than 51% of the total combined voting power of all outstanding voting
securities of Equity Office after such merger, and (c) in the event that in
connection with such merger transaction EOP Partnership will merge with another
entity, EOP Partnership will be the surviving entity in such merger. If no
record date as described is applicable, the date shall be at least 20 business
days before the consummation of the merger, sale or other extraordinary
transaction.

     A limited partner may exercise its unit redemption right by giving written
notice to EOP Partnership and Equity Office. The EOP Partnership units specified
in the notice shall be redeemed on the 10th business day following the date
Equity Office received the redemption notice or, in the case of the exercise of
a unit redemption right in connection with an extraordinary transaction, the
date EOP Partnership and Equity Office received the redemption notice.

     A notice of redemption delivered to EOP Partnership by the limited partner
exercising the right will exercise the redemption right. A limited partner may
not exercise the redemption right for fewer than 1,000 partnership units, or if
the limited partner holds fewer than 1,000 partnership units, all of the
partnership units held by that limited partner. The redeeming partner will have
no right to receive any distributions paid on or after the redemption date with
respect to those partnership units redeemed.

     Unless Equity Office elects to assume and perform EOP Partnership's
obligation with respect to the unit redemption right, as described below, a
limited partner which exercises its unit redemption right will receive cash from
EOP Partnership in an amount equal to the market value of the EOP Partnership
units to be redeemed. The market value of an EOP Partnership unit for this
purpose will be equal to the average of the closing trading price of an Equity
Office common share on the NYSE for the ten trading days before the day on which
the redemption notice was given.

     Instead of EOP Partnership acquiring the units being redeemed for cash,
Equity Office has the right to elect to acquire on the redemption date the EOP
Partnership units directly from a limited partner exercising the unit redemption
right in exchange for either cash in the amount specified above or a number of
Equity Office common shares equal to the number of EOP Partnership units offered
for redemption, adjusted as specified in the partnership agreement of EOP
Partnership to take into account prior share dividends or any subdivisions or
combinations of Equity Office common shares. No redemption or exchange can occur
if delivery of common shares by Equity Office would be prohibited either under
the provisions of Equity Office's Declaration of Trust or under applicable
federal or state securities laws, regardless of whether Equity Office would in
fact elect to assume and satisfy the unit redemption right. Equity Office will
at all times reserve and keep available out of its authorized but unissued
Equity Office common shares, solely for the purpose of effecting the issuance of
Equity Office common shares through a unit redemption right, a number of Equity
Office common shares that would be sufficient for the redemption of all
outstanding EOP Partnership units not owned by Equity Office.

     Unless Equity Office exercises its right to purchase the redeeming
partner's EOP Partnership units, as described above, Equity Office has no
obligation to the redeeming partner with respect to the redeeming partner's unit
redemption right. Likewise, if Equity Office exercises this purchase option, EOP
Partnership has no obligation to pay any amount to the redeeming partner with
respect to the unit redemption right. If Equity Office elects to assume and
perform the obligations of EOP Partnership under the unit redemption right, each
of the redeeming partner, EOP Partnership and Equity Office will treat this
transaction

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between Equity Office and the redeeming partner, for federal tax purposes, as a
sale of the redeeming partner's EOP Partnership units to Equity Office.

     If any Equity Office preferred shares have been called for redemption, a
number of EOP Partnership preferred units equal to the number of Equity Office
preferred shares called for redemption will be redeemed. The redemption shall
occur at a time and in a manner that allows the redemption of Equity Office
preferred shares to be completed in a timely fashion to comply with the
applicable requirements related to the share redemption.

     All EOP Partnership units delivered for redemption must be delivered to EOP
free and clear of all liens.

     Cornerstone Partnership.  Each holder of Cornerstone Partnership units,
other than Cornerstone, has a unit redemption right which requires Cornerstone
Partnership to redeem on a specified date all or a portion of the Cornerstone
Partnership units held by that limited partner for cash in an amount equal to
the value of one share of Cornerstone stock for each Cornerstone Partnership
unit being redeemed. Each limited partner may exercise this right:

     - any time on or after the day following the first anniversary of the date
       its Cornerstone Partnership units were issued or, in the case of
       Cornerstone Partnership units issued to an additional limited partner in
       December 1998, on or after the earlier of:

      -- the first anniversary of the date that the partnership interest was
         issued or

      -- a change in control of Cornerstone; or

     - any date prior to the first anniversary that Cornerstone designates with
       respect to any units then outstanding.

     A notice of redemption delivered to Cornerstone Partnership by the limited
partner is necessary to exercise the unit redemption right. A limited partner
may not exercise the unit redemption right for fewer than 1,000 partnership
units, or if the limited partner holds fewer than 1,000 partnership units, all
of the partnership units held by that limited partner. The redeeming partner
will have no right to receive any distributions paid on or after the redemption
date with respect to those partnership units redeemed.

     Unless Cornerstone elects to assume and perform Cornerstone Partnership's
obligation with respect to the unit redemption right, as described below, a
limited partner which exercises its unit redemption right will receive cash from
Cornerstone Partnership in an amount equal to the value of one share of
Cornerstone stock for each Cornerstone Partnership unit being redeemed.

     Instead of Cornerstone Partnership acquiring the Cornerstone Partnership
units for cash, Cornerstone has the right to acquire on the redemption date the
units being redeemed directly from a limited partner exercising the unit
redemption right in exchange for either cash in the amount specified above or a
number of Cornerstone common shares equal to the number of Cornerstone
Partnership units offered for redemption adjusted as specified in the
partnership agreement of Cornerstone Partnership to take into account prior
share dividends or any subdivisions or combinations of Cornerstone common
shares. No redemption or exchange can occur if delivery of common shares would
be prohibited under the provisions of Cornerstone's Certificate of
Incorporation.

     Unless Cornerstone exercises its right to purchase the redeeming partner's
Cornerstone Partnership units, as described above, Cornerstone has no obligation
to the redeeming partner with respect to the redeeming partner's unit redemption
right. Likewise, if Cornerstone exercises this purchase option, Cornerstone
Partnership has no obligation to pay any amount to the redeeming partner with
respect to the unit redemption right. If Cornerstone elects to assume and
perform the obligations of Cornerstone Partnership under the unit redemption
right, each of the redeeming partner, Cornerstone Partnership and Cornerstone
will treat this transaction between Cornerstone and the redeeming partner, for
federal income tax purposes, as a sale of the redeeming partner's Cornerstone
Partnership units to Cornerstone.

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     If any Cornerstone preferred shares are redeemed for cash, a number of
Cornerstone Partnership preferred units equal to the number of Cornerstone
preferred shares so redeemed will be redeemed. The redemption shall occur at a
time and in a manner that allows the redemption of Cornerstone preferred shares
to be completed in a timely fashion to comply with the applicable requirements
related to the share redemption.

     All Cornerstone Partnership units delivered for redemption must be
delivered to Cornerstone free and clear of all liens.

MANAGEMENT

     EOP Partnership.  Except as otherwise expressly provided in the partnership
agreement of EOP Partnership, the business and affairs of EOP Partnership are
managed by Equity Office, which has the exclusive right and full authority and
responsibility to manage and operate the partnership's business. Limited
partners do not have any right to participate in or exercise control or
management power over the business and affairs of EOP Partnership or the power
to sign documents for or otherwise bind EOP Partnership. Equity Office has full
power and authority to do all things it deems necessary or desirable to conduct
the business of EOP Partnership. However, the consent of the limited partners to
some limited matters is necessary in limited circumstances. In particular,
Equity Office is under no obligation to consider the tax consequences to limited
partners when making decisions for the benefit of EOP Partnership. The limited
partners have no power to remove Equity Office as general partner. Equity
Office, however, may not take any action that is contrary to an express
limitation or prohibition in the partnership agreement of EOP Partnership
without the written consent of:

     - all partners adversely affected; or

     - the lower percentage of the limited partners as may be specifically
       provided for in the partnership agreement of EOP Partnership.

     Cornerstone Partnership.  Except as otherwise expressly provided in the
partnership agreement of Cornerstone Partnership, the business and affairs of
Cornerstone Partnership are managed by Cornerstone, which has the exclusive
right and full authority and responsibility to manage and operate the
partnership's business. Limited partners do not have any right to participate in
or exercise control or management power over the business and affairs of
Cornerstone Partnership or the power to sign documents for or otherwise bind
Cornerstone Partnership. Cornerstone has full power and authority to do all
things it deems necessary or desirable to conduct the business of Cornerstone
Partnership. However, the consent of the limited partners to some matters is
necessary in limited circumstances. For example, Cornerstone is under no
obligation to consider the tax consequences to limited partners when making
decisions for the benefit of Cornerstone Partnership. However, if a merger would
cause adverse tax consequences to specified limited partners of Cornerstone
Partnership, written consent of those limited partners may be required. The
limited partners have no power to remove Cornerstone as the general partner.
Cornerstone, however, may not take any action that is contrary to an express
limitation or prohibition in the partnership agreement of Cornerstone
Partnership without the written consent of the limited partners holding a
majority of the Cornerstone Partnership units, including Cornerstone Partnership
units owned by Cornerstone.

SALE OF SUBSTANTIALLY ALL OF THE PARTNERSHIP ASSETS

     EOP Partnership.  A sale of all or substantially all of the assets of EOP
Partnership in a single transaction or a series of related transactions,
including by way of a merger, consolidation or other combination of EOP
Partnership with another entity, will require the following:

     - if the transaction is in connection with a similar transaction involving
       Equity Office which has also been approved by a majority of the
       outstanding EOP Partnership units, including EOP Partnership units held
       directly or indirectly by Equity Office, and in connection with which all
       limited partners have the right to receive consideration which, on a per
       unit basis, is equivalent in value to the consideration to be received by
       the shareholders of Equity Office on a per share basis, approval by a

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       majority of the outstanding EOP Partnership units, including EOP
       Partnership units held directly or indirectly by Equity Office; or

     - in the case of any other transaction, the approval of a majority of the
       outstanding EOP Partnership units held by persons or entities other than
       Equity Office and some of its affiliates.

     Cornerstone Partnership.  The partnership agreement of Cornerstone
Partnership does not contain a direct limitation on a sale or other disposition
by Cornerstone Partnership of all or substantially all of its assets. The
partnership agreement of Cornerstone Partnership, however, contains limitations
on "extraordinary transactions" involving Cornerstone that may limit most
transfers of all or substantially all of the assets of Cornerstone Partnership.

INDEMNIFICATION

     EOP Partnership.  EOP Partnership will indemnify, to the fullest extent
provided by law, any person or entity made a party to a proceeding by reason of
its status as a general partner, a limited partner or a trustee, director or
officer of Equity Office or EOP Partnership and any other persons or entities as
Equity Office may designate, in its sole discretion, from and against any and
all losses, claims, damages, liabilities, joint or several, expenses. Expenses
include, without limitation, attorneys' fees and other legal fees and expenses,
judgments, fines, settlements and other amounts arising from or in connection
with any and all claims, demands, actions, suits or proceedings, civil,
criminal, administrative or investigative, incurred by the indemnitee and
relating to EOP Partnership or Equity Office or the operation of, or the
ownership of property by, either Equity Office or EOP Partnership, as described
in the partnership agreement of EOP Partnership, in which the indemnitee may be
involved, or is threatened to be involved, as a party or otherwise, unless it is
established by a final determination of a court of competent jurisdiction that:

     - the act or omission of the indemnitee was material to the matter giving
       rise to the proceeding and either was committed in bad faith or was the
       result of active and deliberate dishonesty;

     - the indemnitee actually received an improper personal benefit in money,
       property or services, or

     - in the case of any criminal proceeding, the indemnitee had reasonable
       cause to believe that the act or omission was unlawful.

     Any indemnification will be made only out of the assets of EOP Partnership
and any insurance proceeds from the liability policy covering Equity Office or
EOP Partnership. Indemnitees, Equity Office, and limited partners will have no
obligation to contribute to the capital of EOP Partnership or otherwise provide
funds to enable EOP Partnership to fund its indemnity obligations.

     EOP Partnership is obligated to advance amounts to an indemnitee for
expenses upon receipt of:

     - a written affirmation of the indemnitee that it believes it has met the
       standard of conduct necessary to entitle it to indemnification, and

     - a written undertaking of the indemnitee that it will repay any advances
       if it shall be ultimately determined that the indemnitee did not meet the
       appropriate standard of conduct.

     These indemnification rights are in addition to any other rights afforded
to an indemnitee under any other agreement, by vote of the partners, under
applicable law or otherwise. These rights will continue as to an indemnitee who
has ceased to serve unless otherwise provided in a written agreement under which
indemnitees are indemnified. EOP Partnership is authorized to purchase and
maintain insurance on behalf of the indemnitees with respect to the foregoing
matters.

     EOP Partnership will be deemed to have requested an indemnitee to serve as
fiduciary of an employee benefit plan whenever the performance by it of its
duties to EOP Partnership also imposes duties on it, or otherwise involves
services by it, to the plan or participants or beneficiaries of the plan. Excise
taxes assessed on an indemnitee with respect to an employee benefit plan
according to applicable law will constitute fines. Actions taken or omitted by
the indemnitee with respect to an employee benefit plan in the performance of
its duties for a purpose reasonably believed by it to be in the interest of the
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participants and beneficiaries of the plan will be deemed to be for a purpose
which is not opposed to the best interests of EOP Partnership.

     An indemnitee will not be denied indemnification in whole or in part
because the indemnitee had an interest in the transaction with respect to which
the indemnification applies if the transaction was otherwise permitted by the
terms of the partnership agreement of EOP Partnership.

     Cornerstone Partnership.  Cornerstone Partnership will indemnify, to the
fullest extent provided by Delaware law, each indemnitee from and against any
and all losses, claims, damages, liabilities, joint or several, expenses,
judgments, fines, settlements, and other amounts arising from any and all
claims, demands, actions, suits or proceedings, civil, criminal, administrative
or investigative, that relate to the operations of Cornerstone Partnership.
Expenses include, without limitation, attorney's fees and other legal fees and
expenses. Indemnification will occur whether the indemnitee is involved or
threatened to be involved as a party or otherwise. Indemnification will occur
unless it is established that:

     - the act or omission of the indemnitee was material to the matter giving
       rise to the proceeding and either was committed in bad faith or was the
       result of active and deliberate dishonesty;

     - the indemnitee actually received an improper personal benefit in money,
       property, or services; or

     - in the case of any criminal proceeding, the indemnitee had reasonable
       cause to believe that the act or omission was unlawful.

     Any indemnification will be made only out of the assets of Cornerstone
Partnership and any insurance proceeds from the liability policy covering
Cornerstone or Cornerstone Partnership. Neither Cornerstone nor the limited
partners shall have an obligation to contribute to the capital of Cornerstone
Partnership or otherwise provide funds to enable Cornerstone Partnership to fund
its indemnity obligations. It is the intent of the partners that any amounts
paid by Cornerstone Partnership to Cornerstone for indemnification will be
treated as "guaranteed payments" within the meaning of section 707(c) of the
Internal Revenue Code.

     Cornerstone Partnership is obligated to advance amounts to an indemnitee
for expenses upon receipt of:

     - a written affirmation by the indemnitee that it believes in good faith it
       has met the standard of conduct necessary to entitle it to
       indemnification; and

     - a written undertaking by or on behalf of the indemnitee to repay the
       amount if it is ultimately determined that the indemnitee did not meet
       the appropriate standard of conduct.

     These indemnification rights are in addition to any other rights afforded
to an indemnitee under any other agreement, by vote of the partners, under
applicable law or otherwise. These rights will continue as to an indemnitee who
has ceased to serve unless otherwise provided in a written agreement under which
indemnitees are indemnified. Cornerstone Partnership is authorized to purchase
and maintain insurance on behalf of the indemnitees.

     Cornerstone Partnership will be deemed to have requested an indemnitee to
serve as fiduciary of an employee benefit plan whenever the performance by it of
its duties to Cornerstone Partnership also imposes duties on it, or otherwise
involves services by it, to the plan or participants or beneficiaries of the
plan. Excise taxes assessed on an indemnitee with respect to an employee benefit
plan according to applicable law will constitute fines and are eligible for
indemnification. Actions taken or omitted by the indemnitee with respect to an
employee benefit plan in the performance of its duties for a purpose reasonably
believed by it to be in the interest of the participants and beneficiaries of
the plan will be deemed to be for a purpose which is not opposed to the best
interests of Cornerstone Partnership.

     An indemnitee will not be denied indemnification in whole or in part solely
because the indemnitee had an interest in the transaction with respect to which
the indemnification applies if the transaction was otherwise permitted by the
terms of the partnership agreement of Cornerstone Partnership.

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TRANSFERS

     EOP Partnership.  Equity Office may not transfer any of its partnership
interests, including any of its limited partnership interests, except in
connection with a merger, consolidation or other combination with or into
another person, a sale of all or substantially all of its assets or any
reclassification, recapitalization or change of its outstanding shares and only
if the transaction has been approved by the consent of the partners holding at
least a majority of the then outstanding EOP Partnership units, including any
EOP Partnership units held by Equity Office and in connection with which all
limited partners have the right to receive consideration which, on a per unit
basis, is equivalent in value to the consideration to be received by the
shareholders of Equity Office, on a per share basis. Equity Office will not
withdraw from EOP Partnership except in connection with a transaction as
described in the preceding sentence.

     A limited partner, other than Equity Office, may transfer, with or without
the consent of Equity Office, all or any portion of its partnership interest, or
any of its economic rights as a limited partner, if:

     - the transfer does not violate any federal or state securities laws or
       regulations applicable to EOP Partnership or the EOP Partnership units;
       or

     - the transfer does not change or potentially affect adversely the tax
       status of EOP Partnership.

     In the case of a proposed transfer of units to a lender to EOP Partnership
or any person related to the lender whose loan constitutes a nonrecourse
liability, the transferring partner must obtain the consent of Equity Office.

     No transferee of a limited partnership interest will be admitted as a
limited partner without the consent of Equity Office, which may be given or
withheld in its sole and absolute discretion.

     Cornerstone Partnership.  Cornerstone may not engage in an extraordinary
transaction, transfer or withdraw its general partnership interest or transfer
its limited partnership interests, unless:

     - the transfer is permitted under the Cornerstone Partnership agreement;

     - the transaction has been approved by the consent of the partners that
       hold three-fourths of the outstanding Cornerstone Partnership units,
       other than units held by Cornerstone or its affiliates; or

     - the transfer is to an entity that is wholly owned by Cornerstone and is a
       qualified REIT subsidiary.

     The partnership agreement of Cornerstone Partnership defines an
extraordinary transaction as any one of the following involving Cornerstone: a
merger, consolidation or other combination; a direct or indirect sale, lease,
exchange or other transfer of all or substantially all assets in one transaction
or a series of transactions; a reclassification, recapitalization or change of
equity interests; a change of control; or an adoption of a plan of liquidation
or dissolution.

     In addition to the above, Cornerstone may engage in an extraordinary
transaction if it would fall into one the following categories:

     - a transaction in connection with which all the limited partners either
       will receive, or will have the right to receive, consideration which, on
       a per unit basis, is equivalent in value to the consideration received by
       the Cornerstone stockholders taking into account prior share dividends or
       subdivisions or combinations of the Cornerstone shares. If in connection
       with the transaction, a purchase, tender or exchange offer was made to
       and accepted by more than 50% of the Cornerstone shares, each limited
       partner will receive, or will have the right to receive, consideration
       equivalent to the value of what it would have received had it redeemed
       its Cornerstone Partnership units and received shares of Cornerstone
       common stock immediately before the offer expired and accepted the offer
       before the transaction was consummated; or

     - a merger, or other combination of assets with another entity, in which:

      -- immediately after the transaction, substantially all of the assets
         directly or indirectly owned by the surviving entity, other than the
         Cornerstone Partnership units held by Cornerstone, are

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         owned directly or indirectly by Cornerstone Partnership or another
         limited partnership or limited liability company which is the survivor
         of a merger, consolidation or combination of assets with Cornerstone
         Partnership;

      -- the limited partners own a percentage interest of the surviving entity
         based on the relative fair market value of the net assets of
         Cornerstone Partnership and the other net assets of the surviving
         entity;

      -- the rights, preferences and privileges of the limited partners in the
         surviving entity are at least as favorable as those in effect
         immediately prior to the transaction or as those applicable to any
         other limited partners or non-managing member of the surviving entity;
         and

      -- the limited partners have the right to exchange their interests in the
         surviving entity for the consideration described above or, if the
         surviving entity is publicly traded, for the common equity securities
         with an exchange ratio based on the relative fair market value of those
         securities and Cornerstone shares.

     Cornerstone will not consummate an extraordinary transaction in connection
with which it conducted a vote of Cornerstone stockholders unless there is a
corresponding vote of the partners of Cornerstone Partnership. In the
corresponding vote, Cornerstone must vote all of its partnership interests in
the same proportion and manner that its outstanding capital stock was voted in
the stockholder vote. In order for the transaction to be approved, the total
votes voted by Cornerstone and the limited partners must be sufficient to
approve the transaction as if it were a vote by Cornerstone's stockholders to
approve the transaction. Each holder of a partnership interest will be entitled
to the number of votes that the holder would be entitled to if it exercised its
right to redeem its partnership interest and were to have received shares of
Cornerstone stock.

     A limited partner, other than Cornerstone, may transfer, with or without
the consent of Cornerstone, all or any portion of its partnership interest, or
any of its economic rights as a limited partner, if:

     - the transfer does not require filing of a registration statement and does
       not violate any federal or state securities laws or regulations
       applicable to Cornerstone Partnership or the Cornerstone Partnership
       units; or

     - the transfer does not change or potentially affect adversely the tax
       status of Cornerstone Partnership.

     In the case of a proposed transfer to a lender to Cornerstone Partnership
or any person related to a lender whose loan constitutes a nonrecourse
liability, the transferring partner must obtain the consent of Cornerstone.

     No transferee of a limited partnership interest will be admitted as a
limited partner without the consent of Cornerstone, which may be given or
withheld in its sole and absolute discretion.

AMENDMENT OF PARTNERSHIP AGREEMENT

     EOP Partnership.  Amendments to the partnership agreement of EOP
Partnership may be proposed by Equity Office or by limited partners owning at
least 25% of the total partnership interests. Except as described below, the
partnership agreement of EOP Partnership may be amended with the approval of
Equity Office and limited partners holding a majority of the partnership
interests held by the limited partners, including Equity Office. Equity Office
has the power, without the consent of the limited partners, to amend the
partnership agreement of EOP Partnership as may be required:

     - to add to the obligations of the general partner or surrender any right
       or power granted to Equity Office or any affiliate of Equity Office for
       the benefit of the limited partners;

     - to reflect the admission, substitution, termination or withdrawal of
       partners in compliance with the partnership agreement of EOP Partnership;

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     - to declare the designations, rights, powers, duties and preferences of
       the holders of any additional partnership interests issued in accordance
       with the authority granted to Equity Office;

     - to reflect a change that does not affect the limited partners in any
       material respect, or to cure any ambiguity, correct or supplement any
       provision in the partnership agreement of EOP Partnership not
       inconsistent with law or with other provisions of the partnership
       agreement of EOP Partnership, or make other changes with respect to
       matters arising under the partnership agreement of EOP Partnership that
       will not be inconsistent with law or with the provisions of the
       partnership agreement of EOP Partnership; and

     - to satisfy any requirements, conditions or guidelines contained in any
       order, directive, opinion, ruling or regulation of a federal, state or
       local law.

     The approval of a majority of the partnership interests held by limited
partners other than Equity Office is necessary to amend provisions regarding,
among other things:

     - restrictions imposed on the issuance of additional EOP Partnership units
       or other partnership interests to Equity Office;

     - distribution requirements with respect to the EOP Partnership class A
       units if Equity Office is not publicly traded;

     - the prohibition against removal of Equity Office by the limited partners;

     - restrictions on Equity Office's power to conduct businesses other than
       owning partnership interests of EOP Partnership;

     - limitations on transactions with affiliates;

     - the liability of Equity Office for monetary damages to EOP Partnership;

     - partnership consent requirements for the sale of substantially all the
       assets of EOP Partnership; or

     - the transfer of partnership interests held by Equity Office, the
       admission and rights of substituted limited partners or the dissolution
       of EOP Partnership.

     Any amendment of the provision of the partnership agreement of EOP
Partnership which allows the voluntary dissolution of EOP Partnership before
December 31, 2046 can be made only with the approval of 90% of the outstanding
partnership interests, including partnership interests held by Equity Office.

     Amendments to the partnership agreement of EOP Partnership that would,
among other things:

     - convert a limited partner's interest into a general partner's interest;

     - modify the limited liability of a limited partner;

     - alter the interest of a partner in profits or losses, or the right to
       receive any distributions, except as permitted under the partnership
       agreement of EOP Partnership with respect to the admission of new
       partners or the issuance of additional EOP Partnership units; or

     - alter the unit redemption right of the limited partners of EOP
       Partnership,

must be approved by each limited partner that would be adversely affected by the
amendment.

     Cornerstone Partnership.  Only Cornerstone may propose amendments to the
partnership agreement of Cornerstone Partnership. Except as described below, the
partnership agreement of Cornerstone Partnership may be amended with the
approval of Cornerstone and the approval of limited partners holding a majority
of the Cornerstone Partnership units, including Cornerstone. Cornerstone has the
power, without the consent of the limited partners, to amend the partnership
agreement of Cornerstone Partnership as may be required:

     - to add to the obligations of Cornerstone or surrender any right or power
       granted to Cornerstone or any affiliate of Cornerstone for the benefit of
       the limited partners;
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     - to reflect the admission, substitution, termination or withdrawal of
       partners in compliance with the partnership agreement of Cornerstone
       Partnership;

     - to declare the designations, rights, powers, duties and preferences of
       the holders of any additional partnership interests issued according to
       the authority of Cornerstone;

     - to reflect a change that does not affect the limited partners in any
       material respect, or to cure any ambiguity, correct or supplement any
       provision in the partnership agreement of Cornerstone Partnership not
       inconsistent with law or with other provisions of the partnership
       agreement of Cornerstone Partnership, or make other changes with respect
       to matters arising under the partnership agreement of Cornerstone
       Partnership that will not be inconsistent with law or with the provisions
       of the partnership agreement; and

     - to satisfy any requirements, conditions or guidelines contained in any
       order, directive, opinion, ruling or regulation of a federal, state or
       local law.

     The approval of a majority of the Cornerstone Partnership units held by
limited partners other than Cornerstone is necessary to amend provisions
regarding, among other things:

     - restrictions imposed on the issuance of additional Cornerstone
       Partnership units or other partnership interests to Cornerstone;

     - restrictions on Cornerstone's power to conduct businesses other than
       owning partnership interests of Cornerstone Partnership;

     - limitations on Cornerstone or Cornerstone Partnership transactions with
       affiliates;

     - limitations on Cornerstone to transfer its general partnership interest
       or to enter into extraordinary transactions; or

     - the meetings of the partners.

     Amendments to the partnership agreement of Cornerstone Partnership that
would, among other things:

     - convert a limited partner's interest into a general partner's interest;

     - modify the limited liability of a limited partner in a manner adverse to
       such partner;

     - alter the interest of a partner in profits or losses, or the right to
       receive any distributions, except as permitted under the partnership
       agreement with respect to the admission of new partners or the issuance
       of additional Cornerstone Partnership units, or

     - alter the unit redemption right of the limited partners of Cornerstone
       Partnership,

must be approved by each limited partner that would be adversely affected by the
amendment.

MEETINGS

     EOP Partnership.  Meetings of the partners may be called by Equity Office
by written request by limited partners holding 25% or more of the partnership
interests. The call must state the nature of the business to be transacted.
Notice of any meeting is required to be given to all partners not less than
seven days nor more than 30 days before the date of the meeting. Partners may
vote in person or by proxy at the meeting. Whenever the vote or consent of
partners is permitted or required under the partnership agreement of EOP
Partnership, this vote or consent may be given at a meeting of partners. Except
as otherwise expressly provided in the partnership agreement of EOP Partnership,
the consent of a majority of the percentage interests held by limited partners,
including limited partnership interests held by Equity Office, shall control.

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     Any action required or permitted to be taken at a meeting of the partners
may be taken without a meeting if a written consent showing the action taken is
signed by a majority of the percentage interests of the partners or another
percentage as required by the partnership agreement of EOP Partnership.

     Cornerstone Partnership.  Meetings of Cornerstone Partnership may only be
called by Cornerstone. The request for a meeting must state the nature of the
business to be transacted. Notice of a meeting must be given to all partners not
less than seven nor more than thirty days before the date of the meeting.
Partners may vote in person or by proxy. Whenever the vote or consent of
partners is permitted or required under the partnership agreement of Cornerstone
Partnership, this vote or consent may be given at a meeting of partners. Except
as otherwise expressly provided in the partnership agreement of Cornerstone
Partnership, the consent of the holders of a majority of the outstanding
Cornerstone Partnership units, including Cornerstone Partnership units held by
Cornerstone (other than preferred units), shall control.

     Any action required or permitted to be taken at a meeting of the partners
may be taken without a meeting if a written consent showing the action taken is
signed by holders of a majority of the outstanding Cornerstone Partnership
units, or another percentage as required by the partnership agreement of
Cornerstone Partnership.

FINANCIAL STATEMENTS AND REPORTS

     EOP Partnership.  On or before the date on which Equity Office mails its
annual report to its shareholders, Equity Office is required to mail to each
limited partner an annual report, as of the close of the most recently ended
fiscal year of EOP Partnership, containing financial statements of EOP
Partnership, or of Equity Office if the Equity Office statements are prepared
solely on a consolidated basis with EOP Partnership, for that fiscal year.

     In addition, if Equity Office mails quarterly reports to its shareholders,
Equity Office is required to mail to each limited partner a report containing
unaudited financial statements, as of the last day of the calendar quarter, of
EOP Partnership, or of Equity Office if the Equity Office statements are
prepared solely on a consolidated basis with EOP Partnership.

     Cornerstone Partnership.  On or before the date on which Cornerstone mails
its annual report to its stockholders, Cornerstone is required to mail to each
limited partner an annual report, as of the close of the most recently ended
fiscal year of Cornerstone Partnership, containing financial statements of
Cornerstone Partnership, or of Cornerstone if the Cornerstone statements are
prepared solely on a consolidated basis with Cornerstone Partnership, for that
fiscal year.

     In addition, if and to the extent that Cornerstone mails quarterly reports
to its stockholders, on or before the date on which the reports are mailed,
Cornerstone must mail to each limited partner a report containing unaudited
financial statements, as of the last day of that calendar quarter, of
Cornerstone Partnership, or of Cornerstone if Cornerstone statements are
prepared solely on a consolidated basis with Cornerstone Partnership.

                      COMPARISON OF RIGHTS OF SHAREHOLDERS

     The following is a summary of the material differences between the rights
of holders of Equity Office common shares and holders of Cornerstone common
stock. As a Maryland real estate investment trust, Equity Office is subject to
Maryland law governing real estate investment trusts organized in Maryland. The
Maryland real estate investment trust law covers some of the same matters
covered by the Maryland General Corporation Law, including liabilities of
trustees and officers, amendment of the declaration of trust and mergers of a
Maryland real estate investment trust with other entities. There are many
corporate governance matters that are addressed in the Maryland General
Corporation Law, however, that are not dealt with in the Maryland real estate
investment trust law. It is the general practice of Maryland real estate
investment trusts to address some of these matters through provisions in the
declaration of trust or bylaws. As a Nevada corporation, Cornerstone is subject
to applicable provisions of the Nevada General Corporation Law applicable to
corporations organized in Nevada.
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     The following discussion is not intended to be complete and is qualified by
reference to the declaration of trust and bylaws of Equity Office, the articles
of incorporation and bylaws of Cornerstone and applicable Maryland and Nevada
law. The declaration of trust and bylaws of Equity Office and the articles of
incorporation and bylaws of Cornerstone are incorporated by reference in this
joint proxy statement/prospectus, and will be sent to holders of Equity Office
common shares and Cornerstone common stock upon request. See "Where You Can Find
More Information."

AUTHORIZED SHARES

     Equity Office.  The authorized shares of beneficial interest of Equity
Office consist of 750,000,000 common shares, par value $.01 per share, and
100,000,000 preferred shares, of which 8,000,000 shares are designated as "8.98%
series A cumulative redeemable preferred shares," 7,000,000 shares are
designated as "5.25% series B convertible, cumulative preferred shares" and
4,600,000 shares are designated as "8 5/8% series C cumulative redeemable
preferred shares of beneficial interest."

     Under the Equity Office declaration of trust, the Equity Office board of
trustees has the authority to issue authorized but unissued common shares or
preferred shares in one or more classes or series without shareholder approval.
The Equity Office board of trustees also is authorized to reclassify authorized
but unissued common shares into preferred shares, and authorized but unissued
preferred shares into common shares, without shareholder approval. Subject to an
express provision to the contrary in the terms of any class or series of
authorized shares, under the Equity Office declaration of trust the board of
trustees also has the power to divide or combine the outstanding shares of any
class or series, without shareholder approval. Notwithstanding the foregoing,
under the articles supplementary establishing the outstanding series A, series B
and series C preferred shares of Equity Office, the board of trustees may not
authorize, create or increase the authorized amount of any class or series of
shares ranking before the outstanding series A, series B and series C shares
with respect to the payment of distributions or upon liquidation, without the
approval of holders of two thirds of the outstanding shares of these series of
preferred shares voting together as a single class.

     At      , 2000, there were issued and outstanding      Equity Office common
shares,      Equity Office series A preferred shares, Equity Office series B
convertible, cumulative preferred shares and
Equity Office series C preferred shares.

     Cornerstone.  The authorized stock of Cornerstone consists of 250,000,000
shares of common stock, without par value, and 65,000,000 shares of preferred
stock, without par value, of which 3,030,303 shares are designated as "7%
cumulative convertible preferred stock" and 344,828 shares are designated as
"redeemable preferred stock."

     Under the Cornerstone articles of incorporation, the Cornerstone board of
directors has the authority to issue authorized but unissued common shares or
preferred shares in one or more series without stockholder approval.

     At      , 2000, there were issued and outstanding          shares of
Cornerstone common stock and 3,030,303 shares of Cornerstone 7% cumulative
convertible preferred stock.

VOTING RIGHTS

     Equity Office.  Each holder of Equity Office common shares is entitled to
one vote per share and to the same and identical voting rights as other holders
of Equity Office common shares. Holders of Equity Office common shares do not
have cumulative voting rights. Except as provided in articles supplementary
establishing a series of Equity Office preferred shares or required by law,
holders of Equity Office preferred shares do not have any voting rights. For a
description of the voting rights of holders of outstanding series A, series B
and series C preferred shares, see "-- Authorized Shares," "-- Number of
Trustees/ Directors; Removal of Trustees/Directors; Vacancies" and "-- Amendment
of the Declaration of Trust and Articles of Incorporation."

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<PAGE>   160

     Cornerstone.  Each holder of Cornerstone common stock is entitled to one
vote per share and to the same and identical voting rights as other holders of
Cornerstone common stock. Holders of Cornerstone common stock do not have
cumulative voting rights. Except as provided by law or in the certificate of
designations creating a series of Cornerstone preferred stock, holders of
Cornerstone preferred stock do not have any voting rights.

CLASSIFICATION OF THE BOARD

     Equity Office.  The Maryland real estate investment trust law permits a
Maryland real estate investment trust's board of trustees to be divided into up
to three classes with staggered terms of office. The Equity Office declaration
of trust divides the Equity Office board of trustees into three classes, with
classes being elected to three-year terms on a rotating basis.

     Cornerstone.  The Nevada General Corporation Law permits a Nevada
corporation to divide its board of directors into up to four classes with
staggered terms of office. However, Cornerstone does not have a classified board
of directors. Accordingly, its directors serve for one-year terms and are
elected annually.

NUMBER OF TRUSTEES/DIRECTORS; REMOVAL OF TRUSTEES/DIRECTORS; VACANCIES

     Equity Office.  The Equity Office declaration of trust provides for a
minimum of nine and a maximum of 15 trustees, with the number of trustees within
this range established by a majority vote of the board of trustees as provided
in the Equity Office bylaws. Under the Equity Office bylaws, except during the
period in which a vacancy exists, at least two-thirds of the Equity Office
trustees must be persons who are not executive officers of Equity Office or
persons affiliated with Samuel Zell or his affiliates.

     Under the Equity Office declaration of trust, subject to the rights of one
or more classes or series of preferred shares to elect one or more trustees, a
trustee may be removed at any time, only with cause, at a meeting of the
shareholders by the affirmative vote of the holders of not less than a majority
of the shares then outstanding and entitled to vote generally in the election of
trustees.

     Under the Equity Office declaration of trust, subject to the rights of
holders of any class or series of preferred shares, each vacancy on the board of
trustees, including a vacancy resulting from an increase in the number of
trustees, may be filled only by the affirmative vote of a majority of the
remaining trustees in office, even if the remaining trustees do not constitute a
quorum. Any trustee elected to fill a vacancy will hold office for the remainder
of the full term of the class of trustees in which the vacancy occurred and
until a successor is elected and qualifies.

     The holders of the outstanding shares of series A, series B and series C
preferred shares of Equity Office are entitled, voting together as a single
class, to elect a total of two trustees to the Equity Office board of trustees
at any time distributions on the preferred shares were in arrears for six or
more quarterly periods.

     Cornerstone.  Cornerstone's articles of incorporation provide for a minimum
of three and a maximum of eighteen members of Cornerstone's board of directors.
At present, Cornerstone's board stands at fourteen members. The size of the
board may be increased or decreased by action of the board of directors and,
during certain periods set forth in Cornerstone's bylaws, the approval of the
board affairs committee of Cornerstone's board is required to effect any such
change. Cornerstone's bylaws also require that: (a) until December 16, 2001,
Cornerstone's board of directors shall nominate William Wilson III and two
individuals designated by Mr. Wilson for election to the board; and (b) until
the date that PGGM and its affiliated entities own, collectively, less than 5%
of Cornerstone's issued and outstanding common stock, Cornerstone's board is
required to nominate two persons designated by PGGM for election as directors.

     At least one of the two persons designated by Mr. Wilson must satisfy the
criteria for independent directors described in the New York Stock Exchange,
Inc. Listed Company Manual and must satisfy the

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criteria for non-employee directors described in rule 16b-3(b)(3)(i) promulgated
by the SEC under the Securities Exchange Act of 1934.

     Directors may be removed, with or without cause, at any time by the vote or
written consent of stockholders of record holding at least two-thirds of the
shares of Cornerstone's issued and outstanding common stock.

     Vacancies on Cornerstone's board may be filled by the affirmative vote or
written consent of stockholders of record holding at least a majority of the
shares of Cornerstone's issued and outstanding common stock or by vote or
written consent of Cornerstone's board, whether or not sufficient directors are
in office to constitute a quorum. During the periods referred to above in which
either Mr. Wilson or PGGM has a right to designate persons for nomination to the
board of directors, if a vacancy on Cornerstone's board is caused by the absence
of any such person, Cornerstone's board is required to fill the vacancy with a
person designated by Mr. Wilson or PGGM, as the case may be. Any director
elected to fill a vacancy on Cornerstone's board will hold office for the
remainder of the full term of the absent director.

     If dividends payable on Cornerstone's 7% cumulative convertible preferred
stock are in arrears for an aggregate number of days equal to six calendar
quarters or more, whether or not consecutive, the holders of such stock have the
right to elect two members of Cornerstone's board of directors at the next
annual meeting of shareholders and at each subsequent meeting of shareholders
until such arrearages have been paid or set apart for payment.

LIMITATION OF TRUSTEE/DIRECTOR AND OFFICER LIABILITY

     Equity Office.  Under Maryland law, the declaration of trust of a Maryland
real estate investment trust may include a provision expanding or limiting the
liability of its trustees and officers to the trust or its shareholders for
money damages but may not include a provision which restricts or limits the
liability of its trustee or officers to the trust or its shareholders to the
extent that:

     - it is proved that the person actually received an improper benefit or
       profit in money, property or services, for the amount of the benefit or
       profit in money, property or services actually received; or

     - a judgment or other final adjudication adverse to the person is entered
       in a proceeding based on a finding that the person's action, or failure
       to act, was the result of active and deliberate dishonesty and was
       material to the cause of action adjudicated in the proceeding.

     The Equity Office declaration of trust provides that, to the maximum extent
that Maryland law, no trustee or officer of Equity Office shall be liable to
Equity Office or to any shareholder for money damages.

     Cornerstone.  Nevada law allows a corporation to provide in its articles of
incorporation that the personal liability of the corporation's directors to its
stockholders or the corporation is limited, but such a provision may not extend
to intentional misconduct, fraud or a knowing violation of law or payments of
distributions to the corporation's shareholders which are not allowed by Nevada
law. Cornerstone's articles of incorporation do not contain any such provision
limiting director liability.

INDEMNIFICATION

     Equity Office.  Maryland law generally permits a Maryland real estate
investment trust to indemnify any person made a party to any threatened, pending
or completed action, suit or proceeding by reason of the fact that the person is
or was a trustee, officer, employee or agent of the trust or any predecessor
entity, or is or was serving at the request of the trust or predecessor entity
as a director, officer, partner, trustee, employee or agent of another
corporation, partnership, joint venture, trust, other enterprise or employee
benefit plan, unless it is established that:

     - the act or omission was material to the matter giving rise to the
       proceeding and either was committed in bad faith or was the result of
       active and deliberate dishonesty;
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     - the person actually received an improper personal benefit in money,
       property or services; or

     - in the case of any criminal proceeding, the person had reasonable cause
       to believe that the act or omission was unlawful.

     Under Maryland law, indemnity may be provided against judgments, penalties,
fines, settlements and reasonable expenses actually incurred by the person in
connection with the proceeding. The indemnification may be provided, however,
only if authorized for a specific proceeding after a determination has been made
that indemnification is permissible in the circumstances because the person met
the applicable standard of conduct. This determination is required to be made:

     - by the board of trustees by a majority vote of a quorum consisting of
       trustees not, at the time, parties to the proceeding;

     - if such quorum cannot be obtained, then by a majority vote of a committee
       of the board consisting solely of two or more trustees not, at the time,
       parties to the proceeding;

     - by special legal counsel; or

     - by the shareholders.

     If the proceeding is one by or in the right of the trust, indemnification
may not be provided as to any proceeding in which the person is found liable to
the trust.

     A Maryland real estate investment trust may pay, before final disposition,
the expenses, including attorneys' fees, incurred by a trustee, officer,
employee or agent in defending a proceeding. Under Maryland law, expenses may be
advanced to a trustee or officer when the trustee or officer gives an
undertaking to the trust to repay the amounts advanced if it is ultimately
determined that he or she is not entitled to indemnification. Maryland law does
not require that the undertaking be secured and the undertaking may be accepted
without reference to the financial ability of the trustee or officer to repay
the advance. A Maryland trust is required to indemnify any trustee who has been
successful, on the merits or otherwise, in defense of a proceeding for
reasonable expenses. The determination as to reasonableness of expenses is
required to be made in the same manner as required for indemnification.

     Under Maryland law, the indemnification and advancement of expenses
provided by statute are not exclusive of any other rights to which a person
seeking indemnification or advancement of expenses may be entitled under any
bylaw, agreement, vote of shareholders, vote of trustees or otherwise.

     Under the Equity Office bylaws, Equity Office is required to indemnify and
advance expenses to present and former trustees and officers, and may indemnify
employees and agents, of Equity Office and its predecessors. The Equity Office
bylaws also provide for mandatory indemnification and advancement of expenses to
present and former shareholders of Equity Office or its predecessors made a
party to a proceeding by reason of such status.

     The limited partnership agreement of EOP Operating Limited Partnership also
provides for indemnification of Equity Office and its officers and trustees to
the same extent that indemnification is provided to officers and trustees of
Equity Office in its declaration of trust, and limits the liability of Equity
Office and its officers and trustees to EOP Partnership and its respective
partners to the same extent that the Equity Office declaration of trust limits
the liability of the officers and trustees of Equity Office to Equity Office and
its shareholders.

     Cornerstone.  Section 78.7502 of Chapter 78 of the Nevada Revised Statutes
allows Cornerstone to indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action or
suit or proceeding, whether civil, criminal, administrative or investigative,
other than an action by or in the right of the corporation, by reason of the
fact that he or she is or was a director, officer, employee or agent of the
corporation or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation or other enterprise,
against expenses,

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including attorneys' fees, and against judgments, fines and amounts paid in
settlement actually and reasonably incurred by him or her in connection with
such action, suit or proceeding if:

     - he or she acted in good faith and in a manner he or she reasonably
       believed to be in, or not opposed to, the best interests of the
       corporation; and

     - with respect to any criminal action or proceeding, he or she had no
       reasonable cause to believe his or her conduct was unlawful.

     The termination of any action, suit or proceeding by judgment, order,
settlement or conviction or upon a plea of nolo contendere or its equivalent
does not, of itself, create a presumption that the person did not act in good
faith or in a manner which he or she reasonably believed to be in, or not
opposed to, the best interests of the corporation or that, with respect to any
criminal action or proceeding, he or she had reasonable cause to believe his or
her actions were unlawful.

     Section 78.7502 of the Nevada Revised Statutes allows Cornerstone to
indemnify any person who was or is a party or is threatened to be made a party
to any threatened, pending or completed action or suit by or in the right of the
corporation to procure a judgment in its favor by reason of the fact that such
person acted in any of the capacities described above against expenses,
including attorneys' fees, actually and reasonably incurred by him or her in
connection with the defense or settlement of such action or suit if he or she
acted under similar standards to those described above, except that no
indemnification may be made in respect of:

     - any claim, issue or matter as to which such person shall have been
       adjudged to be liable to the corporation; or

     - amounts paid in settlement to the corporation, unless and only to the
       extent that the court in which such action or suit was brought determines
       that, despite the adjudication of liability, such person is fairly and
       reasonably entitled to indemnity for such expenses as the court deems
       proper.

     Section 78.7502 of the Nevada Revised Statutes further provides that to the
extent a director or officer of a corporation has been successful in the defense
of any action, suit or proceeding referred to above or in the defense of any
claim, issue or matter therein, he or she shall be indemnified against expenses,
including attorneys' fees, actually and reasonably incurred by him or her in
connection therewith. Article IX of Cornerstone's bylaws provides for
indemnification of its officers and directors that is substantially identical in
scope to the foregoing discussion of the Nevada Revised Statutes.

     Section 78.751 of the Nevada Revised Statutes provides that any
indemnification provided for by section 78.7502 of the Nevada Revised Statutes,
by court order or otherwise, shall not be deemed to be exclusive of any other
rights to which the indemnified party may be entitled and that the scope of
indemnification shall continue as to directors, officers, employees or agents
who have ceased to hold such positions, and to their heirs, executors and
administrators. Cornerstone's bylaws also provide, pursuant to section 78.7502
of the Nevada Revised Statutes, that the expenses of officers and directors
incurred in defending any action, suit or proceeding, whether civil, criminal,
administrative or investigative, must be paid by Cornerstone as they are
incurred and in advance of the final disposition of the action, suit or
proceeding, provided that Cornerstone receives an undertaking by or on behalf of
the director or officer to repay such amounts unless it shall ultimately be
determined that he or she is entitled to be indemnified by Cornerstone pursuant
to Article IX of its bylaws.

     Finally, section 78.752 of the Nevada Revised Statutes allows Cornerstone
to purchase and maintain insurance on behalf of any of Cornerstone's directors,
officers, employees or agents against any liability asserted against any of them
in any such capacity or arising out of their status as such, whether or not
Cornerstone would have the power to indemnify them against such liabilities
under section 78.7502. Cornerstone has purchased this type of insurance in
customary amounts for its directors, officers, employees and agents.

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DUTIES OF TRUSTEES AND DIRECTORS

     Equity Office.  Recent Maryland legislation provides increased protection
for Maryland real estate investment trusts against unsolicited takeovers by
affording greater protection to a board of trustees with regard to actions taken
in a takeover context. The Maryland legislation provides that the duties of
trustees will not require them to:

     - accept, recommend, or respond to any proposal by a person seeking to
       acquire control;

     - authorize the real estate investment trust to redeem any rights under,
       modify, or render inapplicable a shareholder rights plan;

     - make a determination under the Maryland Business Combination Statute or
       the Control Share Acquisition Statute, as described below;

     - elect to be subject to any or all of the "elective provisions" described
       below; or

     - act or fail to act solely because of:

       - the effect the act or failure to act may have on an acquisition or
         potential acquisition of control; or

       - the amount or type of consideration that may be offered or paid to
         shareholders in an acquisition.

     The Maryland legislation also states the presumption that any act of a
trustee satisfies the required standard of conduct. In the case of a Maryland
corporation, these are a director's duties to act in good faith, in a manner
that is in the best interests of the corporation and with the care of an
ordinarily prudent person under similar circumstances. In the case of a Maryland
real estate investment trust, the standard of conduct is not explicitly provided
by statute. Under the Maryland legislation, an act of a trustee relating to or
affecting an acquisition or a potential acquisition of control may not be
subject to a higher duty or greater scrutiny than is applied to any other act of
a trustee. This provision creates a Maryland rule which is less exacting than
case law in many other jurisdictions which (a) imposes an enhanced level of
scrutiny when a board implements anti-takeover measures in a change of control
context; and (b) shifts the burden of proof to directors to show that the
defensive mechanism adopted by a board is reasonable in relation to the threat
posed.

     The Maryland legislation also provides that the duty of a trustee is only
enforceable by the trust or in the right of the trust. A shareholder suit to
enforce such duty, therefore, can only be brought derivatively.

     Partly in response to judicial decisions in Delaware in the takeover
context, Nevada's legislature enacted a statute providing that, in performing
their duties, directors of a corporation may consider factors other than the
short-term interests of the corporation's shareholders, including the interests
of the corporation's employees, suppliers, creditors and customers, the state
and national economy, the interests of the community and society, and the
long-term as well as short-term interests of the corporation and its
stockholders, including the possibility that these interests may be best served
by the corporation's continued independence.

     Cornerstone.  Like directors of Maryland corporations, directors of Nevada
corporations enjoy the benefit of a presumption that, in exercising their
powers, directors are acting in good faith, on an informed basis and with a view
to the interests of the corporation. The required standard of care is expressly
stated in the statute: good faith with a view to the interests of the
corporation. Given, however, the case law of other jurisdictions in the
anti-takeover context, it is not clear whether a Nevada court would impose a
more exacting standard of care than that stated in the statute.

MARYLAND ELECTIVE PROVISIONS

     Equity Office.  Recent Maryland legislation allows publicly-held Maryland
corporations and Maryland real estate investment trusts to elect to be governed
by all or any part of new Maryland law provisions relating to extraordinary
actions and unsolicited takeovers. The election to be governed by one or more of

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these provisions can be made by a Maryland real estate investment trust in its
declaration of trust or bylaws or by resolution adopted by the board of trustees
as long as the trust has at last three trustees who, at the time of electing to
be subject to the provisions are not:

     - officers or employees of the trust;

     - persons seeking to acquire control of the trust;

     - directors, officers, affiliates or associates of any person seeking to
       acquire control; or

     - nominated or designated as trustees by a person seeking to acquire
       control.

     Articles supplementary must be filed with the Maryland State Department of
Assessments and Taxation if a Maryland corporation trust or elects to be subject
to any or all of the provisions by board resolution or bylaw amendment.
Shareholder approval is not required for the filing of articles supplementary.

     The Maryland legislation provides that a trust can elect to be subject to
all or any portion of the following provisions notwithstanding any contrary
provisions contained in the trust's existing declaration of trust or bylaws:

     - Classified Board: Equity Office already has a classified board;

     - Two-Thirds Shareholder Vote to Remove Trustees Only For Cause: The
       shareholders may remove any trustee only by the affirmative vote of at
       least two thirds of all the votes entitled to be cast by the shareholders
       generally in the election of directors, but a trustee may not be removed
       without cause;

     - Size of Board Fixed by Vote of Board: Equity Office already has this
       provision, subject to the range on the number of trustees contained in
       its declaration of trust;

     - Board Vacancies Filled by the Board for the Remaining Term:  Vacancies
       that result from an increase in the size of the board, or the death,
       resignation, or removal of a trustee, may be filled only by the
       affirmative vote of a majority of the remaining trustees even if they do
       not constitute a quorum. Trustees elected to fill vacancies shall hold
       office for the remainder of the full term of the class of directors in
       which the vacancy occurred (as opposed to until the next annual meeting
       of shareholders) and until a successor is elected and qualifies. Equity
       Office recently adopted this provision; and

     - Shareholder Calls of Special Meetings Only Upon the Written Request of
       Holders of at Least a Majority of All Votes Entitled to be Cast:  Equity
       Office already has this provision.

     Cornerstone.  Although Nevada's General Corporation Law contains no similar
statute, Cornerstone's bylaws and articles of incorporation address most of the
issues addressed by the Maryland legislation described above. Other than
stockholder calls for special meetings, Cornerstone's approach to the issues
addressed by the Maryland legislation is set forth in the above section entitled
"Number of Trustees/ Directors; Removal of Trustees/Directors; Vacancies."
Nevada law does not provide for stockholder calls of special meetings. However,
Cornerstone's bylaws provide that holders of record of at least a majority of
the shares of Cornerstone's issued and outstanding common stock which are
entitled to vote at a special meeting may call such a meeting.

CALL OF SPECIAL MEETINGS OF SHAREHOLDERS

     Equity Office.  The Equity Office bylaws provide that special meetings of
shareholders may be called by the chairman of the board, the president or
one-third of the trustees. Special meetings of shareholders also may be called
by the holders of shares entitled to cast not less than a majority of all the
votes entitled to be cast at a special meeting of shareholders.

     Cornerstone.  As noted above, Cornerstone's bylaws provide that holders of
record of at least a majority of the shares of Cornerstone's issued and
outstanding common stock which are entitled to vote at
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a special meeting may call a special meeting of stockholders. In addition,
Cornerstone's bylaws allow Cornerstone's board of directors, Chairman of the
Board, President or Secretary to call a special meeting of the stockholders.

SHAREHOLDER ACTION BY WRITTEN CONSENT

     Equity Office.  The Equity Office bylaws permit any action required or
permitted to be taken at a meeting of shareholders to be taken without a meeting
if a consent in writing, setting forth the action to be taken, is signed by
shareholders entitled to cast a sufficient number of votes to approve the
matter.

     Cornerstone.  Nevada law and Cornerstone's bylaws also allow any action
required or allowed to be taken at a stockholder's meeting to be taken without a
meeting, notice or a vote of stockholders if a written consent to such action,
setting forth the action, is signed by holders of record of a majority, or if a
higher proportion would be required at a meeting of stockholders, then that
higher proportion, of the corporation's issued and outstanding shares of common
stock.

ADVANCE NOTICE PROVISIONS FOR SHAREHOLDER NOMINATIONS AND SHAREHOLDER NEW
BUSINESS PROPOSALS

     Equity Office.  The Equity Office bylaws require advance written notice for
shareholders to nominate a trustee or bring other business before a meeting of
shareholders.

     For an annual meeting, a shareholder must deliver notice to the secretary
of Equity Office not later than the close of business on the 60th day nor
earlier than the close of business on the 90th day before the first anniversary
of the preceding year's annual meeting. However, if the date of the annual
meeting is advanced by more than 30 days or delayed by more than 60 days from
the applicable anniversary date of the prior year's annual meeting, or the
meeting is a special meeting of shareholders at which trustees will be elected,
notice by the shareholder must be given not earlier than the close of business
on the 90th day before the meeting and not later than the close of business on
the later of the 60th day before the meeting or the tenth day following the day
on which public announcement of the date of the meeting is first made by Equity
Office.

     The Equity Office bylaws contain detailed requirements for the contents of
shareholder notices of trustee nominations and new business.

     Cornerstone.  Neither the Cornerstone articles of incorporation nor its
bylaws contain a comparable provision.

AMENDMENT OF THE DECLARATION OF TRUST AND ARTICLES OF INCORPORATION

     Equity Office.  Under Maryland law and the Equity Office declaration of
trust, the trustees, by a two-thirds vote, may at any time amend the declaration
of trust solely to enable Equity Office to qualify as a REIT under the Internal
Revenue Code or as a real estate investment trust under Maryland law, without
action by Equity Office shareholders. The Equity Office board of trustees also
may amend the declaration of trust to set the terms of one or more series of
preferred shares, without action by holders of Equity Office common shares.
Other amendments to the declaration of trust must first be declared advisable by
the board of trustees and thereafter must be approved by shareholders by the
affirmative vote of not less than two-thirds of all votes entitled to be cast,
or, in the case of amendments to the declaration of trust in connection with
mergers and other specified business combinations or that involve an increase or
decrease in the number of authorized common shares or preferred shares, not less
than a majority of all votes entitled to be cast.

     Under the articles supplementary for each series of outstanding preferred
shares of Equity Office, the approval of holders of each preferred series by a
two-thirds class vote would be required for:

     - the authorization, creation or increase in the authorized or issued
       amount of any class or series of Equity Office shares ranking before the
       outstanding preferred series as to distributions or upon liquidation; or

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     - any amendment, alteration or repeal of provisions of the declaration of
       trust, whether by merger, consolidation, or otherwise, so as to
       materially and adversely affect any right, preferences, privileges or
       voting power of the outstanding series of preferred shares.

     Cornerstone.  General amendments to Cornerstone's articles of incorporation
are governed by the provisions of the Nevada General Corporation Law.
Cornerstone's articles expressly provide, however, that Cornerstone's board of
directors may determine the rights, preferences, privileges, designations and
other characteristics of classes and series of Cornerstone's preferred stock.
Under the Nevada General Corporation Law, general amendments to Cornerstone's
articles of incorporation require Cornerstone's board of directors to recommend
the amendment to Cornerstone's stockholders and for holders of record of at
least a majority of the shares of Cornerstone's issued and outstanding common
stock which are entitled to vote to approve such amendment. Nevada's General
Corporation Law provides holders of classes or series of Cornerstone's preferred
stock a right to vote as a class or series on amendments to Cornerstone's
articles of incorporation, regardless of limitations on the voting rights of
such class or series, if the amendment would alter or change any preference or
relative or other right given to such a class or series.

     The certificate of designations of the only series of Cornerstone's
preferred stock of which shares are issued and outstanding, the 7% cumulative
convertible preferred stock, provides that the consent or affirmative vote of
holders of at least two-thirds of the shares of the holders thereof shall be
required to:

     (a) issue or increase the authorized amount of any class or series of
         shares ranking prior with respect to payment of dividends or
         distributions of amounts upon liquidation; or

     (b) amend, alter or repeal any provision of Cornerstone's articles of
         incorporation that would materially and adversely affect any power,
         preference or special right of the series.

     Notwithstanding (b) above, Nevada's General Corporation Law would require
the approval of the record holders of a majority of issued and outstanding
shares of the 7% cumulative convertible preferred stock that are entitled to
vote, to amend Cornerstone's articles of incorporation, whether or not the
proposed amendment would "materially" alter or change any preference or any
relative or other right given to such stock.

AMENDMENT OF THE BYLAWS

     Equity Office.  The Equity Office bylaws provide that the power to amend,
repeal or adopt new bylaws is vested exclusively with the board of trustees,
except that any amendments by the board of trustees to the bylaw provisions
relating to meetings of shareholders, the minimum and maximum number of
trustees, the requirement that at least two-thirds of the trustees must be
persons who are not executive officers of Equity Office or persons affiliated
with Samuel Zell or his affiliates are subject to the approval of shareholders
by vote of a majority of the votes cast.

     Cornerstone.  Amendment of Cornerstone's bylaws is governed by the terms of
the bylaws. The bylaws provide that amendments may be adopted either by holders
of record of a majority of the corporation's issued and outstanding shares of
common stock or by Cornerstone's board. However, until December 16, 2001,
amendments to sections 3.02 (number of directors and term), 3.03 (identity of
members of the board of directors), 3.04 (relating to the position of chairman
of the board), 3.07 (filling vacancies on the board of directors), 3.09
(relating to committees of the board of directors), and 10.01(b) (relating to
restrictions on amendment of the bylaws), require the consent of a majority of
the members of the entire board and the unanimous approval of the board affairs
committee of the board of directors. In addition, until the earlier of (a) the
date on which PGGM or Dutch Institutional Holding Company or their respective
affiliates own, collectively, less than 25% of Cornerstone's issued and
outstanding common stock and (b) October 31, 2002, amendments to sections 3.02,
3.03, 3.07, 3.09 or 10.01(c) (relating to restrictions on amendments of the
bylaws) of the bylaws require the consent of a majority of the members of the
entire board and the unanimous approval of the board affairs committee of the
board of directors. Lastly, until PGGM and its affiliated entities own,
collectively, less than 5% of the issued and outstanding shares of Cornerstone's
common stock, amendments to section 3.03(b) (relating to PGGM's right to

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designate persons for nomination to Cornerstone's board of directors) and
10.01(c) also require the consent of a majority of the members of the entire
board and the unanimous approval of the board affairs committee of the board of
directors.

MERGERS, CONSOLIDATIONS AND SALES OF ASSETS

     Equity Office.  Under Maryland law, a merger involving a Maryland real
estate investment trust generally requires approval by the affirmative vote of
not less than two-thirds of all votes entitled to be cast on the matter, unless
the declaration of trust specifies a greater or lesser percentage, but not less
than a majority. No shareholder approval is required for parent-90% owned
subsidiary mergers or by shareholders of a Maryland successor trust if the
merger does not reclassify or change the outstanding shares or otherwise amend
the declaration of trust and the number of shares to be issued in the merger is
not more than 20% of the number of its shares of the same class or series
outstanding immediately before the merger is completed. The Equity Office
declaration of trust specifies that the affirmative vote of shareholders by not
less than a majority of all votes entitled to be cast is required to approve
mergers for which a shareholder vote is required under Maryland law.

     Maryland law does not address the requirements for the approval by
shareholders of a consolidation or sale of all or substantially all of the
assets of a real estate investment trust. However, the Equity Office declaration
of trust requires that a majority of the Equity Office shares entitled to vote
on the matter must approve a consolidation of Equity Office into one or more
other entities or the sale of all or substantially all of the assets of Equity
Office outside the ordinary course of business. Under the Equity Office
declaration of trust, the mortgage, pledge or other creation of a security
interest in any or all of the assets of Equity Office, whether or not in the
ordinary course of business, as well as the sale of all or substantially all of
the assets of Equity Office to a majority owned subsidiary or as a distribution
to shareholders is not deemed to be a sale requiring shareholder approval.

     Cornerstone.  Mergers and share exchanges involving Nevada corporations are
governed by Chapter 92A of the Nevada Revised Statutes, which we refer to as the
"Merger Statute." Under the Merger Statute, Cornerstone may approve a plan of
merger or exchange of shares if (a) Cornerstone's board of directors recommends
the plan to the stockholders and (b) holders of record of a majority of
Cornerstone's common stock entitled to vote approve the plan. Approval of a
merger by Cornerstone's stockholders is not required if: (x) Cornerstone is to
be the surviving entity in a merger; (y) Cornerstone's articles of incorporation
after the merger will be the same as its articles of incorporation before the
merger; and (z) the number of shares of Cornerstone's common stock outstanding
immediately after the merger, plus the number of such shares issued as a result
of the merger, either by the conversion of securities issued pursuant to the
merger or the exercise of rights and warrants issued pursuant to the merger,
will not exceed the total number of shares of Cornerstone's common stock
outstanding immediately before the merger by more than 20%.

     Nevada's General Corporation Law requires the consent of the holders of a
majority of the shares of Cornerstone's common stock entitled to vote for a
sale, lease, or exchange of all of its property and assets.

DISSOLUTION OF EQUITY OFFICE OR CORNERSTONE; TERMINATION OF REIT STATUS

     Equity Office.  The Equity Office declaration of trust permits the
termination of the existence of Equity Office if approved by the affirmative
vote of the holders of not less two-thirds of the outstanding Equity Office
shares entitled to vote on the matter. In addition, the board of trustees may
terminate the status of Equity Office as a REIT under the Internal Revenue Code
for any taxable year without a vote of the holders of Equity Office common or
preferred shares.

     Cornerstone.  Under Nevada's General Corporation Law, Cornerstone may be
dissolved if its board of directors recommends dissolution to the stockholders
and holders of a majority of the shares of Cornerstone's outstanding common
stock entitled to vote approve such dissolution.

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BUSINESS COMBINATIONS WITH INTERESTED SHAREHOLDERS

     Equity Office.  The Maryland Business Combination Statute provides that,
unless exempted, a Maryland real estate investment trust may not engage in
business combinations, including mergers, dispositions of 10% or more of its
assets, issuances of shares and other specified transactions, with an
"interested shareholder" or its affiliates, for five years after the most recent
date on which the interested shareholder became an interested shareholder.
Thereafter, unless specified "price criteria" and other standards are met or an
exemption is available, a business combination with an interested shareholder or
its affiliates must be recommended by the board of trustees and approved by (a)
at least 80% of the outstanding voting shares and (b) at least two-thirds of the
outstanding voting shares, other than voting shares held by the interested
shareholder or any of its affiliates. Under the statute, an "interested
shareholder" generally is defined to mean a person or group which owns
beneficially, directly or indirectly, 10% of more of the outstanding voting
shares of the real estate investment trust. These requirements do not apply to a
business combination with an interested shareholder or its affiliates if
approved by the board of trustees before the time the interested shareholder
first became an interest shareholder.

     The Equity Office board of trustees has elected by resolution to exempt
form the provisions of the Maryland Business Combination Statute any business
combination with any person. However, this resolution, by its terms, may be
altered or repealed at any time, in whole or in part, by the board of trustees.

     Cornerstone.  Nevada's Business Combinations Act prohibits combinations
between a Nevada corporation and an interested stockholder of the corporation
for three years after the stockholder becomes interested unless the combination
or acquisition of shares by the interested stockholder on the date the
stockholder became an interested stockholder was approved by the corporation's
board of directors before that date. An interested stockholder is: (a) a person
who, directly or indirectly, has the ability to control the voting of 10% of the
voting stock of the corporation; or (b) an affiliate or associate of the
corporation who, at any time within three years before the date in question,
satisfied the definition in (a). A combination is broadly defined and includes
mergers, dispositions of 5% or more of its assets, issuances of shares and other
specified transactions.

     Although a Nevada corporation may, in its articles of incorporation, opt
out of the Business Combinations Act, Cornerstone has not done so.

CONTROL SHARE ACQUISITIONS

     Equity Office.  The Maryland Control Share Act provides that shares of a
Maryland real estate investment trust that are acquired in a "control share
acquisition," which is defined as the acquisition of shares comprising
one-fifth, one-third or a majority of all voting shares, have no voting rights
except:

     - if approved by shareholders by the affirmative vote of two-thirds of all
       the votes entitled to be cast on the matter, excluding all "interested
       shares;" or

     - if the acquisition of the shares has been approved or exempted at any
       time before the acquisition of the shares.

     The Maryland Control Share Act is applicable to a publicly traded Maryland
real estate investment trust unless its charter or bylaws specifically provides
that it shall be inapplicable.

     The Equity Office bylaws provide that the Maryland Control Share Act shall
not apply to any acquisition by any person of shares of Equity Office. Any
amendment to this provision by the board of trustees would require the approval
of shareholders by a vote of a majority of the votes cast. See "-- Amendment of
the Bylaws."

     Cornerstone.  Nevada's Control Shares Act restricts the voting rights of
shares of stock acquired by a stockholder of a Nevada corporation governed by
the act if the acquisition of such shares would provide such stockholder a
controlling interest in the corporation. A controlling interest is ownership of
one-fifth or more but less than one-third, one-third or more but less than a
majority, or a majority or more of the
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corporation's shares of stock entitled to vote generally in the election of
directors. Thus, the act applies to acquisitions of shares as a stockholder
moves from one level of control to the next. Only the shares acquired within 90
days immediately preceding the date when the stockholder acquires the relevant
controlling interest are subject to the limitation on voting rights.

     The Control Shares Act applies only to Nevada corporations (a) with 200 or
more stockholders of record, at least 100 of whom have addresses in Nevada
appearing in the corporation's stock ledger and (b) doing business in Nevada
directly or through an affiliated corporation. Cornerstone does not currently
have 100 stockholders of record who have addresses in Nevada appearing in
Cornerstone's stock ledger and Cornerstone does not do business in Nevada
directly or through an affiliated corporation. Moreover, the provisions of the
Control Shares Act do not apply to a Nevada corporation if the corporation's
articles of incorporation or bylaws in effect on the tenth day following the
acquisition of a controlling interest by a stockholder provide that such
provisions do not apply to the corporation or to an acquisition of a controlling
interest specifically by types of existing or future stockholders, whether or
not identified.

     Neither Cornerstone's bylaws nor its articles of incorporation contain such
an opt-out provision.

OTHER CONSTITUENCIES

     Equity Office.  Recent Maryland legislation expressly codifies the
authority of Maryland real estate investment trusts to include in their
declaration of trusts a provision that allows the board of trustees to consider
the effect of a potential acquisition of control on shareholders, employees,
suppliers, customers, creditors and communities in which offices or other
establishments of the trust are located. The Equity Office declaration of trust
does not include a provision of this type. The Maryland legislation also states,
however, that the inclusion or omission of such a provision in the declaration
of trust of a Maryland real estate investment trust allowing the board of
trustees to consider the effect of a potential acquisition of control on the
foregoing constituencies does not create an inference concerning factors that
may be considered by the board of trustees regarding a potential acquisition of
control.

     Cornerstone.  Nevada law contains a provision similar to the Maryland
legislation described above. The Nevada provision is discussed above under the
heading "-- Duties of Trustees and Directors."

DISSENTERS' RIGHTS

     Equity Office.  Maryland law applicable to Maryland real estate investment
trusts provides dissenters' rights for any shareholder who objects to a merger
to the same extent as a Maryland corporation's stockholders would enjoy such
rights. The shareholder has the right to demand and receive payment of the fair
value of his or her shares, unless:

     - the shares are listed on a national securities exchange or are designated
       as a national market security on the interdealer quotation system of the
       National Association of Securities Dealers, Inc. on the record date for
       determining shareholders entitled to vote on the merger; or

     - the shares are those of a successor entity, as long as the merger does
       not alter the contract rights of the shares as expressly set forth in the
       declaration of trust and the shares are converted in whole or in part in
       the merger into stock, including preferred stock, of the successor entity
       or cash, scrip, or other rights or interests arising out of the treatment
       of fractional shares.

     Cornerstone.  Nevada law regarding dissenter's rights is set forth in the
Merger Statute. Under the Merger Statute, a shareholder of a Nevada corporation
may dissent with respect to specified corporation actions and, as a result,
receive fair value for the stockholder's shares. Those actions to which
dissenter's rights apply are: (a) a merger of the corporation if shareholder
approval of the merger is required by the Merger Statute or the corporation's
articles of incorporation and the stockholder is entitled to vote thereon; (b)
merger of the corporation into a parent corporation that owns at least ninety
percent of each class of the outstanding shares of the corporation if the merger
is effected through section 92A.180 of the Nevada Revised Statutes; (c)
consummation of a plan of exchange in which the corporation's shares will be
acquired if the stockholder is entitled to vote thereon; and (d) other
transactions to which the
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corporation's articles of incorporation attach the right to dissent and obtain
fair payment for dissenter's shares.

     Dissenter's rights are not available, however, if the corporation is listed
on a national securities exchange, as Cornerstone is, unless (a) the
corporation's articles of incorporation provide otherwise or (b) the
stockholders are required under the plan of merger or exchange to accept
anything for their shares other than cash, stock or stock and cash in lieu of
fractional shares of stock of the surviving corporation or any other entity
whose stock was listed on a national securities exchange or NASDAQ or which had
at least 2,000 holders of record of such entity's stock, or any combination of
the above. As used in this paragraph, "stock" refers to shares of stock in a
corporation, membership in a nonprofit corporation, the interest of a member in
a limited-liability company or a beneficial owner of a business trust, or the
partnership interest of a partner in a general or limited partnership.

DISTRIBUTIONS

     Equity Office.  The Equity Office declaration of trust provides that the
trustees will endeavor to declare and pay distributions as necessary for Equity
Office to qualify as a REIT under the Internal Revenue Code. However,
shareholders do not have any right to a distribution unless and until authorized
and declared by the board of trustees. Distributions may not be paid on the
Equity Office common shares unless all accrued but unpaid distributions on each
outstanding series of preferred shares of Equity Office have been declared and
paid or set apart for payment. Payments of distributions by Equity Office are
not limited by any rules concerning the capital or surplus of Equity Office or
the par value of the Equity Office shares.

     Cornerstone.  Nevada's General Corporation Law provides that the board of
directors may not make a distribution of money or property to its stockholders
if such distribution would prevent the corporation from paying its debts as they
became due in the ordinary course of business or, unless and to the extent
specifically allowed by the corporation's articles of incorporation, if after
the distribution, the corporation's total assets would be less than the sum of
its total liabilities plus that amount that would be needed, if the corporation
were to be dissolved at the time of the distribution, to satisfy the
preferential rights to distributions upon dissolution of the corporation's
shareholders whose rights upon dissolution are superior to those receiving the
distribution.

REIT OWNERSHIP LIMITATIONS

     Equity Office.  For Equity Office to qualify as a REIT under the Internal
Revenue Code, no more than 50% in value of its outstanding shares of beneficial
interest may be owned, actually or constructively, by five or fewer
"individuals," which, as defined in the Internal Revenue Code for this purpose,
includes certain entities. In addition, if Equity Office, or an actual or
constructive owner of 10% or more of the shares of Equity Office, owns, actually
or constructively, 10% or more of a tenant of Equity Office, then the rent
received by Equity Office from that tenant will not be qualifying income for
purposes of determining whether Equity Office meets the requirements for
qualification as a REIT under the Internal Revenue Code. A REIT's shares also
must be beneficially owned by 100 or more persons.

     As a means of addressing these requirements, the Equity Office declaration
of trust provides that, subject to exceptions, no person may own, or be deemed
to own directly and/or by virtue of the attribution provisions of the Internal
Revenue Code, more than 9.9%, in value or number of shares, whichever is more
restrictive, of the issued and outstanding shares of any class or series of
shares. Under the Equity Office declaration of trust, the board of trustees may
increase the ownership limit with respect to any class or series of shares.
However, after giving effect to this increase, five beneficial owners of common
shares may not beneficially own in the aggregate more than 49.5% of the
outstanding common shares. In addition, the Equity Office board of trustees is
required to waive or modify the ownership limit with respect to one or more
persons who would not be treated as "individuals" under the Internal Revenue
Code if such person submits to the Equity Office board of trustees specified
information that demonstrates, to the reasonable satisfaction of the board of
trustees, that such ownership would not jeopardize Equity Office's status as a

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REIT under the Internal Revenue Code. The Equity Office declaration of trust
further prohibits any person from transferring any Equity Office common or
preferred shares if the transfer would result in shares of beneficial interest
of Equity Office being owned by fewer than 100 persons or otherwise would cause
Equity Office not to qualify as a REIT.

     If any transfer of shares or any other event would otherwise result in any
person violating the ownership limits, then the declaration of trust provides
that (a) the transfer will be void and of no force or effect with respect to the
prohibited transferee with respect to that number of shares that exceeds the
ownership limits and (b) the prohibited transferee would not acquire any right
or interest in the shares. The shares transferred in violation of the ownership
limit instead would be transferred automatically to a charitable trust, the
beneficiary of which would be a qualified charitable organization selected by
Equity Office.

     The trustee of the charitable trust would be required to sell the shares
transferred in violation of the ownership limit to a person or entity who could
own the shares without violating the ownership limit, and to distribute to the
prohibited transferee an amount equal to the lesser of the price paid by such
person for the shares transferred in violation of the ownership limit or the
sales proceeds received by the charitable trust for the shares. In the case of a
transfer for no consideration, such as a gift, the charitable trustee would be
required to sell the shares to a qualified person or entity and distribute to
the prohibited transferee an amount equal to the lesser of the fair market value
of the shares as of the date of the prohibited transfer or the sales proceeds
received by the charitable trust.

     Under its declaration of trust, Equity Office, or its designee, would have
the right to purchase the shares from the charitable trust at a price per share
equal to the lesser of (a) the price per share in the transaction that resulted
in the transfer of the shares to the charitable trust, or, in the case of a
devise or gift, the market price at the time of such devise or gift, and (b) the
market price of such shares on the date Equity Office, or its designee, were to
agree to purchase the shares. Any proceeds derived from the sale of the shares
in excess of the amount distributed to the prohibited transferee under these
provisions would be distributed to the beneficiary of the charitable trust.

     The charitable trustee will have the sole right to vote the shares that it
holds, and any distributions paid on shares held by the charitable trustee would
be paid to the beneficiary of the charitable trust.

     If the transfer to the charitable trust of the shares that were transferred
in violation of the ownership limit is not automatically effective for any
reason, then the transfer to that resulted in the violation of the ownership
limit would be void.

     All persons or entities who own, directly or by virtue of the attribution
provisions of the Internal Revenue Code, more than 5%, or such other percentage
between 1/2 of 1% and 5% as provided in applicable rules and regulations under
the Internal Revenue Code, of the lesser of the number or value of the
outstanding Equity Office shares must give a written notice to Equity Office by
January 30 of each year stating the name and address of such owner, the number
of Equity Office shares owned and a description of the manner in which such
Equity Office shares are held. In addition, a holder of record of Equity Office
shares subject to the foregoing requirement who holds its Equity Office shares
as nominee for another person or entity which is required to include in gross
income the dividends received on such shares must also give notice of the name
and address of such person or entity and the number of Equity Office shares of
such person or entity with respect to which such holder of record is nominee. In
addition, each record, beneficial and constructive holder of Equity Office
shares is required, upon demand of Equity Office, to disclose to Equity Office
in writing any information with respect to the direct, indirect and constructive
ownership of Equity Office shares as the Equity Office board of trustees deems
necessary to comply with the provisions of the Internal Revenue Code applicable
to REITs, to comply with the requirements of any taxing authority or
governmental agency or to determine any such compliance.

     As part of the REIT merger, the Equity Office declaration of trust will be
amended to add an additional limitation on the ownership by non-U.S. persons of
Equity Office common shares and preferred shares issued by Equity Office in the
future. This additional limitation would result in adverse

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consequences for a non-U.S. person whose purchase of Equity Office common shares
or any preferred shares of Equity Office issued in the future caused the foreign
ownership limit to be exceeded and, therefore, may deter additional purchases of
Equity Office shares by non-U.S. persons.

     The foregoing restrictions on ownership and transferability would not apply
if the Equity Office board of trustees were to determine that it is no longer in
the best interests of Equity Office to attempt to qualify, or to continue to
qualify, as a REIT under the Internal Revenue Code.

     Cornerstone.  To help ensure that Cornerstone continues to qualify as a
REIT, Article 8 of Cornerstone's articles of incorporation provides that shares
of Cornerstone's capital stock shall not be transferred to any person if such
transfer would cause such person to become the direct or indirect owner of more
than 6% of the value of the outstanding shares of Cornerstone's capital stock.
Shares of stock acquired in excess of this ownership limit shall be deemed to be
transferred to Cornerstone as trustee for the benefit of the person to whom the
person who acquired the excess shares later transfers such shares. In addition,
excess shares shall be deemed to have been offered for sale to Cornerstone or
its designee at their "fair market value" for a 90-day period. Article 8 further
provides that a person who knowingly violates the ownership limit must indemnify
Cornerstone and its stockholders for losses if such violation causes Cornerstone
either to fail to qualify as a REIT or to be subject to personal holding company
taxes. The affirmative vote of the holders of at least 80% of the outstanding
shares of Cornerstone common stock is required to alter, amend, repeal or adopt
any provision inconsistent with such restrictions.

     Cornerstone's articles of incorporation also contain provisions designed to
assist it in becoming a "domestically controlled REIT" under the Internal
Revenue Code. Article 9 of Cornerstone's articles of incorporation provides that
shares of Cornerstone's stock may not be transferred to any non-U.S. person if
such transfer would cause such non-U.S. person to become the direct or indirect
owner of more than 3% of the value of the outstanding shares of any class of
capital stock of Cornerstone. Shares of stock acquired in excess of the non-U.S.
ownership limit are deemed to be transferred to Cornerstone as trustee for the
benefit of the person to whom the non-U.S. person who acquired the excess shares
later transfers such shares. In addition, excess shares are deemed to have been
offered for sale to Cornerstone or its designee at their "fair market value" for
a 90-day period. Article 9 does not apply, however, to transfers by any U.S.
person by operation of law or pursuant to death, a merger or sale of
substantially all of the assets of such person, bankruptcy or pledges of
security.

     As used in the preceding paragraph:  "non-U.S. person" means (a) a
nonresident alien individual, as defined in the Internal Revenue Code, (b) a
foreign corporation, foreign partnership, foreign trust, foreign estate, foreign
government, and any other organization or entity which is not organized under
the laws of the United States or a State, and (c) any other person or entity
treated as a "foreign person" under regulations promulgated under the Internal
Revenue Code. "U.S. person" means any person other than a non-U.S. person.

                                 LEGAL MATTERS

     The validity of the EOP Partnership units and the Equity Office common
shares offered by this consent solicitation/information statement/prospectus
will be passed upon for EOP Partnership and Equity Office by Hogan & Hartson
L.L.P., Washington, D.C. and New York, NY.

     The qualification of the REIT merger as a reorganization under section
368(a) of the Internal Revenue Code, and the qualification of Equity Office as a
REIT and the classification of EOP Partnership as a partnership for federal
income tax purposes will be passed upon for Equity Office and EOP Partnership by
Hogan & Hartson L.L.P., Washington, D.C. and New York, NY, counsel for Equity
Office.

     The validity of the shares of Cornerstone common stock offered by this
consent solicitation/ information statement/prospectus will be passed upon for
Cornerstone by Lionel, Sawyer & Collins, Las Vegas, Nevada.

                                       161
<PAGE>   174


     The qualification of the REIT merger as a reorganization under section
368(a) of the Internal Revenue Code, and the qualification of Cornerstone as a
REIT and the classification of Cornerstone Partnership as a partnership for
federal income tax purposes will be passed upon for Cornerstone and Cornerstone
Partnership by King & Spalding, Atlanta, Georgia and New York, New York, counsel
for Cornerstone.

                                    EXPERTS

     Ernst & Young LLP, independent auditors, have audited the consolidated
financial statements and schedule of Equity Office included in Equity Office's
Annual Report on Form 10-K for the year ended December 31, 1999, and have
audited the consolidated financial statements and schedule included in EOP
Partnership's Annual Report on Form 10-K for the year ended December 31, 1999,
as set forth in their reports, which are incorporated by reference in this
consent solicitation/information statement/prospectus and elsewhere in the
registration statement. The Equity Office and EOP Partnership consolidated
financial statements and schedules are incorporated by reference in reliance on
Ernst & Young LLP's reports, given on their authority as experts in accounting
and auditing.

     The consolidated financial statements of Cornerstone incorporated in this
consent solicitation/ information statement/prospectus by reference to the
Annual Report on Form 10-K for the year ended December 31, 1999, and the
consolidated financial statements of the Cornerstone Partnership included in
this consent solicitation/information statement/prospectus for the year ended
December 31, 1999, have been so incorporated or included in reliance on the
reports of PricewaterhouseCoopers LLP, independent accountants, given on the
authority of said firm as experts in auditing and accounting.

                                       162
<PAGE>   175


                      WHERE YOU CAN FIND MORE INFORMATION

     Equity Office, EOP Partnership and Cornerstone have filed with the SEC a
registration statement on Form S-4 (333-               ), of which this consent
solicitation/information statement/prospectus forms a part. The registration
statement registers (a) the distribution to Cornerstone Partnership unitholders
of the EOP partnership units to be issued in the partnership merger, which are
redeemable by the unitholder for cash or, at the election of Equity Office,
Equity Office common shares, and (b) the distribution of shares of common stock
of Cornerstone to Cornerstone Partnership unitholders who elect to redeem their
Cornerstone Partnership units for Cornerstone common stock prior to the merger
and in connection with the REIT merger. The registration statement, including
the attached exhibits and schedules, contains additional relevant information
about EOP Partnership units. The rules and regulations of the SEC allow Equity
Office, EOP Partnership and Cornerstone to omit certain information included in
the registration statement from this consent solicitation/information
statement/prospectus. In addition, Equity Office, EOP Partnership and
Cornerstone file reports, proxy statements and other information with the SEC
under the Securities Exchange Act of 1934. You may read and copy any of this
information at the following locations of the SEC:

Public Reference Room
450 Fifth Street, N.W.
Room 1024
Washington, D.C. 20549
New York Regional Office
7 World Trade Center
Suite 1300
New York, NY 10048
Chicago Regional Office
Citicorp Center
500 West Madison Street
Suite 1400
Chicago, IL 60661- 2511

     You may obtain information on the operation of the SEC's Public Reference
Room by calling the SEC at 1-800-SEC-0330.

     The SEC also maintains an Internet web site that contains reports, proxy
statements and other information regarding issuers, including Equity Office, EOP
Partnership and Cornerstone, who file electronically with the SEC. The address
of that site is http://www.sec.gov. Reports, proxy statements and other
information concerning Equity Office and Cornerstone may also be inspected at
the offices of the New York Stock Exchange, which are located at 20 Broad
Street, New York, New York 10005.

     The SEC allows Equity Office, EOP Partnership and Cornerstone to
"incorporate by reference" information in this document, which means that they
can disclose important information to you by referring you to another document
filed separately with the SEC. The information incorporated by reference is
considered to be a part of this consent solicitation/information
statement/prospectus, except for any information that is superseded by
information included directly in this document.

     The documents listed below that Equity Office, EOP Partnership and
Cornerstone have previously filed with the SEC are considered to be a part of
this consent solicitation/information statement/ prospectus. They contain
important information about these companies and their financial condition.

EQUITY OFFICE SEC FILINGS (FILE NO. 1-13115):

<TABLE>
<S>                                            <C>
Annual Report on Form 10-K...................  Year Ended December 31, 1999
Current Report on Form 8-K...................  Filed on February 16, 2000
Registration Statement on Form 8-A...........  Filed on June 19, 1997, setting forth the
                                               description of Equity Office common shares
</TABLE>

EOP PARTNERSHIP SEC FILINGS (FILE NO. 1-13625):

<TABLE>
<S>                                            <C>
Annual Report on Form 10-K...................  Year Ended December 31, 1999
Current Reports on Form 8-K..................  Filed on March 24, 2000, March 15, 2000 and
                                               February 16, 2000
</TABLE>

                                       163
<PAGE>   176


CORNERSTONE SEC FILINGS (FILE NO. 1-12861):

<TABLE>
<S>                                            <C>
Annual Report on Form 10-K...................  Year Ended December 31, 1999
Current Reports on Form 8-K..................  Filed on April 10, 2000, March 10, 2000 and
                                               February 16, 2000, as amended
Registration Statement on Form 8-A...........  Filed on March 11, 1997, setting forth the
                                               description of Cornerstone common stock
</TABLE>

     Equity Office, EOP Partnership and Cornerstone incorporate by reference
additional documents that they may file with the SEC between the date of this
consent solicitation/information statement/prospectus and the date of the
special meetings of Equity Office and Cornerstone in connection with the REIT
merger. These include periodic reports, such as Annual Reports on Form 10-K,
Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as proxy
materials.

     If you are a shareholder of Equity Office, a unitholder of EOP Partnership
or a unitholder of Cornerstone Partnership, Equity Office, EOP Partnership or
Cornerstone, as the case may be, may have sent to you some of the documents
incorporated by reference in this document, but you can obtain any of them
through Equity Office, EOP Partnership or Cornerstone, as the case may be, or
through the SEC or the SEC's web site described above. Documents incorporated by
reference are available from Equity Office, including EOP Partnership and
Cornerstone, as applicable, without charge, excluding all exhibits unless
specifically incorporated by reference as an exhibit to this document.
Shareholders of Equity Office, holders of EOP Partnership units or stockholders
of Cornerstone may obtain documents incorporated by reference in this document
by requesting them from writing or by telephone from the appropriate company at
the following addresses:

          EQUITY OFFICE PROPERTIES TRUST or
        EOP OPERATING LIMITED PARTNERSHIP
        Two North Riverside Plaza
        Suite 2100
        Chicago, Illinois 60606
        Attention: Stanley M. Stevens
        Telephone: (312) 466-3300
        CORNERSTONE PROPERTIES INC.
        Tower 56
        126 East 56th Street, 6th Floor
        New York, New York 10022
        Attention: Thomas P. Loftus
        Telephone: (212) 605-7131

     IF YOU WOULD LIKE TO REQUEST DOCUMENTS, PLEASE DO SO BY             , 2000
IN ORDER TO RECEIVE TIMELY DELIVERY OF SUCH DOCUMENTS. If you request any
incorporated documents, we will mail them to you by first class mail, or another
equally prompt means, within one business day after we receive your request.

     Equity Office has supplied all information contained or incorporated by
reference in this consent solicitation/information statement/prospectus relating
to Equity Office and EOP Partnership, and Cornerstone has supplied all such
information relating to Cornerstone and Cornerstone Partnership. This document
constitutes the prospectus of Equity Office and EOP Partnership, the information
statement of EOP Partnership, the prospectus of Cornerstone and the consent
solicitation of Cornerstone Partnership.

                                       164
<PAGE>   177

                      WHAT INFORMATION YOU SHOULD RELY ON

     NO PERSON HAS BEEN AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY
REPRESENTATION THAT DIFFERS FROM, OR ADDS TO, THE INFORMATION DISCUSSED IN THIS
CONSENT SOLICITATION/INFORMATION STATEMENT/PROSPECTUS OR IN THE ANNEXES ATTACHED
HERETO WHICH ARE SPECIFICALLY INCORPORATED BY REFERENCE. THEREFORE, IF ANYONE
GIVES YOU DIFFERENT OR ADDITIONAL INFORMATION, YOU SHOULD NOT RELY ON IT.

     THIS DOCUMENT IS DATED             , 2000. THE INFORMATION CONTAINED IN
THIS CONSENT SOLICITATION/INFORMATION STATEMENT/PROSPECTUS SPEAKS ONLY AS OF ITS
DATE UNLESS THE INFORMATION SPECIFICALLY INDICATES THAT ANOTHER DATE APPLIES.
THIS CONSENT SOLICITATION/INFORMATION STATEMENT/PROSPECTUS DOES NOT CONSTITUTE
AN OFFER TO EXCHANGE OR SELL, OR A SOLICITATION OF AN OFFER TO EXCHANGE OR
PURCHASE, EOP PARTNERSHIP UNITS, EQUITY OFFICE COMMON SHARES, CORNERSTONE
PARTNERSHIP UNITS OR CORNERSTONE COMMON STOCK OR TO SOLICIT CONSENTS, TO OR FROM
ANY PERSON TO WHOM IT IS UNLAWFUL TO DIRECT THESE ACTIVITIES.

                                       165
<PAGE>   178

                         INDEX TO FINANCIAL STATEMENTS

<TABLE>
<S>                                                           <C>
EOP Partnership Pro Forma Condensed Combined Financial
  Statements................................................   F-2
  EOP Partnership Pro Forma Condensed Combined Balance
     Sheet..................................................   F-3
  EOP Partnership Pro Forma Condensed Combined Statement of
     Operations.............................................   F-4
  EOP Partnership Notes to Pro Forma Condensed Combined
     Financial Statements...................................   F-5
Equity Office Pro Forma Condensed Combined Financial
  Statements................................................  F-10
  Equity Office Pro Forma Condensed Combined Balance
     Sheet..................................................  F-11
  Equity Office Pro Forma Condensed Combined Statement of
     Operations.............................................  F-12
  Equity Office Notes to Pro Forma Condensed Combined
     Financial Statements...................................  F-13
Cornerstone Partnership Historical Consolidated Financial
  Statements:
  Report of Independent Accountants.........................  F-19
  Cornerstone Partnership Consolidated Balance Sheets.......  F-20
  Cornerstone Partnership Consolidated Statements of
     Income.................................................  F-21
  Cornerstone Partnership Consolidated Statements of
     Comprehensive Income...................................  F-22
  Cornerstone Partnership Consolidated Statements of
     Partners' Capital......................................  F-23
  Cornerstone Partnership Consolidated Statements of Cash
     Flows..................................................  F-24
  Cornerstone Partnership Notes to Consolidated Financial
     Statements.............................................  F-25
Cornerstone Partnership Historical Consolidated Financial
  Statement Schedule:
     Schedule III...........................................  F-47
</TABLE>

                                       F-1
<PAGE>   179

                       EOP OPERATING LIMITED PARTNERSHIP

               PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS
                 AS OF AND FOR THE YEAR ENDED DECEMBER 31, 1999
                                  (UNAUDITED)

     The accompanying Unaudited Pro Forma Condensed Combined Balance Sheet as of
December 31, 1999 reflects the following transactions as if they had occurred on
December 31, 1999:

     - the proposed merger of EOP Partnership and Cornerstone Partnership; and

     - the issuance of $500 million of unsecured notes on March 21, 2000, due
       March 2006, coupon rate of 8.4% per annum and effective rate of 8.5% per
       annum.

     The accompanying Unaudited Pro Forma Condensed Combined Statement of
Operations for the year ended December 31, 1999 reflects the following
transactions as if they had occurred on January 1, 1999:

     - the proposed merger of EOP Partnership and Cornerstone Partnership; and

     - the issuance of $500 million of unsecured notes on March 21, 2000, due
       March 2006, coupon rate of 8.4% per annum and effective rate of 8.5% per
       annum.

     In the opinion of management, all significant adjustments necessary to
reflect the effects of the partnership merger have been made.

                                       F-2
<PAGE>   180

                       EOP OPERATING LIMITED PARTNERSHIP

                   PRO FORMA CONDENSED COMBINED BALANCE SHEET
                         DECEMBER 31, 1999 (UNAUDITED)
                             (DOLLARS IN THOUSANDS)

<TABLE>
<CAPTION>
                                                         CORNERSTONE
                                  EOP OPERATING          PROPERTIES          MERGER AND         EOP OPERATING
                               LIMITED PARTNERSHIP   LIMITED PARTNERSHIP        OTHER        LIMITED PARTNERSHIP
                                   HISTORICAL            HISTORICAL        ADJUSTMENTS (A)        PRO FORMA
                               -------------------   -------------------   ---------------   -------------------
<S>                            <C>                   <C>                   <C>               <C>
ASSETS:
Investment in real estate,
  net........................      $12,572,153           $3,565,637          $  710,997(B)       $16,848,787
Cash and cash equivalents....            2,338               19,679                  --(C)            22,017
Rent and other receivables...          193,194               91,968             (77,243)(D)          207,919
Escrow deposits and
  restricted cash............           19,754              222,043                  --              241,797
Investment in unconsolidated
  joint ventures.............          865,863               31,725               8,275(B)           905,863
Prepaid expenses and other
  assets.....................          392,756              239,176            (199,275)(E)          432,657
                                   -----------           ----------          ----------          -----------
TOTAL ASSETS.................      $14,046,058           $4,170,228          $  442,754          $18,659,040
                                   ===========           ==========          ==========          ===========
LIABILITIES AND PARTNERS'
  CAPITAL:
Mortgage debt................      $ 1,743,871           $1,435,405          $  (27,326)(F)      $ 3,151,950
Unsecured notes..............        3,655,047                   --             499,320(G)         4,154,367
Lines of credit..............          453,000              329,000             691,027(H)         1,473,027
Distribution payable.........            5,446                   --                  --                5,446
Other liabilities............          479,167              113,240                  65(I)           592,472
                                   -----------           ----------          ----------          -----------
TOTAL LIABILITIES............        6,336,531            1,877,645           1,163,086            9,377,262
                                   -----------           ----------          ----------          -----------
Minority interest in
  partially owned
  properties.................           39,027               22,532                  --               61,559
                                   -----------           ----------          ----------          -----------
Preferred shares.............          615,000               50,000             (50,000)(J)          615,000
Partners' capital............        7,055,500            2,220,051            (670,332)(K)        8,605,219
                                   -----------           ----------          ----------          -----------
TOTAL PARTNERS' CAPITAL......        7,670,500            2,270,051            (720,332)           9,220,219
                                   -----------           ----------          ----------          -----------
TOTAL LIABILITIES AND
  PARTNERS' CAPITAL..........      $14,046,058           $4,170,228          $  442,754          $18,659,040
                                   ===========           ==========          ==========          ===========
</TABLE>

                                       F-3
<PAGE>   181

                       EOP OPERATING LIMITED PARTNERSHIP

              PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS
                FOR THE YEAR ENDED DECEMBER 31, 1999 (UNAUDITED)
                  (DOLLARS IN THOUSANDS, EXCEPT PER UNIT DATA)

<TABLE>
<CAPTION>
                                                                CORNERSTONE                         EOP
                                                  EOP           PROPERTIES      MERGER       OPERATING LIMITED
                                           OPERATING LIMITED      LIMITED      AND OTHER        PARTNERSHIP
                                              PARTNERSHIP       PARTNERSHIP   ADJUSTMENTS        PRO FORMA
                                           -----------------    -----------   -----------    -----------------
                                                                                  (A)
<S>                                        <C>                  <C>           <C>            <C>
REVENUES:
  Rental.................................    $  1,493,196        $455,204      $  6,181(L)     $  1,954,581
  Tenant reimbursements..................         281,358         121,385            --             402,743
  Parking................................         112,204          27,343            --             139,547
  Other..................................          32,298           4,598            --              36,896
  Fee income.............................           8,939           2,677            --              11,616
  Interest/dividends.....................          14,248           4,211            --              18,459
                                             ------------        --------      --------        ------------
      Total revenues.....................       1,942,243         615,418         6,181           2,563,842
                                             ------------        --------      --------        ------------
EXPENSES:
  Interest:
    Expense incurred.....................         413,995         135,009        90,855(M)          639,859
    Amortization of deferred financing
      costs..............................           4,693           2,004         3,669(N)           10,366
  Depreciation...........................         339,751          87,971        15,109(O)          442,831
  Amortization...........................          14,545           8,755        (8,755)(P)          14,545
  Real estate taxes......................         243,778          71,554            --             315,332
  Insurance..............................           9,589           3,548            --              13,137
  Repairs and maintenance................         209,630          74,728            --             284,358
  Property operating.....................         199,879          52,947            --             252,826
  Ground rent............................           6,887           1,407            --               8,294
  General and administrative.............          80,927          27,006            --(Q)          107,933
                                             ------------        --------      --------        ------------
      Total expenses.....................       1,523,674         464,929       100,878           2,089,481
                                             ------------        --------      --------        ------------
Income before allocation to minority
  interests, income from investment in
  unconsolidated joint ventures and net
  gain on sales of real estate...........         418,569         150,489       (94,697)            474,361
Minority interests -- partially owned
  properties.............................          (1,981)         (5,755)           --              (7,736)
Income from investment in unconsolidated
  joint ventures.........................          13,824             898          (176)(R)          14,546
Net gain on sales of real estate.........          59,661         131,034            --             190,695
                                             ------------        --------      --------        ------------
Net income from continuing operations....         490,073         276,666       (94,873)            671,866
Put option settlement....................          (5,658)             --            --              (5,658)
Preferred distributions..................         (43,603)         (3,500)        3,500(S)          (43,603)
                                             ------------        --------      --------        ------------
Net income from continuing operations
  before extraordinary items and
  cumulative effect of a change in
  accounting principle available for
  units..................................    $    440,812        $273,166      $(91,373)       $    622,605
                                             ============        ========      ========        ============
Net income from continuing operations
  before extraordinary items and
  cumulative effect of a change in
  accounting principle per weighted
  average unit outstanding -- basic......    $       1.53(T)                                   $       1.77(T)
                                             ============                                      ============
Weighted average units
  outstanding -- basic...................     288,326,547                                       351,114,475
                                             ============                                      ============
Net income from continuing operations
  before extraordinary items and
  cumulative effect of a change in
  accounting principle per weighted
  average unit outstanding -- diluted....    $       1.51(T)                                   $       1.76(T)
                                             ============                                      ============
Weighted average units outstanding --
  diluted................................     291,157,204                                       354,965,413
                                             ============                                      ============
</TABLE>

                                       F-4
<PAGE>   182


                       EOP OPERATING LIMITED PARTNERSHIP
           NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS
                         DECEMBER 31, 1999 (UNAUDITED)
                    (DOLLARS IN THOUSANDS, EXCEPT PER UNIT)

(A) Represents adjustments to record the merger between EOP Partnership and
    Cornerstone Partnership based upon the assumed purchase price of $4.6
    billion assuming a value of $24.6818 per unit of EOP Partnership's units and
    adjustments to record the issuance of $500 million in unsecured notes which
    occurred on March 21, 2000. The calculation of the merger acquisition cost
    is as follows:

<TABLE>
          <S>                                                          <C>          <C>
          Issuance of 62.8 million EOP Partnership units based on a .7009
          exchange rate in exchange for 89.6 million Cornerstone Partnership
          units..................................................................   $1,549,719
          Cash portion of merger consideration:
               Cornerstone Partnership units (58,551,525 @ $18.00)...   1,053,927
               Cornerstone preferred units (3,030,303 @ $18.00)......      54,545    1,108,472
                                                                       ----------
          EOP Partnership's current ownership of 250,700 shares of Cornerstone
            common stock.........................................................        3,480
          Assumption of Cornerstone Partnership's total liabilities..............    1,877,645
          Assumption of the convertible promissory note and related accrued
            interest payable owed by Cornerstone Properties, Inc to be assumed by
            EOP Partnership in the merger (see Notes F and I)....................       12,991
          Adjustment to Cornerstone Partnership's mortgage debt to reflect market
            value (see Note F)...................................................      (40,252)
          Cornerstone Partnership's minority interest allocation for partially
            owned properties.....................................................       22,532
          Merger costs (see calculation below)...................................       78,000
                                                                                    ----------
                    Total merger acquisition cost................................   $4,612,587
                                                                                    ==========
</TABLE>

     The following is a calculation of the EOP Partnership units to be issued in
the merger:

<TABLE>
<CAPTION>
                                                                           UNITS
                                                                        -----------
          <S>                                                           <C>
          Cornerstone Partnership units outstanding at December 31,
            1999......................................................  148,384,088
          Less Cornerstone Partnership units redeemed for cash........  (58,551,525)
          Less EOP Partnership's current ownership of 250,700 shares
            of Cornerstone common stock...............................     (250,700)
                                                                        -----------
          Cornerstone Partnership units to be converted in the merger
            into EOP Partnership units at an exchange rate of .7009...   89,581,863
                                                                        ===========
          EOP Partnership units to be issued in the merger............   62,787,928
          EOP Partnership units outstanding at December 31, 1999......  285,786,346
                                                                        -----------
            EOP Partnership units outstanding after the merger........  348,574,274
                                                                        ===========
</TABLE>

     The following is a calculation of estimated merger costs:

<TABLE>
          <S>                                                           <C>
          Employee termination costs..................................  $    43,800
          Investment advisory fees....................................       15,000
          Transfer taxes..............................................       10,000
          Legal, accounting and other fees............................        7,700
          Loan assumption fees........................................        1,500
                                                                        -----------
                    Total merger costs................................  $    78,000
                                                                        ===========
</TABLE>

                                       F-5
<PAGE>   183
                       EOP OPERATING LIMITED PARTNERSHIP
   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

(B)  Represents the estimated increase in Cornerstone Partnership's investment
     in real estate based upon the merger acquisition cost to reflect the
     allocation to other tangible assets of Cornerstone Partnership being
     acquired:

<TABLE>
          <S>                                                           <C>
          Merger acquisition cost (see Note A)........................  $4,612,587
                                                                        ----------
          Less basis of Cornerstone Partnership's net assets acquired:
               Investment in real estate, net.........................   3,565,637
               Cash and cash equivalents..............................      19,679
               Rent and other receivables (excluding $77.2 million of
                deferred rents receivable)............................      14,725
               Escrow deposits and restricted cash....................     222,043
               Investment in unconsolidated joint ventures............      31,725
               Prepaid expenses and other assets (excluding $199.7
                million of deferred leasing, financing and other costs
                (see Note E)).........................................      39,506
                                                                        ----------
                    Subtotal..........................................   3,893,315
                                                                        ----------
          Adjustment to record fair value of Cornerstone Partnership's
            investment in real estate and investment in unconsolidated
            joint ventures, net.......................................     719,272
          Less adjustment allocated to investment in unconsolidated
            joint ventures............................................      (8,275)
                                                                        ----------
          Adjustment allocated to investment in real estate...........  $  710,997
                                                                        ==========
</TABLE>

(C) There was no change in cash and cash equivalents as a result of the
    following transactions:

<TABLE>
          <S>                                                           <C>
          Anticipated borrowings on additional credit facilities to
            finance the cash portion of the merger (see Note H).......  $   691,027
          Gross proceeds from the $500 million unsecured notes
            offering (see Note G).....................................      500,000
          Less cash portion of merger consideration (see Note A)......   (1,108,472)
          Less merger costs (see Note A)..............................      (78,000)
          Less financing costs related to the $500 million unsecured
            notes offering (see Note E)...............................       (3,875)
          Less discount on the $500 million unsecured notes offering
            (see Note G)..............................................         (680)
                                                                        -----------
               Net adjustment to cash and cash equivalents............  $        --
                                                                        ===========
</TABLE>

(D) Represents the elimination of Cornerstone Partnership's deferred rents
    receivable of $77.2 million which arose from the historical straight-lining
    of rental revenue.

(E) Represents an adjustment for the following:

<TABLE>
          <S>                                                           <C>
          Cornerstone Partnership's deferred leasing, financing and
            other costs which were not assigned any value in the
            allocation of the merger acquisition cost.................  $(199,670)
          Transfer of EOP Partnership's current ownership of 250,700
            shares of Cornerstone common stock to merger acquisition
            cost (see Note A).........................................     (3,480)
          Additional deferred financing costs associated with the $500
            million unsecured note offering...........................      3,875
                                                                        ---------
                    Total.............................................  $(199,275)
                                                                        =========
</TABLE>

                                       F-6
<PAGE>   184
                       EOP OPERATING LIMITED PARTNERSHIP
   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

(F)  To reflect the following:

<TABLE>
          <S>                                                           <C>
          Adjustment to Cornerstone Partnership's mortgage debt to
            reflect market value (see Note F).........................  $(40,252)
          Assumption of the convertible promissory note and related
            accrued interest payable from Cornerstone Properties, Inc.
            to be assumed by EOP Partnership in the merger............    12,926
                                                                        --------
                                                                        $(27,326)
                                                                        ========
</TABLE>

(G) To reflect the $500 million unsecured notes offering net of a $.7 million
    discount.

(H) To reflect borrowings on additional credit facilities to finance the cash
    portion of the merger as follows:

<TABLE>
          <S>                                                           <C>
          Cash portion of merger consideration (See Note A)...........  $1,108,472
          Merger costs (See Note A)...................................      78,000
          Less net proceeds from the $500 million unsecured notes
            offering (see Note C).....................................    (495,445)
                                                                        ----------
                    Borrowings on additional credit facilities........  $  691,027
                                                                        ==========
</TABLE>

(I)  To reflect the assumption of the accrued interest payable related to the
     convertible promissory note owed by Cornerstone's Properties, Inc to be
     assumed by EOP Partnership in the merger.

(J)  To record the redemption of Cornerstone's preferred units into cash (see
     Note A).

(K) To reflect the net decrease in partners' capital associated with the merger
    as follows:

<TABLE>
          <S>                                                           <C>
          Issuance of 62.8 million EOP Partnership units based on the
            exchange rate, in exchange for 89.6 million Cornerstone
            Partnership units.........................................  $ 1,549,719
          Less total pre-merger pro forma partners' capital of
            Cornerstone Partnership...................................   (2,220,051)
                                                                        -----------
                    Net decrease to partners' capital.................  $  (670,332)
                                                                        ===========
</TABLE>

(L)  To reflect the adjustment for the straight-line effect of scheduled rent
     increases.

(M) To reflect the additional interest expense incurred from the $500 million
    unsecured notes offering and borrowings from additional credit facilities to
    finance the cash portion of the merger.

<TABLE>
          <S>                                                           <C>
          Additional borrowings from $500 million unsecured notes
            offering (see Note G) and credit facilities (see Note
            H)........................................................  $1,190,347
          Weighted average interest rate..............................        7.57%
                                                                        ----------
          Additional interest expense.................................      90,109
          Interest expense on the convertible promissory note from
            Cornerstone's Properties, Inc. that will be assumed by EOP
            Partnership in the merger.................................         746
                                                                        ----------
                                                                        $   90,855
                                                                        ==========
</TABLE>

<TABLE>
<S>  <C>                                                           <C>
(N)  To reflect the amortization of $3.9 million of financing
       costs incurred with the $500 million unsecured notes
       offering over the six-year term...........................   $  646
     To reflect additional amortization of the adjustment to
       Cornerstone Partnership's mortgage debt to market value...    3,023
                                                                    ------
                                                                    $3,669
                                                                    ======
</TABLE>

                                       F-7
<PAGE>   185
                       EOP OPERATING LIMITED PARTNERSHIP
   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

(O) To reflect additional depreciation expense related to the adjustment to the
    investment in real estate on a straight-line basis.

<TABLE>
          <S>                                                           <C>
          Adjustment to the investment in real estate (see Note B)....  $710,997
          Portion allocated to building and improvements..............        85%
                                                                        --------
          Adjustment to the depreciable basis of Cornerstone
            Partnership's investment in real estate, net..............  $604,347
                                                                        ========
          Additional depreciation expense based on an estimated useful
            life of 40 years..........................................  $ 15,109
                                                                        ========
</TABLE>

(P)  To reverse Cornerstone Partnership's historical amortization of deferred
     lease commissions due to the write-off of deferred lease commissions as a
     result of the merger (see Note E).

(Q) Management has estimated that there will be a reduction of general and
    administrative expenses as a result of the merger of approximately $18.0
    million. The general and administrative expense savings have not been
    included in the pro forma condensed combined statement of operations. There
    can be no assurance that EOP Partnership will be successful in realizing
    such anticipated cost savings.

(R) To reflect the additional depreciation expense on the adjustment to the
    depreciable basis of Cornerstone Partnership's investment in unconsolidated
    joint ventures.

<TABLE>
          <S>                                                           <C>
          Adjustment to the basis of the investment in unconsolidated
            joint ventures............................................   $8,275
          Portion allocated to building and improvements..............       85%
                                                                         ------
          Adjustment to the depreciable basis of Cornerstone
            Partnership's investment in unconsolidated joint
            ventures..................................................   $7,034
                                                                         ======
          Decrease in income from investment in unconsolidated joint
            ventures due to additional depreciation expense pertaining
            to the adjustment to the basis of the investment in joint
            ventures based on an estimated useful life of 40 years....   $  176
                                                                         ======
</TABLE>

(S)  To adjust Cornerstone Partnership's preferred distributions assuming
     Cornerstone Partnership's preferred units were converted into cash on
     January 1, 1999.

(T)  The following table sets forth the computation of basic and diluted
     earnings per unit:

<TABLE>
<CAPTION>
                                                                  HISTORICAL     PRO FORMA
                                                                  -----------   -----------
    <S>                                                           <C>           <C>
    NUMERATOR
    Net income from continuing operations before extraordinary
      items, cumulative effect of a change in accounting
      principle and net gain on sales of real estate available
      for units.................................................     $381,151      $431,910
    Net gain on sales of real estate............................       59,661       190,695
                                                                     --------      --------
    Numerator for basic earnings per unit -- net income from
      continuing operations before extraordinary items and
      cumulative effect of a change in accounting principle
      available for units.......................................     $440,812      $622,605
    Interest expense on convertible promissory note.............           --           746
                                                                     --------      --------
    Numerator for basic and diluted earnings per unit -- net
      income from continuing operations before extraordinary
      items and cumulative effect of a change in accounting
      principle available for units.............................     $440,812      $623,351
                                                                     ========      ========

    DENOMINATOR
    Denominator for basic earnings per unit -- weighted average
      units.....................................................  288,326,547   351,114,475
                                                                  ===========   ===========
    Denominator for diluted earnings per unit -- weighted
      average units.............................................  291,157,204   354,965,413
                                                                  ===========   ===========
</TABLE>

                                       F-8
<PAGE>   186
                       EOP OPERATING LIMITED PARTNERSHIP
   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

<TABLE>
<CAPTION>
                                                                  HISTORICAL     PRO FORMA
                                                                  -----------   -----------
    <S>                                                           <C>           <C>
    BASIC
    Net income from continuing operations before extraordinary
      items, cumulative effect of a change in accounting
      principle and net gain on sales of real estate available
      for units.................................................       $ 1.32        $ 1.23
    Net gain on sales of real estate............................         0.21          0.54
                                                                       ------        ------
    Net income from continuing operations before extraordinary
      items and cumulative effect of a change in accounting
      principle available for units.............................       $ 1.53        $ 1.77
                                                                       ======        ======

    DILUTED
    Net income from continuing operations before extraordinary
      items, cumulative effect of a change in accounting
      principle and net gain on sales of real estate available
      for units.................................................       $ 1.31        $ 1.22
    Net gain on sales of real estate............................         0.20          0.54
                                                                       ------        ------
    Net income from continuing operations before extraordinary
      items and cumulative effect of a change in accounting
      principle available for units.............................       $ 1.51        $ 1.76
                                                                       ======        ======
</TABLE>

                                       F-9
<PAGE>   187

                         EQUITY OFFICE PROPERTIES TRUST

               PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS
                 AS OF AND FOR THE YEAR ENDED DECEMBER 31, 1999
                                  (UNAUDITED)

     The accompanying Unaudited Pro Forma Condensed Combined Balance Sheet as of
December 31, 1999 reflects the following transactions as if they had occurred on
December 31, 1999:

     - the proposed merger of Equity Office Properties Trust and Cornerstone
       Properties Inc.; and

     - the issuance of $500 million of unsecured notes on March 21, 2000, due
       March 2006, coupon rate of 8.4% per annum and effective rate of 8.5% per
       annum.

     The accompanying Unaudited Pro Forma Condensed Combined Statement of
Operations for the year ended December 31, 1999 reflects the following
transactions as if they had occurred on January 1, 1999:

     - the proposed merger of Equity Office Properties Trust and Cornerstone
       Properties Inc.; and

     - the issuance of $500 million of unsecured notes on March 21, 2000, due
       March 2006, coupon rate of 8.4% per annum and effective rate of 8.5% per
       annum.

     In the opinion of management, all significant adjustments necessary to
reflect the effects of the merger have been made.

                                      F-10
<PAGE>   188

                         EQUITY OFFICE PROPERTIES TRUST

                   PRO FORMA CONDENSED COMBINED BALANCE SHEET
                         DECEMBER 31, 1999 (UNAUDITED)
                             (DOLLARS IN THOUSANDS)

<TABLE>
<CAPTION>
                                      EQUITY OFFICE       CORNERSTONE       MERGER AND          EQUITY OFFICE
                                     PROPERTIES TRUST   PROPERTIES INC.        OTHER           PROPERTIES TRUST
                                        HISTORICAL        HISTORICAL      ADJUSTMENTS (A)         PRO FORMA
                                     ----------------   ---------------   ---------------      ----------------
<S>                                  <C>                <C>               <C>                  <C>
ASSETS:
Investment in real estate, net.....    $12,572,153        $3,565,637        $  710,997(B)        $16,848,787
Cash and cash equivalents..........          2,338            19,679                --(C)             22,017
Rent and other receivables.........        193,194            91,968           (77,243)(D)           207,919
Escrow deposits and restricted
  cash.............................         19,754           222,043                --               241,797
Investment in unconsolidated joint
  ventures.........................        865,863            31,725             8,275(B)            905,863
Prepaid expenses and other
  assets...........................        392,756           239,176          (199,275)(E)           432,657
                                       -----------        ----------        ----------           -----------
TOTAL ASSETS.......................    $14,046,058        $4,170,228        $  442,754           $18,659,040
                                       ===========        ==========        ==========           ===========
LIABILITIES AND SHAREHOLDERS'
  EQUITY:
Mortgage debt......................    $ 1,743,871        $1,448,331        $  (40,252)(F)       $ 3,151,950
Unsecured notes....................      3,655,047                --           499,320(G)          4,154,367
Lines of credit....................        453,000           329,000           691,027(H)          1,473,027
Dividend/distribution payable......          5,446                --                --                 5,446
Other liabilities..................        479,167           113,305                --               592,472
                                       -----------        ----------        ----------           -----------
TOTAL LIABILITIES..................      6,336,531         1,890,636         1,150,095             9,377,262
                                       -----------        ----------        ----------           -----------
Commitments and contingencies
Minority Interests:
  EOP Partnership..................        844,427           284,566            46,480(I)          1,175,473
  Partially owned properties.......         39,027            22,532                --                61,559
                                       -----------        ----------        ----------           -----------
TOTAL MINORITY INTERESTS...........        883,454           307,098            46,480             1,237,032
                                       -----------        ----------        ----------           -----------
Shareholders' Equity:
  Preferred shares.................        615,000            50,000           (50,000)(J)           615,000
  Common shares....................          2,516                --               494(K)              3,010
  Additional paid in capital.......      6,208,557         1,922,494          (704,315)(L)         7,426,736
                                       -----------        ----------        ----------           -----------
TOTAL SHAREHOLDERS' EQUITY.........      6,826,073         1,972,494          (753,821)            8,044,746
                                       -----------        ----------        ----------           -----------
TOTAL LIABILITIES AND SHAREHOLDERS'
  EQUITY...........................    $14,046,058        $4,170,228        $  442,754           $18,659,040
                                       ===========        ==========        ==========           ===========
</TABLE>

                                      F-11
<PAGE>   189

                         EQUITY OFFICE PROPERTIES TRUST

              PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS
                FOR THE YEAR ENDED DECEMBER 31, 1999 (UNAUDITED)
                 (DOLLARS IN THOUSANDS, EXCEPT PER SHARE DATA)

<TABLE>
<CAPTION>
                                             EQUITY OFFICE        CORNERSTONE       MERGER        EQUITY OFFICE
                                            PROPERTIES TRUST    PROPERTIES INC.    AND OTHER     PROPERTIES TRUST
                                               HISTORICAL         HISTORICAL      ADJUSTMENTS       PRO FORMA
                                            ----------------    ---------------   -----------    ----------------
                                                                                      (A)
<S>                                         <C>                 <C>               <C>            <C>
REVENUES:
  Rental..................................    $  1,493,196         $455,204        $  6,181(M)     $  1,954,581
  Tenant reimbursements...................         281,358          121,385              --             402,743
  Parking.................................         112,204           27,343              --             139,547
  Other...................................          32,298            5,730              --              38,028
  Fee income..............................           8,939            2,677              --              11,616
  Interest/dividends......................          14,248            4,211              --              18,459
                                              ------------         --------        --------        ------------
    Total revenues........................       1,942,243          616,550           6,181           2,564,974
                                              ------------         --------        --------        ------------
EXPENSES:
  Interest:
    Expense incurred......................         413,995          135,755          90,109(N)          639,859
    Amortization of deferred financing
      costs...............................           4,693            2,004           3,669(O)           10,366
  Depreciation............................         339,751           87,971          15,109(P)          442,831
  Amortization............................          14,545            8,755          (8,755)(Q)          14,545
  Real estate taxes.......................         243,778           71,554              --             315,332
  Insurance...............................           9,589            3,548              --              13,137
  Repairs and maintenance.................         209,630           74,728              --             284,358
  Property operating......................         199,879           52,947              --             252,826
  Ground rent.............................           6,887            1,407              --               8,294
  General and administrative..............          80,927           27,006              --(R)          107,933
                                              ------------         --------        --------        ------------
  Total expenses..........................       1,523,674          465,675         100,132           2,089,481
                                              ------------         --------        --------        ------------
Income before allocation to minority
  interests, income from investment in
  unconsolidated joint ventures and net
  gain on sales of real estate............         418,569          150,875         (93,951)            475,493
Minority Interests:
  EOP Partnership.........................         (48,172)         (34,982)          2,006(S)          (81,148)
  Partially owned properties..............          (1,981)          (5,755)             --              (7,736)
Income from investment in unconsolidated
  joint ventures..........................          13,824              898            (176)(T)          14,546
Net gain on sales of real estate..........          59,661          131,034              --             190,695
                                              ------------         --------        --------        ------------
Net income from continuing operations.....         441,901          242,070         (92,121)            591,850
Put option settlement.....................          (5,658)              --              --              (5,658)
Preferred distributions...................         (43,603)          (3,500)          3,500(U)          (43,603)
                                              ------------         --------        --------        ------------
Net income from continuing operations
  before extraordinary items and
  cumulative effect of a change in
  accounting principle available for
  common shares...........................    $    392,640         $238,570        $(88,621)       $    542,589
                                              ============         ========        ========        ============
Net income from continuing operations
  before extraordinary items and
  cumulative effect of a change in
  accounting principle per weighted
  average common share
  outstanding -- basic....................    $       1.53(V)                                      $       1.78(V)
                                              ============                                         ============
Weighted average common shares
  outstanding -- basic....................     256,045,895                                          305,424,355
                                              ============                                         ============
Net income from continuing operations
  before extraordinary items and
  cumulative effect of a change in
  accounting principle per weighted
  average common share
  outstanding -- diluted..................    $       1.51(V)                                      $       1.76(V)
                                              ============                                         ============
Weighted average common shares
  outstanding -- diluted..................     291,157,204                                          354,965,413
                                              ============                                         ============
</TABLE>

                                      F-12
<PAGE>   190

                         EQUITY OFFICE PROPERTIES TRUST

           NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS
                         DECEMBER 31, 1999 (UNAUDITED)
                 (DOLLARS IN THOUSANDS, EXCEPT PER SHARE DATA)

(A) Represents adjustments to record the merger between Equity Office and
    Cornerstone based upon the assumed purchase price of $4.6 billion assuming a
    market value of $24.6818 per share of Equity Office's common shares and
    adjustments to record the issuance of $500 million in unsecured notes which
    occurred on March 21, 2000. The calculation of the merger acquisition cost
    is as follows:

<TABLE>
          <S>                                                           <C>         <C>
          Issuance of 49.4 million Equity Office common shares and 13.4 million
          EOP Partnership units based on a .7009 exchange rate in exchange for
          70.5 million shares of Cornerstone common stock and 19.1 million
          Cornerstone Partnership units (see Note I).............................   $1,549,719
          Cash portion of merger consideration:
               Cornerstone common stock (58,551,525 @ $18.00).........  1,053,927
               Cornerstone preferred stock (3,030,303 @ $18.00).......     54,545    1,108,472
                                                                        ---------
          Equity Office's current ownership of 250,700 shares of Cornerstone
            common stock.........................................................        3,480
          Assumption of Cornerstone's total liabilities..........................    1,890,636
          Adjustment to Cornerstone's mortgage debt to reflect market value (see
            Note F)..............................................................      (40,252)
          Cornerstone's minority interest allocation for partially owned
            properties...........................................................       22,532
          Merger costs (see calculation below)...................................       78,000
                                                                                    ----------
                    Total merger acquisition cost................................   $4,612,587
                                                                                    ==========
</TABLE>

     The following is a calculation of estimated merger costs:

<TABLE>
          <S>                                                           <C>
          Employee termination costs..................................  $   43,800
          Investment advisory fees....................................      15,000
          Transfer taxes..............................................      10,000
          Legal, accounting and other fees............................       7,700
          Loan assumption fees........................................       1,500
                                                                        ----------
                    Total merger costs................................  $   78,000
                                                                        ==========
</TABLE>

(B)  Represents the estimated increase in Cornerstone's investment in real
     estate based upon the merger acquisition cost to reflect the allocation to
     other tangible assets of Cornerstone being acquired:

<TABLE>
          <S>                                                           <C>
          Meger acquisition cost (see Note A).........................  $4,612,587
                                                                        ----------
          Less basis of Cornerstone's net assets acquired:
               Investment in real estate, net.........................   3,565,637
               Cash and cash equivalents..............................      19,679
               Rent and other receivables (excluding $77.2 million of
                deferred rents receivable)............................      14,725
               Escrow deposits and restricted cash....................     222,043
               Investment in unconsolidated joint ventures............      31,725
               Prepaid expenses and other assets (excluding $199.7
                million of deferred leasing, financing and other costs
                (see Note E)).........................................      39,506
                                                                        ----------
                    Subtotal..........................................   3,893,315
                                                                        ----------
          Adjustment to record fair value of Cornerstone's investment
            in real estate and investment in unconsolidated joint
            ventures, net.............................................     719,272
          Less adjustment allocated to investment in unconsolidated
            joint ventures............................................      (8,275)
                                                                        ----------
          Adjustment allocated to investment in real estate...........  $  710,997
                                                                        ==========
</TABLE>

                                      F-13
<PAGE>   191
                         EQUITY OFFICE PROPERTIES TRUST

   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

(C) There was no change in cash and cash equivalents as a result of the
    following transactions:

<TABLE>
          <S>                                                           <C>
          Anticipated borrowings on additional credit facilities to
            finance the cash portion of the merger (see Note H).......  $   691,027
          Gross proceeds from the $500 million unsecured notes
            offering (see Note G).....................................      500,000
          Less cash portion of merger consideration (see Note A)......   (1,108,472)
          Less merger costs (see Note A)..............................      (78,000)
          Less financing costs related to the $500 million unsecured
            note offering (see Note E)................................       (3,875)
          Less discount on the $500 million unsecured notes offering
            (see Note G)..............................................         (680)
                                                                        -----------
                    Net adjustment to cash and cash equivalents.......  $        --
                                                                        ===========
</TABLE>

(D) Represents the elimination of Cornerstone's deferred rents receivable of
    $77.2 million which arose from the historical straight-lining of rental
    revenue.

(E) Represents an adjustment for the following:

<TABLE>
          <S>                                                           <C>
          Cornerstone's deferred leasing, financing and other costs
            which were not assigned any value in the allocation of the
            merger acquisition cost...................................  $(199,670)
          Transfer of Equity Office's current ownership of 250,700
            shares of Cornerstone common stock to merger acquisition
            cost (see Note A).........................................     (3,480)
          Additional deferred financing costs associated with the $500
            million unsecured notes offering..........................      3,875
                                                                        ---------
                    Total.............................................  $(199,275)
                                                                        =========
</TABLE>

(F)  To adjust Cornerstone's mortage debt to market value.

(G) To reflect the $500 million unsecured notes offering net of a $.7 million
    discount.

(H) To reflect borrowings on additional credit facilities to finance the cash
    portion of the merger as follows:

<TABLE>
          <S>                                                           <C>
          Cash portion of merger consideration (See Note A)...........  $1,108,472
          Merger costs (See Note A)...................................      78,000
          Less net proceeds from the $500 million unsecured notes
            offering (see Note C).....................................    (495,445)
                                                                        ----------
                    Borrowings on additional credit facilities........  $  691,027
                                                                        ==========
</TABLE>

                                      F-14
<PAGE>   192
                         EQUITY OFFICE PROPERTIES TRUST

   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

(I)  To adjust minority interests in the EOP Partnership to reflect the merger
     as follows:

<TABLE>
          <S>                                                           <C>
          Equity Office historical common shareholders' equity and
            minority interests in EOP Partnership.....................  $7,055,500
          Cornerstone historical common shareholders' equity and
            minority interests in Cornerstone Partnership.............   2,207,060
          Pro forma adjustments to common shareholders' equity........    (657,341)
                                                                        ----------
                    Total.............................................   8,605,219
          Minority interests ownership percentage of EOP Partnership
            after the merger (see below)..............................       13.66%
                                                                        ----------
          Minority interest ownership of EOP Partnership after the
            merger....................................................   1,175,473
          Less historical minority interest ownership of EOP
            Partnership prior to the merger...........................    (844,427)
          Less historical minority interest ownership of Cornerstone
            Partnership prior to the merger...........................    (284,566)
                                                                        ----------
                    Adjustment to minority interest ownership of EOP
                      Partnership to reflect the merger...............  $   46,480
                                                                        ==========
</TABLE>

     The 13.66% minority interests ownership of EOP Partnership is calculated as
     follows:

<TABLE>
<CAPTION>
                                                          SHARES        UNITS      SHARES AND UNITS
                                                        -----------   ----------   ----------------
          <S>                                           <C>           <C>          <C>
          Shares of Cornerstone common stock and
            Cornerstone Partnership units outstanding
            at December 31, 1999......................  129,252,303   19,131,785     148,384,088
          Less shares of Cornerstone common stock
            redeemed for cash (see Note A)............  (58,551,525)          --     (58,551,525)
          Less shares of Cornerstone common stock
            currently held by Equity Office (see Note
            A)........................................     (250,700)          --        (250,700)
                                                        -----------   ----------     -----------
          Shares of Cornerstone common stock and
            Cornerstone Partnership units to be
            converted in the merger into Equity Office
            common shares and EOP Partnership units at
            an exchange rate of .7009.................   70,450,078   19,131,785      89,581,863
                                                        ===========   ==========     ===========
          Equity Office common shares and EOP
            Partnership units to be issued in the
            merger....................................   49,378,460   13,409,468      62,787,928
          Equity Office common shares and EOP
            Partnership units outstanding at December
            31, 1999..................................  251,582,434   34,203,912     285,786,346
                                                        -----------   ----------     -----------
          Equity Office common shares and EOP
            Partnership units outstanding after the
            merger....................................  300,960,894   47,613,380     348,574,274
                                                        ===========   ==========     ===========
          Minority interests ownership percentage of
            EOP Partnership...........................        13.66%
                                                        ===========
          Equity Office ownership percentage of EOP
            Partnership...............................        86.34%
                                                        ===========
</TABLE>

(J)  To record the redemption of Cornerstone's preferred stock into cash (see
     Note A).

                                      F-15
<PAGE>   193
                         EQUITY OFFICE PROPERTIES TRUST

   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

(K) To record the par value of 49.4 million Equity Office common shares issued
    to Cornerstone common stockholders.

(L)  To reflect the net decrease in additional paid in capital associated with
     the merger as follows:

<TABLE>
          <S>                                                           <C>
          Issuance of 49.4 million Equity Office common shares and
            13.4 million EOP Partnership units at the .7009 exchange
            rate, in exchange for 70.5 million shares of Cornerstone
            common stock and 19.1 million Cornerstone Partnership
            units (see Note I)........................................  $ 1,549,719
          Less par value of Equity Office common shares issued to
            Cornerstone common stockholders (see Note K)..............         (494)
          Adjustment to minority interests in EOP Partnership (see
            Note I)...................................................      (46,480)
          Less historical minority interests in the ownership of
            Cornerstone Partnership...................................     (284,566)
          Less Cornerstone's historical additional paid in capital....   (1,922,494)
                                                                        -----------
                    Net decrease in paid in capital...................  $  (704,315)
                                                                        ===========
</TABLE>

(M) To reflect the adjustment for the straight-line effect of scheduled rent
    increases.

(N) To reflect the additional interest expense incurred from the $500 million
    unsecured notes offering and borrowings from additional credit facilities to
    finance the cash portion of the merger.

<TABLE>
          <S>                                                           <C>
          Additional borrowings from $500 million unsecured notes
            offering (see Note G) and credit facilities (see Note
            H)........................................................  $1,190,347
          Weighted average interest rate..............................        7.57%
                                                                        ----------
          Additional interest expense.................................  $   90,109
                                                                        ==========
</TABLE>

<TABLE>
<S>  <C>                                                             <C>
(O)  To reflect the amortization of $3.9 million of financing
       costs incurred with the $500 million unsecured notes
       offering over the six-year term...........................     $  646
     To reflect additional amortization of the adjustment to
       Cornerstone's mortgage debt to market value...............      3,023
                                                                      ------
                                                                      $3,669
                                                                      ======
</TABLE>

(P)  To reflect additional depreciation expense related to the adjustment to the
     investment in real estate

<TABLE>
          <S>                                                           <C>
          Adjustment to investment in real estate (see Note B)........  $710,997
          Portion allocated to building and improvements..............        85%
                                                                        --------
          Adjustment to the depreciable basis of Cornerstone's
            investment in real estate, net............................  $604,347
                                                                        ========
          Additional depreciation expense based on an estimated useful
            life of 40 years..........................................  $ 15,109
                                                                        ========
</TABLE>

(Q) To reverse Cornerstone's historical amortization of deferred lease
    commissions due to the write-off of deferred lease commissions as a result
    of the merger (see Note E).

(R) Management has estimated that there will be a reduction of general and
    administrative expenses as a result of the merger of approximately $18.0
    million. The general and administrative expense savings have not been
    included in the pro forma condensed combined statement of operations. There
    can be no assurance that Equity Office will be successful in realizing such
    anticipated cost savings.

(S)  To adjust the minority interests income allocation to EOP Partnership after
     the merger to 13.01%.

                                      F-16
<PAGE>   194
                         EQUITY OFFICE PROPERTIES TRUST

   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

(T)  To reflect the additional depreciation expense on the adjustment to the
     depreciable basis of Cornerstone's investment in unconsolidated joint
     ventures.

<TABLE>
          <S>                                                           <C>
          Adjustment to the basis of the investment in unconsolidated
            joint ventures............................................   $8,275
          Portion allocated to building and improvements..............       85%
                                                                         ------
          Adjustment to the depreciable basis of Cornerstone's
            investment in unconsolidated joint ventures...............   $7,034
                                                                         ======
          Decrease in income from investment in unconsolidated joint
            ventures due to additional depreciation expense pertaining
            to the adjustment to the basis of the investment in joint
            ventures based on an estimated useful life of 40 years....   $  176
                                                                         ======
</TABLE>

(U) To adjust Cornerstone's preferred distributions assuming the shares of
    Cornerstone preferred stock were redeemed for cash on January 1, 1999.

(V) The following table sets forth the computation of basic and diluted earnings
    per common share:

<TABLE>
<CAPTION>
                                                               HISTORICAL     PRO FORMA
                                                               -----------   -----------
                          NUMERATOR
 ------------------------------------------------------------
 <S>                                                           <C>           <C>
 Net income from continuing operations before extraordinary
   items, cumulative effect of a change in accounting
   principle and net gain on sales of real estate available
   for common shares.........................................     $332,979      $351,894
 Net gain on sales of real estate............................       59,661       190,695
                                                                    ------        ------
 Numerator for basic earnings per share -- net income from
   continuing operations before extraordinary items and
   cumulative effect of a change in accounting principle
   available for common shares...............................      392,640       542,589
 Minority interest in EOP Partnership........................       48,172        81,148
 Interest expense on convertible promissory note.............           --           746
                                                                    ------        ------
 Numerator for diluted earnings per share -- net income from
   continuing operations before extraordinary items and
   cumulative effect of a change in accounting principle
   available for common shares...............................     $440,812      $624,483
                                                                    ======        ======

<CAPTION>
                         DENOMINATOR
                         -----------
 <S>                                                           <C>           <C>
 Denominator for basic earnings per share -- weighted average
   common shares.............................................  256,045,895   305,424,355
                                                                    ======        ======
 Denominator for diluted earnings per share -- weighted
   average common shares.....................................  291,157,204   354,965,413
                                                                    ======        ======

<CAPTION>
                            BASIC
                            -----
 <S>                                                           <C>           <C>
 Net income from continuing operations before extraordinary
   items, cumulative effect of a change in accounting
   principle and net gain on sales of real estate available
   for common shares.........................................       $ 1.30        $ 1.15
 Net gain on sales of real estate............................         0.23          0.63
                                                                    ------        ------
 Net income from continuing operations before extraordinary
   items and cumulative effect of a change in accounting
   principle available for common shares.....................       $ 1.53        $ 1.78
                                                                    ======        ======
</TABLE>

                                      F-17
<PAGE>   195
                         EQUITY OFFICE PROPERTIES TRUST

   NOTES TO PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS -- (CONTINUED)

<TABLE>
<CAPTION>
                                                               HISTORICAL     PRO FORMA
                                                               -----------   -----------
 <S>                                                           <C>           <C>
                           DILUTED
                           -------
 Net income from continuing operations before extraordinary
   items, cumulative effect of a change in accounting
   principle and net gain on sales of real estate available
   for common shares.........................................       $ 1.31        $ 1.22
 Net gain on sales of real estate............................         0.20          0.54
                                                                    ------        ------
 Net income from continuing operations before extraordinary
   items and cumulative effect of a change in accounting
   principle available for common shares.....................       $ 1.51        $ 1.76
                                                                    ======        ======
</TABLE>

                                      F-18
<PAGE>   196

                       REPORT OF INDEPENDENT ACCOUNTANTS

To the Partners of Cornerstone
Properties Limited Partnership

In our opinion, the accompanying consolidated balance sheet and the statements
of income, comprehensive income, partners' capital and cash flows present
fairly, in all material respects, the financial position of Cornerstone
Properties Limited Partnership and subsidiaries ("Cornerstone Partnership") at
December 31, 1999, and the results of their operations and their cash flows for
the year then ended, in conformity with accounting principles generally accepted
in the United States. In addition, in our opinion, the financial statement
schedule listed in the accompanying index presents fairly, in all material
respects, the information set forth therein when read in conjunction with the
related consolidated financial statements. These financial statements and
financial statement schedule are the responsibility of the Partnership's
management; our responsibility is to express an opinion on these financial
statements and financial statement schedule based on our audit. We conducted our
audit of these statements in accordance with auditing standards generally
accepted in the United States, which require that we plan and perform the audit
to obtain reasonable assurance about whether the financial statements are free
of material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements, assessing
the accounting principles used and significant estimates made by management, and
evaluating the overall financial statement presentation. We believe that our
audit provides a reasonable basis for the opinion expressed above.

As discussed in Note 1 of the consolidated financial statements, on February 11,
2000, Cornerstone Partnership announced a definitive plan of merger with Equity
Office Properties Operating Limited Partnership.

/s/ PRICEWATERHOUSECOOPERS LLP
PricewaterhouseCoopers LLP

New York, New York
April 12, 2000

                                      F-19
<PAGE>   197

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                          CONSOLIDATED BALANCE SHEETS
                     DECEMBER 31, 1999 AND 1998 (UNAUDITED)
                         (DOLLAR AMOUNTS IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                 1999         1998
                                                              ----------   -----------
                                                                           (UNAUDITED)
<S>                                                           <C>          <C>
ASSETS
Developments in progress:
  Land......................................................  $   46,132   $   10,437
  Development costs.........................................      17,000        2,519
Rental Property at cost:
  Land......................................................     646,852      702,840
  Buildings, leasehold interests and improvements...........   3,084,466    3,403,152
  Deferred lease costs......................................     157,015      143,188
                                                              ----------   ----------
                                                               3,951,465    4,262,136
  Less: Accumulated depreciation and amortization...........     290,998      286,664
                                                              ----------   ----------
     Total Development and Rental Property..................   3,660,467    3,975,472
Assets held for sale........................................      62,185       77,568
Cash and cash equivalents...................................      19,679       61,612
Restricted cash.............................................     222,043        9,114
Investment in unconsolidated joint ventures.................      31,725       31,500
Other deferred costs, net of accumulated amortization of
  $7,092 and $999...........................................      42,655       47,807
Deferred tenant receivables.................................      77,243       53,489
Tenant and other receivables, net...........................      14,725       10,257
Other assets................................................      39,506       14,839
                                                              ----------   ----------
TOTAL ASSETS................................................  $4,170,228   $4,281,658
                                                              ==========   ==========
LIABILITIES
Long-term debt, inclusive of $16,149 and $25,031 of
  unamortized premium.......................................  $1,435,405   $1,519,548
Credit facility.............................................     329,000      465,000
Accrued interest............................................      10,896       10,873
Accrued real estate taxes...................................      16,457       16,395
Accounts payable and accrued expenses.......................      45,006       51,454
Distributions payable.......................................          --       38,163
Unearned revenue and other liabilities......................      40,881       23,890
                                                              ----------   ----------
TOTAL LIABILITIES...........................................   1,877,645    2,125,323
                                                              ----------   ----------
MINORITY INTEREST IN JOINT VENTURES.........................      22,532       23,420
                                                              ----------   ----------
Commitments and contingencies
PARTNERS' CAPITAL
Redeemable preferred units; 344,828 units authorized; 0
  issued and outstanding....................................          --           --
7% Cumulative convertible preferred units, $16.50 stated
  value; 65,000,000 units authorized; 3,030,303 issued and
  outstanding...............................................      50,000       50,000
General Partners' Capital...................................      22,125       20,846
Limited Partners Capital....................................   2,190,514    2,063,769
Accumulated other comprehensive income......................       9,424           --
Deferred compensation.......................................      (2,012)      (1,700)
                                                              ----------   ----------
TOTAL PARTNERS' CAPITAL.....................................   2,270,051    2,132,915
                                                              ----------   ----------
TOTAL LIABILITIES AND PARTNERS' CAPITAL.....................  $4,170,228   $4,281,658
                                                              ==========   ==========
</TABLE>

  The accompanying notes are an integral part of these consolidated financial
                                  statements.

                                      F-20
<PAGE>   198

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
           FOR THE YEARS ENDED DECEMBER 31, 1999 AND 1998 (UNAUDITED)
             (DOLLAR AMOUNTS IN THOUSANDS EXCEPT PER UNIT AMOUNTS)

<TABLE>
<CAPTION>
                                                                  1999           1998
                                                              ------------   ------------
                                                                             (UNAUDITED)
<S>                                                           <C>            <C>
REVENUES
  Office and parking rentals................................  $    607,409   $    321,097
  Earnings in joint ventures................................           898         11,615
  Interest and other income.................................         8,009          6,625
                                                              ------------   ------------
     TOTAL REVENUES.........................................       616,316        339,337
                                                              ------------   ------------
EXPENSES
  Building operating expenses...............................       132,630         71,404
  Real estate taxes.........................................        71,554         44,184
  Interest expense..........................................       137,013         63,426
  Depreciation and amortization.............................        96,726         57,031
  General and administrative................................        27,006         12,393
                                                              ------------   ------------
     TOTAL EXPENSES.........................................       464,929        248,438
                                                              ------------   ------------
                                                                   151,387         90,899
                                                              ------------   ------------
OTHER INCOME (EXPENSES)
  Gain (loss) on sale of real estate assets.................       131,034           (173)
                                                              ------------   ------------
     TOTAL OTHER INCOME (EXPENSES)..........................       131,034           (173)
                                                              ------------   ------------
MINORITY INTEREST IN JOINT VENTURES.........................        (5,755)        (4,399)
                                                              ------------   ------------
Income before cumulative effect of a change in accounting
  principle and extraordinary loss..........................       276,666         86,327
Cumulative effect of a change in accounting principle.......          (630)            --
Extraordinary loss..........................................       (10,787)        (4,303)
                                                              ------------   ------------
NET INCOME..................................................  $    265,249   $     82,024
                                                              ============   ============
INCOME APPLICABLE TO PREFERRED UNITS........................  $     (3,500)  $     (3,500)
                                                              ------------   ------------
INCOME AVAILABLE FOR UNITS..................................  $    261,749   $     78,524
                                                              ============   ============
INCOME BEFORE CUMULATIVE EFFECT OF A CHANGE IN ACCOUNTING
  PRINCIPLE AND EXTRAORDINARY LOSS PER UNIT.................  $       1.84   $       0.80
                                                              ============   ============
EXTRAORDINARY LOSS PER UNIT.................................  $      (0.08)  $      (0.04)
                                                              ============   ============
BASIC INCOME PER UNIT.......................................  $       1.76   $       0.76
                                                              ============   ============
BASIC WEIGHTED AVERAGE UNITS OUTSTANDING....................   148,654,779    103,881,682
                                                              ============   ============
DILUTED INCOME PER UNIT.....................................  $       1.75   $       0.75
                                                              ============   ============
DILUTED WEIGHTED AVERAGE UNITS OUTSTANDING..................   151,830,347    104,252,294
                                                              ============   ============
</TABLE>

  The accompanying notes are an integral part of these consolidated financial
                                  statements.

                                      F-21
<PAGE>   199

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
                 FOR THE YEARS ENDED DECEMBER 31, 1999 AND 1998
                         (DOLLAR AMOUNTS IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                1999        1998
                                                              --------   -----------
                                                                         (UNAUDITED)
<S>                                                           <C>        <C>
Net income..................................................  $265,249     $82,024
                                                              ========     =======
OTHER COMPREHENSIVE INCOME:
  Unrealized gain on investments............................     3,911          --
  Unrealized gain on interest rate swaps during the
     period.................................................     5,513          --
                                                              --------     -------
  OTHER COMPREHENSIVE INCOME................................     9,424          --
                                                              --------     -------
COMPREHENSIVE INCOME........................................  $274,673     $82,024
                                                              ========     =======
</TABLE>

  The accompanying notes are an integral part of these consolidated financial
                                  statements.

                                      F-22
<PAGE>   200

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                  CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL
           FOR THE YEARS ENDED DECEMBER 31, 1999 AND 1998 (UNAUDITED)
                         (DOLLAR AMOUNTS IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                              ACCUMULATED
                                   GENERAL     LIMITED      7% CUMULATIVE        OTHER
                                   PARTNERS    PARTNERS      CONVERTIBLE     COMPREHENSIVE     DEFERRED
                                   CAPITAL     CAPITAL     PREFERRED UNITS      INCOME       COMPENSATION     TOTAL
                                   --------   ----------   ---------------   -------------   ------------   ----------
                                                                       (UNAUDITED)
<S>                                <C>        <C>          <C>               <C>             <C>            <C>
BALANCE, JANUARY 1, 1998.........       --    $       --       $    --          $   --         $    --      $       --
  Contributed capital -- REIT....   10,706     1,059,933        50,000              --          (2,188)      1,118,451
  Contributed
    capital -- others............    6,383       631,915            --              --              --         638,298
  Proceeds from issuance of
    units, net of $14,463 in
    issuance costs...............    4,479       443,402            --              --              --         447,881
  Distribution reinvestment, net
    of $410 in issuance costs....       63         6,231            --              --              --           6,294
  Restricted share awards........        6           571            --              --            (577)             --
  Restricted share awards
    vesting......................       --            --            --              --           1,065           1,065
  Net income.....................      820        81,204            --              --              --          82,024
  Preferred unit distributions...      (35)       (3,465)           --              --              --          (3,500)
  Distributions -- REIT..........   (1,509)     (149,419)           --              --              --        (150,928)
  Distributions -- others........      (67)       (6,603)           --              --              --          (6,670)
                                   -------    ----------       -------          ------         -------      ----------
BALANCE, DECEMBER 31, 1998.......  $20,846    $2,063,769       $50,000          $   --         $(1,700)     $2,132,915
  Unit issuance costs............       (4)         (374)           --              --              --            (378)
  Restricted share awards........       18         1,742            --              --          (1,760)             --
  Restricted share awards
    vesting......................       --            --            --              --           1,448           1,448
  Net income.....................    2,652       262,597            --              --              --         265,249
  Unrealized gain on
    investments..................       --            --            --           3,911              --           3,911
  Unrealized gain on swaps.......       --            --            --           5,513              --           5,513
  Distribution reinvestment......       23         2,295            --              --              --           2,318
  Share awards exercised.........       18         1,809            --              --              --           1,827
  Partner redemptions............      (12)       (1,157)           --              --              --          (1,169)
  Contributed capital -- REIT....        7           695            --              --              --             702
  Repurchase of units for
    treasury.....................      (50)       (4,961)           --              --              --          (5,011)
  Preferred unit distributions...      (35)       (3,465)           --              --              --          (3,500)
  Distributions -- REIT..........   (1,160)     (114,843)           --              --              --        (116,003)
  Distributions -- Others........     (178)      (17,593)           --              --              --         (17,771)
                                   -------    ----------       -------          ------         -------      ----------
BALANCE, DECEMBER 31, 1999.......  $22,125    $2,190,514       $50,000          $9,424         $(2,012)     $2,270,051
                                   =======    ==========       =======          ======         =======      ==========
</TABLE>

  The accompanying notes are an integral part of these consolidated financial
                                  statements.

                                      F-23
<PAGE>   201

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                     CONSOLIDATED STATEMENTS OF CASH FLOWS
           FOR THE YEARS ENDED DECEMBER 31, 1999 AND 1998 (UNAUDITED)
                         (DOLLAR AMOUNTS IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                1999        1998
                                                              --------   -----------
                                                                         (UNAUDITED)
<S>                                                           <C>        <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
  Net income................................................  $265,249    $  82,024
  Adjustments to reconcile net income to net cash provided
    by operating activities:
    Depreciation and amortization...........................    90,790       56,733
    Deferred compensation amortization......................     1,312        1,016
    Net change in real estate joint ventures................      (225)       5,670
    Cumulative effect of a change in accounting principle...       630           --
    Net gain on interest rate swap..........................        --           --
    Extraordinary loss......................................    10,787        4,303
    Unbilled rental revenue.................................   (25,858)     (13,712)
    Increase in accrued interest............................        23        6,739
    Minority interest share of income.......................     5,755        4,399
    Loss on sale of real estate assets......................  (131,034)        (173)
    Increase in tenant and other receivables and other
     assets.................................................   (15,745)      (6,902)
    Increase in accounts payable, accrued expenses and other
     liabilities............................................    21,431       33,515
                                                              --------    ---------
      Total adjustments.....................................   (42,134)      91,588
                                                              --------    ---------
      Net cash provided by operating activities.............   223,115      173,612
                                                              --------    ---------
CASH FLOWS FROM INVESTING ACTIVITIES:
  Additions to investment property..........................   (79,359)    (797,181)
  Repayment of notes receivable.............................       134        1,518
  Other investments.........................................    (5,000)     (41,893)
  Investments in real estate joint ventures.................        --      (31,391)
  Proceeds from sale of real estate assets net of amounts in
    escrow..................................................   136,713       19,117
                                                              --------    ---------
      Net cash provided by (used in) investing activities...    52,488     (849,830)
                                                              --------    ---------
CASH FLOWS FROM FINANCING ACTIVITIES:
  Proceeds from Units issued................................        --      462,344
  Contributed capital -- REIT...............................       647       60,406
  Repurchase of units for treasury shares...................    (4,889)          --
  Borrowings under mortgage loans...........................   455,000       92,377
  Borrowings under credit facility..........................   130,000      567,500
  Repayments under credit facility..........................  (266,000)    (289,500)
  Repayments under mortgage loans...........................  (432,958)      (3,426)
  Proceeds from distribution reinvestment plan..............     2,318        6,704
  Debt prepayment costs.....................................   (14,898)      (1,762)
  Increase in restricted cash...............................    (2,542)      (7,211)
  Unit issuance costs.......................................    (2,758)     (20,813)
  Option exercise...........................................     1,827           --
  Unitholder redemptions....................................    (1,169)          --
  Distributions to minority interest in joint ventures......    (6,643)      (5,855)
  Distributions to preferred unitholders....................    (3,500)      (3,500)
  Distributions to unitholders..............................  (171,971)    (119,434)
                                                              --------    ---------
      Net cash (used in) provided by financing activities...  (317,536)     737,830
                                                              --------    ---------
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS............   (41,933)      61,612
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR................    61,612           --
                                                              --------    ---------
CASH AND CASH EQUIVALENTS, END OF YEAR......................  $ 19,679    $  61,612
                                                              ========    =========
</TABLE>

  The accompanying notes are an integral part of these consolidated financial
                                  statements.

                                      F-24
<PAGE>   202

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
                           DECEMBER 31, 1999 AND 1998

1.  NATURE OF COMPANY'S BUSINESS AND SIGNIFICANT
    ACCOUNTING POLICIES

NATURE OF THE COMPANY'S BUSINESS

     As used herein, "Company" refers to Cornerstone Properties Limited
Partnership, a Delaware limited partnership, individually or together with its
subsidiaries. The Company is a subsidiary of Cornerstone Properties Inc. (the
"Trust"), a self-administered equity real estate investment trust ("REIT"). The
Company owns, through subsidiaries, interests in 83 Class A office buildings
comprising approximately 17 million rentable square feet, a shopping center, a
hotel and developable land (collectively, the "Properties," and each interest, a
"Property"). The Properties are primarily located in nine major metropolitan
areas throughout the United States: Atlanta, Boston, suburban Chicago,
Minneapolis, New York City, San Francisco Bay Area, Seattle, Southern California
and Washington, D.C. and surrounding suburbs. The Company's strategy is to own
and develop Class A office properties in prime Central Business District
locations and major suburban office markets in U.S. metropolitan areas. Class A
office properties are generally considered to be those that have the most
favorable locations and physical attributes, command premium rents and
experience the highest tenant retention rates within their markets. The Company
also provides property management, leasing, development and tenant improvement
services to third parties on a fee basis through WCP Services, Inc., a taxable
corporate subsidiary in which the Company owns 95% of the equity, but only 1% of
the voting common stock. Substantially all of the Trust's operations are
conducted through the Company. The Trust is the managing general partner of the
Company.

     On February 11, 2000, the Trust announced that it had entered into an
agreement and plan of merger with Equity Office Properties Trust ("EOP") (the
"EOP Merger"). The merger agreement provides for a merger of the Trust with and
into EOP and a merger of the Company with and into EOP Operating Limited
Partnership. In the mergers, holders of common stock of the Trust and holders of
Units in the Company shall be entitled to elect to receive, for each share or
unit, as the case may be, either 0.7009 of a share of beneficial interest of EOP
(or, in the case of the Company Units, 0.7009 of a Class A Unit of EOP Operating
Limited Partnership), or $18.00 per share (or per Unit, as the case may be) in
cash, subject to pro ration as provided in the merger agreement. Each share of
the Trust's 7% Cumulative Convertible Preferred Stock, liquidation preference
$16.50 per share, shall be converted into the right to receive $18.00, plus
accrued and unpaid dividends, in cash. For U.S. federal income tax purposes, the
merger is expected to be tax-free to the Trust's stockholders who are U.S.
persons and who receive EOP shares in the merger, except that any such
stockholder who receives cash in addition to EOP shares generally will recognize
gain (but not loss) in an amount equal to the amount of cash received in the
merger, or, if less, the excess of the fair market value of the EOP shares and
cash received in the merger over the stockholder's basis in the common stock
exchanged in the merger. The merger is also expected in most cases to be
tax-free to stockholders who are non-U.S. persons, although certain non-U.S.
stockholders may be subject to U.S. tax under the provisions of the Foreign
Investment in Real Property Tax Act. The mergers are subject to customary
closing conditions, including the approval of the merger by the shareholders of
EOP and the stockholders of the Trust and the approval of the partnership
merger, to the extent necessary, by the partners of EOP Operating Limited
Partnership and the Company.

PRINCIPLES OF CONSOLIDATION

     The Company has consolidated the following partnerships because it has a
majority interest in the economic benefits and is or has the right to become the
managing general partner at its sole discretion: NWC Limited Partnership
("NWC"); Third and University Limited Partnership ("Third Partnership"); Two
Twenty Two Berkeley Venture ("222 Berkeley"); Five Hundred Boylston West Venture
("500

                                      F-25
<PAGE>   203
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

1.  NATURE OF COMPANY'S BUSINESS AND SIGNIFICANT
    ACCOUNTING POLICIES -- (CONTINUED)
Boylston"); One Ninety One Peachtree Associates ("191 Peachtree"); 191 Finance
Associates, L.P. ("191 Finance"); Avenue Associates Limited Partnership ("Market
Square"); and 120 Montgomery Associates, LLC ("120 Montgomery"). The Company's
investments in the One Post Property and WCP Services, Inc. are accounted for as
equity investments (see Note 4). All significant intercompany balances and
transactions have been eliminated in consolidation.

INVESTMENT PROPERTY

     The costs of the buildings, garages, leasehold interests and improvements
are being depreciated using the straight-line method over their estimated useful
lives, ranging from 20 years for electrical and mechanical installations to 40
years for structural components. Tenant improvements are being amortized over
the terms of the related leases.

     Investment properties are carried at cost less accumulated depreciation.
Whenever events or changes in circumstances indicate that the carrying value of
an asset may not be recoverable (such as a significant adverse action by a
regulator, a significant physical change in the property or significant changes
in market conditions), the Company's policy is to assess any impairment in value
by making a comparison of the current and projected cash flows of each property
over its remaining useful life (undiscounted and without interest charges) to
the carrying amount of each property. Such carrying amount would be adjusted, if
necessary, to estimated fair value to reflect the impairment in value of the
property. No significant adjustments have been made in the accompanying
financial statements.

     Costs directly related to the acquisition and development of rental
properties are capitalized. Capitalized development costs include interest,
property taxes, insurance and other project costs incurred during the period of
construction. Ordinary repairs and maintenance are expensed as incurred; major
replacements and betterments, which improve or extend the life of the asset, are
capitalized and depreciated over their estimated useful lives.

ASSETS HELD FOR SALE

     Included in Assets Held for Sale at December 31, 1999 are four properties,
which are expected to be sold by the Company within the next year. The
Properties are valued at approximately $62.2 million, the lower of the carrying
amount or the fair value less estimated costs to sell. For the year ended
December 31, 1999, the fair value less estimated costs to sell exceeds the
carrying amount for each of these properties and therefore, the Company has not
recorded a write down on these assets. The Company discontinues the recognition
of depreciation on the assets when the property is considered held for sale.

CASH AND CASH EQUIVALENTS

     For purposes of reporting cash flows, cash and cash equivalents include
investments with original maturities of three months or less from the date of
purchase. At December 31, 1999 and 1998, the Company had on deposit with major
financial institutions substantially all of its cash and cash equivalents which
balances at times exceed federally insurable limits. The Company believes it
mitigates its risk by investing in or through major financial institutions.
Recoverability of investments is dependent upon the performance of the issuer.

                                      F-26
<PAGE>   204
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

1.  NATURE OF COMPANY'S BUSINESS AND SIGNIFICANT
    ACCOUNTING POLICIES -- (CONTINUED)
DEFERRED LEASE COSTS

     As an inducement to execute a lease, incentives are sometimes offered which
may include cash and/or other allowances. These incentives and other lease
costs, such as commissions, which are directly related to specific leases, are
deferred and amortized over the terms of the related leases.

OTHER DEFERRED COSTS

     Costs incurred in the underwriting and issuance of long-term debt and
revolving lines of credit are being amortized over the term of the debt. As part
of the acquisition of the DIHC Portfolio (see Note 2), the Trust purchased
several management contracts to which Stichting Pensioenfonds Voor de Gezondheid
Geestelijke en Maatschappelijke Belangen ("PGGM") was a party, which were
subsequently contributed to the Company. The price paid for these contracts is
being amortized over four years. Included in Other Deferred Costs is the
purchase price for the intangible management and development company assets that
were acquired as part of the Wilson Acquisition which are being amortized over a
term of ten years (see Note 2).

OTHER ASSETS

     The Company records costs incurred for potential investments as Other
Assets. Upon consummation of an investment, the Company capitalizes all such
costs as an adjustment to the purchase price and depreciates these costs over
the useful life of the asset. All such costs are expensed at the time it is
determined that a potential investment will not be consummated. In addition, the
Company adopted EITF 97-11 and in accordance therewith, the Company expenses all
internal acquisition costs.

     Included in Other Assets is the Company's $1.5 million equity investment in
Allied Riser Communications Corp. ("ARC") and its $3.5 million equity investment
in Cypress Communications, Inc. ("Cypress"). ARC and Cypress are providers of
voice, video and data telecommunications services. As part of the terms of the
agreements with both ARC and Cypress, the Company received warrants for shares
of common stock by providing ARC and Cypress access to certain of the Company's
buildings. As such, the value of the warrants received from ARC and Cypress of
$5.1 million and $2.1 million, respectively, is included in Other Assets. Per
the applicable requirements of Statement of Financial Accounting Standards No.
115 ("SFAS 115"), the Company recorded an unrealized gain on its total
investment in ARC as of December 31, 1999 of $3.9 million. A corresponding
adjustment was posted to a separate component of partner's capital through Other
Comprehensive Income. As of December 31, 1999, Cypress was not publicly traded
and did not fall within the scope of SFAS 115.

MINORITY INTEREST

     Minority interest in joint ventures represents the minority partner's or
venture's capital account balances in NWC, Third Partnership, 222 Berkeley, 500
Boylston, 191 Peachtree, 191 Finance, Market Square and 120 Montgomery. Debit
balances in certain of these capital accounts originated through special cash
distributions in excess of the partner's share of income in accordance with
certain provisions of the respective partnership and joint venture agreements.
Reliability of the debit balances is continually monitored by calculating pro
forma sales proceeds under the respective agreements.

                                      F-27
<PAGE>   205
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

1.  NATURE OF COMPANY'S BUSINESS AND SIGNIFICANT
    ACCOUNTING POLICIES -- (CONTINUED)
REVENUE RECOGNITION

     Rental revenue is recognized ratably as earned over the terms of the
leases. Deferred tenant receivables result from rental revenues, which have been
earned but will be received in future periods as a result of rent concessions
provided to tenants and scheduled future rent increases. Deferred tenant
receivables were approximately $77,243,000 and $53,489,000 at December 31, 1999
and 1998, respectively. Expense reimbursement and escalation income for the
years ended December 31, 1999 and 1998 was approximately $101,595,000 and
$77,821,000, respectively.

     An allowance for doubtful accounts of approximately $3,803,000 and $253,000
has been recorded at December 31, 1999 and 1998, respectively, relating to
tenant and other receivables. Bad debt expense totaled approximately $3,694,000
and $232,000 during 1999 and 1998 respectively. The Company's policy is to
reserve against all trade receivables greater than 90 days past due.

INTEREST RATE SWAP AGREEMENTS

     The Company uses interest rate swaps to effectively fix the interest rates
on certain floating-rate debt. Specific types of loans and amounts that are
hedged are determined based on prevailing market conditions and the current
shape of the yield curve. The specific terms and notional amount of the swaps
are determined based on management's assessment of future interest rates, as
well as short-term strategic initiatives.

     During 1999, the Company entered into and subsequently amended swap
agreements that effectively fixed the rate on $250.0 million of the amount
outstanding on the Company's Revolving Credit Facility at 6.47% for 1999 and
5.41% through the maturity of the swaps in December 2000. The swaps have been
designated as "cash flow hedges" within the meaning defined in SFAS 133 (as
defined hereinafter). At December 31, 1999, the Company recorded an unrealized
gain of $5,513,000 in Other Assets with a corresponding adjustment posted to a
separate component of partners' capital through Other Comprehensive Income as
defined in Statement of Financial Accounting Standards No. 130. Based on the
expiration of these instruments, the unrealized gain is expected to be
reclassified to earnings during the next twelve months. These swaps are
considered hedges for federal income tax purposes.

FEDERAL INCOME TAXES

     The Company is not liable for federal taxes as the partners recognize their
proportionate share of the Company's income or loss in their tax returns. The
Trust has elected to be taxed as a REIT under Sections 856-859 of the United
States Internal Revenue Code (the "Code"). Under these sections of the Code, the
Trust is permitted to deduct dividends paid to stockholders in computing its
taxable income. All taxable earnings and profits of the Trust since inception
have been distributed to the stockholders.

RECENTLY ISSUED ACCOUNTING STANDARDS

     During the first quarter of 1999, the Company adopted Statement of
Financial Accounting Standards No. 133, "Accounting for Derivative Instruments
and Hedging Activities" ("SFAS 133"). SFAS 133 requires that all derivative
instruments be recorded on the balance sheet at their fair value. Changes in the
fair value of derivatives are recorded each period in current earnings or in
other comprehensive income, depending on whether a derivative is designated as
part of a hedge transaction and, if it is, the type of hedge transaction.

                                      F-28
<PAGE>   206
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

1.  NATURE OF COMPANY'S BUSINESS AND SIGNIFICANT
    ACCOUNTING POLICIES -- (CONTINUED)
     During the first quarter of 1999, the Company also adopted Statement of
Position 98-5, "Reporting on the Costs of Start-Up Activities" ("SOP 98-5"). SOP
98-5 requires that certain costs incurred in conjunction with start-up and
organizational activities be expensed. Pursuant to the requirements of SOP 98-5,
the Company has written off all unamortized organizational costs and has
recorded a cumulative effect of a change in accounting principle of $630,044.

     In addition, during the first quarter of 1999, the Company adopted
Statement of Position 98-1, "Accounting for the Costs of Computer Software
Developed or Obtained for Internal Use" ("SOP 98-1"). SOP 98-1 provides guidance
on whether the costs of computer software developed or obtained for internal use
should be capitalized or expensed. The adoption of SOP 98-1 did not have a
significant effect on the Company's financial statements.

ESTIMATES AND RISKS

     The preparation of financial statements in conformity with generally
accepted accounting principles ("GAAP") requires management to make estimates
and assumptions that affect the reported amounts of assets and liabilities and
disclosure of contingent assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the
reporting period. The most significant risks, estimates and assumptions are
related to the recoverability and depreciable lives of investment property, and
the recoverability of deferred tenant receivables and the qualification of the
Trust as a REIT. Actual results could differ from those estimates.

2.  PROPERTIES

     The following table summarizes the Company's interest in real estate
investments at December 31, 1999:

<TABLE>
<CAPTION>
                MARKET NAME                   TOTAL RENTABLE     COMPANY        YEAR
                  PROPERTY                     SQUARE FEET     INTEREST(A)   CONSTRUCTED   LEASED   NOTES
                -----------                   --------------   -----------   -----------   ------   -----
<S>                                           <C>              <C>           <C>           <C>      <C>
BOSTON, MASSACHUSETTS
  Sixty State Street........................       823,014        100.0%        1979        100%       B
  500 Boylston Street.......................       714,513         91.5%        1988        100%       C
  222 Berkeley Street.......................       530,844         91.5%        1991        100%       C
  125 Summer Street.........................       463,691        100.0%        1989         74%
  One Memorial Drive........................       352,764        100.0%        1985        100%       D
                                                ----------                                  ---
  MARKET TOTAL..............................     2,884,826                                   96%
SAN MATEO COUNTY, CALIFORNIA
  Bayhill (4 buildings).....................       514,255        100.0%     1982-1987       96%       E
  Peninsula Office Park (7 buildings).......       492,044        100.0%     1971-1998      100%       E
  Seaport Centre............................       463,418        100.0%        1988        100%       E
  Bay Park Plaza (2 buildings)..............       257,058        100.0%     1985-1998      100%       E
  One Bay Plaza.............................       176,533        100.0%        1979         99%       E
                                                ----------                                  ---
  MARKET TOTAL..............................     1,903,308                                   99%
</TABLE>

                                      F-29
<PAGE>   207
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

2.  PROPERTIES -- (CONTINUED)

<TABLE>
<CAPTION>
                MARKET NAME                   TOTAL RENTABLE     COMPANY        YEAR
                  PROPERTY                     SQUARE FEET     INTEREST(A)   CONSTRUCTED   LEASED   NOTES
                -----------                   --------------   -----------   -----------   ------   -----
<S>                                           <C>              <C>           <C>           <C>      <C>
ATLANTA, GEORGIA
  191 Peachtree Street......................     1,215,288         80.0%        1991         98%     C,F
  200 Galleria..............................       432,698        100.0%        1985         98%       C
                                                ----------                                  ---
  MARKET TOTAL..............................     1,647,986                                   98%
EAST BAY, CALIFORNIA
  Corporate Centre (2 buildings)............       329,348        100.0%     1985-1987       96%       E
  ADP Plaza (2 buildings)...................       300,308        100.0%     1987-1989       95%       E
  PeopleSoft Plaza..........................       277,562        100.0%        1984        100%       E
  Norris Tech Center (3 buildings)..........       260,513        100.0%     1984-1990      100%       E
  Golden Bear Center........................       160,587        100.0%        1986         99%       E
  2700 Ygnacio Valley Road..................       103,214        100.0%        1984         99%       E
  Park Plaza................................        87,040        100.0%        1986        100%       E
  1600 South Main...........................        83,277        100.0%        1983         98%       E
                                                ----------                                  ---
  MARKET TOTAL..............................     1,601,849                                   98%
SEATTLE, WASHINGTON
  Washington Mutual Tower (3 buildings).....     1,154,560         50.0%        1988         98%       G
  110 Atrium Place..........................       215,172        100.0%        1981        100%       E
  Island Corporate Center...................       100,009        100.0%        1987         97%       E
                                                ----------                                  ---
  MARKET TOTAL..............................     1,469,741                                   98%
SANTA CLARA COUNTY, CALIFORNIA
  Pruneyard Office (3 buildings)............       354,629        100.0%     1971-1999       99%     E,H
  10 Almaden................................       294,809        100.0%        1989        100%       E
  Pruneyard Shopping Center.................       252,210        100.0%       1970s         90%       E
  Embarcadero Place (4 buildings)...........       192,081        100.0%        1984        100%       E
  Pruneyard Inn.............................        94,500        100.0%        1989        N/A      E,I
                                                ----------                                  ---
  MARKET TOTAL..............................     1,188,229                                   98%
SAN FRANCISCO, CALIFORNIA
  120 Montgomery Street.....................       420,310         66.7%        1955         95%       E
  One Post..................................       391,450         50.0%        1969         99%       E
  201 California Street.....................       240,230        100.0%        1980         96%       J
  188 Embarcadero...........................        85,183        100.0%        1985         99%       E
                                                ----------                                  ---
  MARKET TOTAL..............................     1,137,173                                   97%
MINNEAPOLIS, MINNESOTA
  Norwest Center............................     1,117,439         50.0%        1988        100%       K
                                                ----------                                  ---
  MARKET TOTAL..............................     1,117,439                                  100%
WASHINGTON, D.C./ALEXANDRIA, VIRGINIA
  Market Square (2 buildings)...............       688,709         70.0%        1990         99%     C,L
  99 Canal Center...........................       137,945        100.0%        1986        100%       C
  TransPotomac Plaza 5......................        96,392        100.0%        1983        100%       C
  11 Canal Center...........................        70,365        100.0%        1986         98%       C
                                                ----------                                  ---
  MARKET TOTAL..............................       993,411                                   99%
</TABLE>

                                      F-30
<PAGE>   208
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

2.  PROPERTIES -- (CONTINUED)

<TABLE>
<CAPTION>
                MARKET NAME                   TOTAL RENTABLE     COMPANY        YEAR
                  PROPERTY                     SQUARE FEET     INTEREST(A)   CONSTRUCTED   LEASED   NOTES
                -----------                   --------------   -----------   -----------   ------   -----
<S>                                           <C>              <C>           <C>           <C>      <C>
SUBURBAN CHICAGO, ILLINOIS
  Corporate 500 Centre (4 buildings)........       679,039        100.0%     1986/1990       99%       M
  One Lincoln Centre........................       297,040        100.0%        1986         89%
                                                ----------                                  ---
  MARKET TOTAL..............................       976,079                                   96%
SANTA MONICA/WEST LOS ANGELES, CALIFORNIA
  West Wilshire (2 buildings)...............       235,787        100.0%     1960-1976       94%       E
  Wilshire Palisades........................       186,714        100.0%        1981        100%       J
  Janss Court...............................       125,709        100.0%        1989        100%     E,N
  Searise Office Tower......................       122,292        100.0%        1975        100%       E
  Commerce Park.............................        94,367        100.0%        1977         79%     E,O
  429 Santa Monica..........................        83,243        100.0%        1982         88%       E
                                                ----------                                  ---
  MARKET TOTAL..............................       848,112                                   95%
ORANGE COUNTY, CALIFORNIA
  Bixby Ranch...............................       277,289        100.0%        1987         98%       E
  18301 Von Karman..........................       219,508        100.0%        1991         88%       E
  2677 North Main...........................       213,318        100.0%        1987         94%       E
                                                ----------                                  ---
  MARKET TOTAL..............................       710,115                                   94%
SAN DIEGO, CALIFORNIA
  Centerside II.............................       286,949        100.0%        1987         93%       E
  Crossroads................................       133,553        100.0%        1983        100%       E
                                                ----------                                  ---
  MARKET TOTAL..............................       420,502                                   95%
NEW YORK CITY, NEW YORK
  527 Madison Avenue........................       215,332        100.0%        1986        100%
  Tower 56..................................       163,633        100.0%        1983         99%       P
                                                ----------                                  ---
  MARKET TOTAL..............................       378,965                                   99%
LOS ANGELES, CALIFORNIA
  700 North Brand...........................       202,531        100.0%        1981         94%       E
  Warner Park Center........................        57,366        100.0%        1986        100%       E
                                                ----------                                  ---
  MARKET TOTAL..............................       259,897                                   95%
CONEJO VALLEY (VENTURA), CALIFORNIA
  Westlake Spectrum (2 buildings)...........       118,990        100.0%        1990         97%       E
  Agoura Hills..............................       115,208        100.0%        1987        100%       E
                                                ----------                                  ---
  MARKET TOTAL..............................       234,198                                   99%
</TABLE>

                                      F-31
<PAGE>   209
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

2.  PROPERTIES -- (CONTINUED)

<TABLE>
<CAPTION>
                MARKET NAME                   TOTAL RENTABLE     COMPANY        YEAR
                  PROPERTY                     SQUARE FEET     INTEREST(A)   CONSTRUCTED   LEASED   NOTES
                -----------                   --------------   -----------   -----------   ------   -----
<S>                                           <C>              <C>           <C>           <C>      <C>
OTHER REGIONS
  U.S. West (Murray, Utah)..................       136,608        100.0%        1985         76%       E
  Exposition Centre (Sacramento,
     California)............................        72,971        100.0%        1984         70%       E
                                                ----------                                  ---
  MARKET TOTAL..............................       209,579                                   74%
  TOTAL PORTFOLIO...........................    17,981,409                                   97%
  Minority Interest Adjustment(Q)...........      (728,307)
                                                ----------
  CORNERSTONE PORTFOLIO.....................    17,253,102                                   96%
  Adjustment For Pruneyard Inn..............       (94,500)
                                                ----------
  CORNERSTONE OFFICE PORTFOLIO..............    17,158,602
                                                ==========
</TABLE>

- ---------------
 (A) Unless noted below, cash flow and residual proceeds will be distributed to
     the Company according to its percentage interest.

 (B) On December 31, 1997, the Trust purchased the second mortgage on Sixty
     State Street. The mortgage is a cash flow mortgage through which all the
     economic benefits/risks (subject to the first mortgage) inure to the
     Company. The Company controls all major decisions regarding management and
     leasing. The total purchase price for the second mortgage was $131.5
     million and is consolidated in buildings due to the above factors. The
     $78.4 million first mortgage on the Property was originally recorded by the
     Trust as an $89.6 million liability due to its above-market interest rate.
     As of January 20, 1998 all of the interest stated above were contributed to
     the Company in exchange for units.

     The second mortgage, which the Company holds, is collateralized only by the
     improvements on Sixty State Street. Title to the improvements is owned by
     Sixty State Street Trust, the ground lessee under a ground lease that
     expires on December 28, 2067. The lease payments on the ground lease are
     $398,896 per annum throughout the term.

 (C) On October 27, 1997, the Trust acquired interests in nine Class A office
     properties comprising approximately 4.5 million rentable square feet in
     Alexandria, Virginia (3 properties), Atlanta (2 properties), Boston (2
     properties), Charlotte and Washington, D.C., as well as an undeveloped
     parcel of land in Chicago (collectively, "the DIHC Portfolio"). The Trust
     acquired the DIHC Portfolio for a purchase price of approximately $1.06
     billion, consisting of approximately 34.2 million shares of Common Stock
     valued and recorded at $16.00 per share, approximately $260.0 million in
     cash and $250.0 million in promissory notes. The cash portion of the
     acquisition was financed with proceeds from the Trust's initial public
     offering in April 1997 and $54.0 million from its Revolving Credit
     Facility. As of January 20, 1998 all of the interest stated above were
     contributed to the Company in exchange for units. The Company has since
     sold the asset in Charlotte as well as the undeveloped parcel of land in
     Chicago.

 (D) On April 28, 1998, the Company purchased One Memorial Drive in Cambridge,
     Massachusetts. The total purchase price for the Property was approximately
     $112.5 million, approximately $23.5 million of which was paid in cash,
     approximately $29.0 million of which was paid in Units valued at $17.50 per
     unit and approximately $60.0 million of which was paid in the Trust's
     Common Stock valued at $17.50 per share.

 (E) Property was acquired as a result of the Wilson Acquisition in December
     1998. After receiving stockholder approval on December 14, 1998, the
     Company acquired substantially all of the properties and real estate
     operations of William Wilson & Associates and related entities ("WW&A")
     (the

                                      F-32
<PAGE>   210
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

2.  PROPERTIES -- (CONTINUED)
     "Wilson Acquisition"). As part of the Wilson Acquisition, the Company
     acquired interests in 69 Class A office Properties, comprising
     approximately 9.2 million rentable square feet primarily in the San
     Francisco Bay Area and in Southern California, a shopping center consisting
     of approximately 252,000 rentable square feet in Santa Clara, California, a
     hotel consisting of 94,500 square feet in Santa Clara, California and 12.8
     acres of developable land in the San Francisco Bay Area. The Company has
     since sold eleven assets comprising approximately 1.2 million square feet.

      The Company acquired WW&A for a purchase price of approximately $1.8
      billion, consisting of approximately 14.9 million shares of the Trust's
      Common Stock valued at $17.25 per share (recorded at $16.25 per share for
      GAAP purposes), approximately 16.2 million Units valued at $17.25 per unit
      (recorded at $16.25 per unit for GAAP purposes), approximately $465.0
      million in cash and the assumption of approximately $760.0 million of
      property and construction related debt (recorded at $773.7 million for
      GAAP purposes). The cash portion of the transaction was financed primarily
      from the Company's Revolving Credit Facility and the sale of $200.0
      million of Common Stock to PGGM, an approximate 33.6% stockholder prior to
      the Wilson Acquisition, priced at $17.25 per share.

 (F) While the Company's stated interest in the partnership that owns 191
     Peachtree Street is 80.0%, its economic interest is significantly larger
     since it has acquired the first mortgage note on the Property in the amount
     of $145.0 million, which earns interest at 9.375% and will receive a
     priority distribution on its acquired capital base. In 1999, the partner in
     the transaction, CH Associates, Ltd., received an annual Incentive
     Distribution (as defined) of $250,000, with the Company receiving the
     remainder of the cash flow of the Property.

     The partnership that owns 191 Peachtree Street leases a portion of the land
     upon which the project is located pursuant to a ground lease agreement. The
     agreement requires annual payments of $45,000 through January 31, 2002 and
     $75,000 through January 31, 2008. Thereafter, the annual rent increases
     $2,500 per year until the expiration date of January 31, 2087. The
     partnership records ground rental expense relating to this agreement on a
     straight-line basis. The ground lease is renewable for an additional 99
     years.

(G) While the Company's stated interest in the partnership that owns Washington
    Mutual Tower is 50.0%, its economic interest in the Property is
    significantly larger due to priority distributions it receives on its
    invested capital base. For the year ended December 31, 1999, the Company
    received 100% of the cash distributions from the partnership that owns
    Washington Mutual Tower.

(H) Pruneyard Place construction was completed and occupied on April 1, 1999.
    The building was entirely pre-leased.

 (I) The Pruneyard Inn is a three-story hotel. An expansion was completed in May
     1999, increasing the number of rooms from 118 to 172.

 (J) On June 3, 1998, the Company purchased 201 California Street and Wilshire
     Palisades. The total purchase price for the Properties was approximately
     $121.5 million, approximately $29.5 million of which was paid in cash,
     approximately $29.1 million of which was paid in Units valued at $17.50 per
     unit and approximately $62.9 million of assumed debt (recorded at $64.6
     million for GAAP purposes).

 (K) While the Company's stated interest in the partnership that owns Norwest
     Center is 50.0%, its economic interest in the Property is significantly
     larger due to priority distributions it receives on its invested capital
     base. For the year ended December 31, 1999, the Company's share of earnings
     and cash distributions from the partnership that owns Norwest Center was
     74.4%.

                                      F-33
<PAGE>   211
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

2.  PROPERTIES -- (CONTINUED)

 (L) During 1998, through a series of transactions, the Company acquired
     partnership interests with a stated interest of approximately 70.0% in the
     partnerships that own Market Square. The Company's economic interest is
     significantly larger since it has acquired the first mortgage note on the
     Property in the amount of $181.0 million which earns interest at 9.75% and
     will receive a priority distribution on its acquired capital base. In
     addition, the Company acquired a "buffer loan", with accrued principal and
     interest of $49.0 million at purchase, which accrues interest at a rate of
     Prime plus 1.25% and is payable from cash flow, refinancing or sales
     proceeds in excess of the first mortgage. During the year ended December
     31, 1999, the Company received 100% of the cash flow from the Property. On
     November 14, 1998, the Company purchased an additional interest in the
     partnerships that own Market Square which enabled it to gain sufficient
     control in order to consolidate the investment.

(M) On January 28, 1998, the Company purchased Corporate 500 Centre in
    Deerfield, Illinois. This Property consists of four Class A office buildings
    with approximately 679,000 rentable square feet. The consideration paid for
    this Property was approximately $135.0 million in cash and approximately
    $15.0 million in Units valued at $18.50 per unit, for a total purchase price
    of approximately $150.0 million. The Company financed a portion of the
    purchase price with an $80.0 million mortgage loan from Bankers Trust
    Company; this mortgage was subsequently refinanced in October 1998.

(N) Janss Court is a seven-story, 126,000-square foot Class A mixed-use
    building. In addition to 93,000 square feet of retail and office space,
    Janss Court offers 32 apartments for a total of 33,000 rentable square feet
    of residential space.

 (O) The Property is subject to a ground lease agreement. The agreement requires
     annual payments of $115,000 through March 31, 2002 and $121,000 from April
     1, 2002 through March 31, 2007. The lease payment increases every ten years
     thereafter according to a formula based on the Consumer Price Index. The
     ground lease expires on March 31, 2041.

 (P) On January 5, 1998, the Trust purchased for approximately $5.5 million, the
     remaining participation rights in the cash flow and residual value of Tower
     56 from the former participants for 307,692 shares of Common Stock. As a
     result, all of the cash flow and the residual value of Tower 56 inured to
     the Trust. As of January 20, 1998 all of the interest stated above were
     contributed to the Company in exchange for units.

(Q) Rentable square feet includes an adjustment for the interest of a joint
    venture or minority partner. Calculations are based on the partners'
    percentage interest in the cash flows of the Property.

     On March 31, 1998, the Company sold the Dearborn Land (an undeveloped
parcel of land in Chicago that was acquired as part of the acquisition of the
DIHC Portfolio in October 1997) for gross proceeds of approximately $19,000,000,
resulting in a loss of $212,228.

     On April 29, 1998, the Trust sold the Frick Building, located in
Pittsburgh, Pennsylvania, for net proceeds of approximately $26,748. The net
proceeds were contributed to the Company.

     On December 29, 1998, Avenue Associates Limited Partnership sold a
condominium unit in Market Square, located in Washington D.C., for gross
proceeds of $326,154, resulting in a gain of $247,972.

     During 1999, the Company sold thirteen properties for gross proceeds of
$496,530,000 resulting in a net gain of $131,033,847.

                                      F-34
<PAGE>   212
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

2.  PROPERTIES -- (CONTINUED)
     The future minimum lease payments to be received by the Company under
noncancellable operating leases as of December 31, 1999 are as follows (Dollar
amounts in thousands):

<TABLE>
<S>                                                           <C>
2000........................................................  $  396,159
2001........................................................     373,079
2002........................................................     327,096
2003........................................................     269,223
2004........................................................     211,497
Thereafter..................................................     737,345
                                                              ----------
Total.......................................................  $2,314,399
                                                              ==========
</TABLE>

3.  RESTRICTED CASH

     Restricted cash includes security deposits for some of the Company's office
properties and escrow and reserve funds for real estate taxes, property
insurance, capital improvements, tenant improvements and leasing costs. These
funds were established pursuant to certain mortgage and construction financing
arrangements.

     The proceeds from the sales of certain properties during 1999 totaling
approximately $211.5 million, are included in restricted cash pursuant to the
terms of Section 1031 of the Internal Revenue Code of 1986, as amended,
"Exchange of property held for productive use or investment."

4.  INVESTMENT IN UNCONSOLIDATED JOINT VENTURES

     Investment in unconsolidated joint ventures represents the Company's two
investments that are accounted for using the equity method of accounting. The
first investment is the Company's 50.0% interest in a co-tenancy with Crocker
Plaza Company for One Post, a 38-story, Class A office tower in San Francisco,
California. The Company and Crocker co-manage and lease the Property. The second
equity investment is the Company's interest in WCP Services, Inc. The Company
owns 1% of the voting common stock and 100% of the non-voting common stock of
WCP Services, Inc. The remaining shares of voting common stock of WCP Services,
Inc. are owned by certain executive officers of the Company. The Company's
ownership of voting and nonvoting common stock together represents a 95%
economic interest in the earnings of WCP Services, Inc. WCP Services, Inc.
provides property management, development and tenant construction supervision
services to third parties. WCP Services, Inc. also provides tenant construction
supervision services to tenants in Properties owned by the Company.

5.  LONG-TERM DEBT

     The following table sets forth certain information regarding the
consolidated debt obligations of the Company as of December 31, 1999 and 1998,
including mortgage obligations relating to the Properties. All of this debt, is
nonrecourse to the Company. However, notwithstanding the nonrecourse
indebtedness, the

                                      F-35
<PAGE>   213
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

5.  LONG-TERM DEBT -- (CONTINUED)
lender may have the right to recover deficiencies from the Company in certain
circumstances, including fraud, misappropriation of funds and environmental
liabilities (Dollar amounts in thousands).

<TABLE>
<CAPTION>
                                                      INTEREST         MATURITY
            PROPERTY              AMORTIZATION        RATE(A)            DATE         12/31/99    12/31/98
            --------              -------------   ----------------   -------------   ----------  ----------
<S>                               <C>             <C>                <C>             <C>         <C>
FIXED RATE
- --------------------------------
TransPotomac Plaza(B)...........  Interest Only        7.28%          Oct-2000       $   65,000  $   65,000
West Wilshire Office and          25 year
  Medical.......................                       6.90%          Jan-2002           16,926      17,301
Searise Office Tower............  25 year              6.90%          Jan-2002           11,607      11,864
Exposition Centre...............  25 year              6.90%          May-2002            5,081       5,200
Wilshire Palisades..............  22 year              6.70%          Jul-2002           29,047      29,902
110 Atrium Place................  30 year              6.90%          Mar-2004           21,517      21,838
527 Madison Avenue and
  One Lincoln Centre(B).........  Interest only        7.47%          Oct-2004           65,000      65,000
Sixty State Street..............  30 year              6.84%          Jan-2005           85,420      87,627
Island Corporate Center.........  30 year              6.90%          Apr-2005           13,170      13,294
Washington Mutual Tower.........  Interest only        7.53%          Nov-2005           79,100      79,100
Norwest Center..................  Interest only        8.74%          Dec-2005          110,000     110,000
Agoura Hills....................  25 year              6.90%          Dec-2005           12,003      12,328
Janss Court.....................  30 year              6.90%          Dec-2005           18,357      18,723
Bayhill 4, 5, 6 & 7.............  25 year              6.90%          Dec-2006           57,764      59,071
Market Square(C) and 200
  Galleria(B)...................  Interest only        7.54%          Oct-2007          120,000     120,000
Corporate 500 Centre............  25 year              6.66%          Nov-2008           88,424      89,765
188 Embarcadero(D)..............  25 year              7.26%          Aug-2009           15,606       9,135
Centerside II(D)................  25 year              7.26%          Aug-2009           24,254      13,818
700 North Brand(D)..............  25 year              7.26%          Aug-2009           26,938      18,108
Golden Bear Center(D)...........  25 year              7.26%          Aug-2009           20,477      15,753
Bixby Ranch(D)..................  25 year              7.26%          Aug-2009           28,528      20,243
One Memorial Drive(D)...........  25 year              7.26%          Aug-2009           63,119          --
125 Summer Street(E)............  25 year              7.23%          Nov-2009           78,844      50,000
Tower 56(E).....................  25 year              7.23%          Nov-2009           25,024      17,548
Peninsula Office Park 1, 3, 4,
  5, 6, 8
  & 9(E)........................  25 year              7.23%          Nov-2009           88,128      60,242
Embarcadero Place(E)............  25 year              7.23%          Nov-2009           38,149      26,061
201 California Street (E).......  25 year              7.23%          Nov-2009           44,504      33,071
                                                                                     ----------  ----------
Total Fixed Rate Debt...........                      7.31%(F)       7.1 yrs(F)      $1,251,987  $1,069,992
                                                                                     ----------  ----------
VARIABLE RATE
- --------------------------------
Seaport Centre(G)...............  Interest only   LIBOR plus 1.50%    Dec-2000           58,000      58,000
The Pruneyard...................  24 year         LIBOR plus 1.50%    Jul-2000           60,947      49,384
120 Montgomery Street...........  24 year         LIBOR plus 1.40%    Nov-2002           48,160      46,930
Norris Tech Center..............  25 year         LIBOR plus 1.65%    Dec-2003           16,066      16,392
Other loans.....................  Various             Various         Various               245         597
                                                                                     ----------  ----------
Total Variable Rate Debt........                      7.48%(F)       1.5 yrs(F)      $  183,418  $  171,303
                                                                                     ----------  ----------
REPAID DEBT
- --------------------------------
18301 Von Karman(H).............  --                     --              --                  --      10,647
1600 South Main(H)..............  --                     --              --                  --       5,038
Biltmore Lakes(H)...............  --                     --              --                  --      11,468
Belmont Shores(H)...............  --                     --              --                  --       9,839
</TABLE>

                                      F-36
<PAGE>   214
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

5.  LONG-TERM DEBT -- (CONTINUED)

<TABLE>
<CAPTION>
                                                      INTEREST         MATURITY
            PROPERTY              AMORTIZATION        RATE(A)            DATE         12/31/99    12/31/98
            --------              -------------   ----------------   -------------   ----------  ----------
<S>                               <C>             <C>                <C>             <C>         <C>
2677 North Main(H)..............  --                     --              --                  --  $   10,774
2700 Ygnacio Valley Road(H).....  --                     --              --                  --       5,035
Westlake Spectrum(H)............  --                     --              --                  --       3,993
Park Plaza(H)...................  --                     --              --                  --       4,940
Warner Park Center(H)...........  --                     --              --                  --       5,213
429 Santa Monica(H).............  --                     --              --                  --      10,176
Crossroads(H)...................  --                     --              --                  --       7,339
Westlake Spectrum II(H).........  --                     --              --                  --       5,284
Two ADP Plaza(I)................  --                     --              --                  --      13,400
Two Corporate Centre(I).........  --                     --              --                  --      18,600
One & Two Gateway(J)............  --                     --              --                  --       8,679
Scottsdale Centre(J)............  --                     --              --                  --       7,745
66 Bovet(J).....................  --                     --              --                  --       3,939
One Norwest Center(K)...........  --                     --              --                  --      98,252
1300 South El Camino(J).........  --                     --              --                  --       4,007
10 Almaden(L)...................  --                     --              --                  --      33,885
                                  -------------   ----------------     --------      ----------  ----------
Total Repaid Debt...............                                                     $       --  $  278,253
                                                                                     ----------  ----------
Total Debt......................                      7.33%(F)       6.4yrs(F)       $1,435,405  $1,519,548
                                                                                     ==========  ==========
</TABLE>

- ---------------
(A) The interest rate is the stated interest rate (for Company originated debt)
    or the mark to market rate at the time of acquisition (for debt assumed as
    part of an acquisition).

 (B) The three notes arising from the acquisition of several properties in the
     DIHC Portfolio are cross-collateralized, having the effect of forming a
     "collateral pool" for the underlying notes.

(C) The collateral for this loan is a pledge of the $181.0 million first
    mortgage loan on Market Square that the Company purchased from PGGM.

(D) The six notes arising from the restructuring of certain debt with Prudential
    Insurance Company of America and Northwestern Mutual Life Insurance Company
    are cross-collateralized, having the effect of forming a "collateral pool"
    for the underlying notes.

(E) During October 1999 the Company restructured approximately $219.9 million of
    individual property related debt with Northwestern Mutual Life Insurance
    Company. The restructuring involved retiring the individual property related
    debt and creating a single $275.0 million loan which is cross-
    collateralized by six of the original seven properties. The loan has a ten
    year term and bears interest at 7.23%. Upon closing the loan, the lien on 10
    Almaden was released and the property was added to Cornerstone's
    unencumbered pool.

 (F) Weighted-average interest rate and maturity of the Company's long-term
     debt.

(G) On December 15, 1999, through an extension and modification agreement, the
    maturity date of the $58.0 million variable rate debt held on Seaport Centre
    was extended from December 31, 1999 to December 31, 2000. All other terms of
    the note remain unchanged.

(H) These 12 notes were prepaid as part of the Prudential Insurance Company of
    America and Northwestern Mutual Life Insurance Company restructuring, see
    note (D) above. All the notes had a mark to market interest rate of 6.9% and
    maturity dates ranging from April 2000 to March 2003.

 (I) On January 4, 1999, in connection with the Wilson Acquisition, the Company
     prepaid the notes on Two ADP Plaza and Two Corporate Centre.

 (J) These notes were prepaid in conjunction with the sale of these properties.

                                      F-37
<PAGE>   215
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

5.  LONG-TERM DEBT -- (CONTINUED)

(K) The note was assumed by the purchaser as of the date of closing, in
    conjunction with the sale of this property during the fourth quarter.

(L) This note was prepaid as part of the Northwestern Mutual Life Insurance
    Company restructuring, see note (E) above. This note had a mark to market
    interest rate of 6.9% and a maturity of April 2004.

     The combined aggregate amount of maturities for all long-term borrowings
for 2000 through 2004 are $183,947,000, $0, $110,821,000, $16,066,000 and
$86,517,000, respectively.

     Since most of the long-term debt is property related, there are restrictive
covenants that limit the total amount of indebtedness that can be placed on
individual properties.

6.  CREDIT FACILITY

     The Company has a $550.0 million Revolving Credit Facility with a syndicate
of 17 banks led by DB Alex Brown, The Chase Manhattan Bank and Bank of America
for acquisitions and general working capital purposes as well as the issuance of
letters of credit (the "Revolving Credit Facility"). The interest rate on the
facility depends on the Company's ratio of total debt to asset value (as
defined) at the time of borrowing and will be at a spread of 1.10% to 1.40% over
the applicable LIBOR or the Prime Rate at the borrower's option. The letters of
credit will be priced at the applicable Eurodollar credit spread. The Revolving
Credit Facility expires on November 3, 2001. As of December 31, 1999, $329.0
million of the facility was outstanding at a rate of approximately 8.0%. Of this
amount, approximately $250.0 million is fixed with interest rate swaps, which
effectively fix the rate at 6.47%. Beginning January 2000, the rate will be
reduced to 5.41 through the expiration of the swaps in December 2000. The
Revolving Credit Facility contains certain restrictive covenants including: (i)
a limitation on the Company's dividend to 90.0% of funds from operations and
110.0% of funds available for distribution, both as defined in the agreement;
(ii) the percentage of total liabilities to total property asset value (as
defined) cannot exceed 55.0%; (iii) the ratio of adjusted EBITDA to interest
expense may not be less than 2.00 to 1.00 through July 1, 1999 and 2.25 to 1.00
thereafter; (iv) the fixed charge coverage ratio may not be less than 1.75 to
1.00; and (v) the ratio of total property asset value (as defined) to secured
indebtedness may not be less than 2.22 to 1.00. The above terms reflect an
amendment to the Revolving Credit Facility that occurred during 1999. The
amendment allowed the Company to increase its leverage from 55.0% to 60.0% in
(ii) above for a short period, which has since expired. The Company also
increased its ability to enter into mortgage debt under (v) above by decreasing
the ratio from 2.5 to 1.00 to 2.22 to 1.00.

7.  COMMITMENTS AND CONTINGENCIES

     In the ordinary course of business, the Company is subject to tenant and
property related claims and other litigation. It is the opinion of management,
after consultation with outside counsel, that the resolution of these claims
will not have a material adverse effect on the financial position, results of
operations or cash flows of the Company.

     In April 1998, the Company entered into a contract to acquire from the
developer the 928,857 square-foot Piper Jaffray building under construction in
Minneapolis. In November 1999, this contract was amended in connection with a
350,000 square-foot expansion lease with a major tenant of the building. The
contract was amended to provide for a purchase price equal to the costs incurred
in construction and development plus a fixed amount to the developer plus an
additional amount based on the leasing of the building. In addition, at the
Company's election, the closing of the acquisition may occur prior to the
completion of the building, but the developer will remain obligated to complete
the project. Through

                                      F-38
<PAGE>   216
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

7.  COMMITMENTS AND CONTINGENCIES -- (CONTINUED)
December 31, 1999, approximately $109.4 million has been spent on the
construction. The project is scheduled to be completed in the year 2000 and is
approximately 75.0% pre-leased.

8.  PARTNERS' CAPITAL

     As of December 31, 1999, the Trust and its subsidiaries had a 1% general
partnership interest and an approximate 86.1% limited partnership interest in
the Company. The remaining limited partners had an approximate 12.9% interest in
the Company and consist of various individuals and entities that contributed
their properties to the Company in exchange for partnership interest and are
represented by 19,131,785 Units which are exchangeable on a one-for-one basis
into the Trust's Common Shares.

     The 7% Cumulative Convertible Preferred Units are convertible into Common
Stock at $16.50 per share at any time after August 4, 2000.

     On February 6, 1998, the Trust completed a secondary public offering of
14,375,000 shares of Common Stock at a price of $18.25 per share. The shares
were placed in the U.S. through a syndicate of seven investment banks led by
Merrill Lynch & Co. Net proceeds to the Company were approximately $247.9
million (approximately $262.3 million gross proceeds less an underwriting
discount of approximately $13.7 million and expenses of approximately $0.7
million), which were contributed to the Company in exchange for a corresponding
number of Units. The net proceeds were used to repay outstanding borrowings
under the Revolving Credit Facility and for working capital purposes.

9.  UNITHOLDERS' DISTRIBUTIONS

     On December 7, 1998, in connection with the Wilson Acquisition, the Company
declared a distribution of $0.15 per unit to Unitholders of record as of
December 15, 1998 and a distribution of $0.15 per unit to Unitholders of record
as of January 29, 1999. Both distributions were paid on February 26, 1999. A
distribution of $0.30 per unit was declared for the second quarter of 1999 and
paid on May 28, 1999, to Unitholders of record as of April 30, 1999. A
distribution of $0.30 per unit was declared for the third quarter of 1999 and
paid on August 31, 1999, to Unitholders of record as of July 30, 1999. A
distribution of $0.30 per unit was declared on September 28, 1999 for the fourth
quarter of 1999 and paid on November 30, 1999, to Unitholders of record as of
October 29, 1999.

     On August 4, 1999, the Company paid a dividend of $1.155 per share to all
preferred unitholders of record as of July 30, 1999.

10.  EXTRAORDINARY LOSS

     For the year ended December 31, 1999, the Company recorded extraordinary
loss of approximately $10.8 million. This amount represents the prepayment fees
paid in connection with the property debt restructurings that were completed
during June 1999 and October 1999, as well as the write off of any remaining
unamortized premium/discount recorded by the Company related to the retired
debt. See Notes 5 and 16 for more information about the two restructurings.

                                      F-39
<PAGE>   217
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

11.  NET INCOME PER UNIT

     The table below sets forth the calculation of income per Unit for 1999 and
1998 (Dollar amounts in thousands, except per unit amounts):

<TABLE>
<CAPTION>
                                                   1999                          1998
                                        ---------------------------   ---------------------------
                                           BASIC         DILUTED         BASIC         DILUTED
                                        ------------   ------------   ------------   ------------
<S>                                     <C>            <C>            <C>            <C>
Units issuable upon exercise of Trust
  share options.......................            --      3,175,570             --        370,612
Weighted average Units................   148,654,779    148,654,779    103,881,682    103,881,682
                                        ------------   ------------   ------------   ------------
Adjusted weighted average Units.......   148,654,779    151,830,349    103,881,682    104,252,294
                                        ------------   ------------   ------------   ------------
Net income available to Units before
  cumulative effect of a change in
  accounting principle and
  extraordinary loss..................  $    276,666   $    276,666   $     86,327   $     86,327
Income applicable to preferred
  units...............................        (3,500)            --         (3,500)            --
Cumulative effect of a change in
  accounting principle................          (630)          (630)            --             --
Extraordinary loss....................       (10,787)       (10,787)        (4,303)        (4,303)
                                        ------------   ------------   ------------   ------------
Income available to units.............  $    261,749   $    265,249   $     78,524   $     82,024
                                        ------------   ------------   ------------   ------------
Net income available to Units before
  extraordinary items.................  $       1.84   $       1.82   $       0.80   $       0.79
Cumulative effect of a change in
  accounting principle................            --             --             --             --
Extraordinary loss....................         (0.08)         (0.07)         (0.04)         (0.04)
                                        ------------   ------------   ------------   ------------
Income available to units.............  $       1.76   $       1.75   $       0.76   $       0.75
                                        ------------   ------------   ------------   ------------
</TABLE>

     The options issued in February 1998, March 1998, December 1998, January
1999, February 1999 and June 1999 were not included in the calculation of
diluted earnings per Unit as such options were anti-dilutive during the period.
As of December 31, 1999, 1,125,175 Units have been redeemed for shares of the
Trust's Common Stock on a one-for-one basis and 76,647 Units have been redeemed
for approximately $1.2 million in cash.

12.  RETIREMENT AND SHARE OPTION PLANS

     Eligible employees of the Company participate in a noncontributory
age-weighted profit sharing plan. The Company's cash contribution to such plan
was approximately $134,000, and $100,000, for the years ended December 31, 1999
and 1998, respectively.

     Eligible employees of the Company also participate in a 401(k) contributory
savings plan. Under the plan, the Company matches contributions made by eligible
employees based on a percentage of the employee's salary. The Company will match
100% of contributions up to 5.0% of such employee's salary with an annual
maximum matching contribution of $4,000 per employee. The Company's matching
contribution was approximately $654,000, and $69,600, for the years ended
December 31, 1999, and 1998, respectively.

     The Company has adopted the Cornerstone Properties Inc. 1998 Long-Term
Incentive Plan (the "Incentive Plan") to provide incentives to attract and
retain officers and key employees. Under the

                                      F-40
<PAGE>   218
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

12.  RETIREMENT AND SHARE OPTION PLANS -- (CONTINUED)
Incentive Plan as amended and restated on December 14, 1998, the number of
shares available for option grant are approximately 7,400,000. During 1999,
options on approximately 40,000 shares of Common Stock at an exercise price of
$17.25 per share have been granted under the plan. As of December 31, 1999,
10,000 of these shares have been forfeited.

     The following tables summarizes the Trust's stock options and restricted
stock grants for certain officers of the Company as of December 31, 1999, which
is included in the financial statements because any Common Shares issued
pursuant to the officer plan will result in the Company issuing Units to the
Trust on a one-for-one basis:

STOCK OPTIONS

<TABLE>
<CAPTION>
                        OPTIONS GRANTED   EXERCISE PRICE                          OPTIONS     OPTIONS      OPTIONS
    DATE OF GRANT       (NO. OF SHARES)    (PER SHARE)           VESTING         EXERCISED   FORFEITED   EXERCISABLE
    -------------       ---------------   --------------   -------------------   ---------   ---------   -----------
<S>                     <C>               <C>              <C>                   <C>         <C>         <C>
August, 1995..........  637,500               $14.30       33.3%/yr, 10yr term    75,000            0      562,500
October, 1995.........  150,000               $14.30       33.3%/yr, 10yr term    10,500            0      139,500
March, 1997...........  880,000               $14.50       33.3%/yr, 10yr term    52,000            0      534,666
November, 1997........  70,000                $18.44       33.3%/yr, 10yr term         0            0       46,667
February, 1998........  70,000                $18.13       33.3%/yr, 10yr term         0       46,667       23,333
February, 1998........  595,000               $18.25       33.3%/yr, 10yr term         0       26,668      198,333
March, 1998...........  200,000               $18.25       33.3%/yr, 10yr term         0      133,334       66,666
December, 1998........  3,000,000             $17.25       33.3%/yr, 10yr term         0       34,533      978,800
January, 1999.........  20,000                $17.25       33.3%/yr, 10yr term         0            0            0
February, 1999........  10,000                $17.25       33.3%/yr, 10yr term         0       10,000            0
June, 1999............  10,000                $17.25       33.3%/yr, 10yr term         0            0            0
</TABLE>

     The weighted average fair value of options granted during 1999 and 1998 was
$0.33 per share and $0.28 per share, respectively. The weighted average Life of
options outstanding at December 31, 1999 was approximately 7.6 years.

RESTRICTED STOCK GRANTS

<TABLE>
<CAPTION>
                       VALUE OF GRANT    SHARES INITIALLY                          SHARES
                            DATE             GRANTED        SHARES FORFEITED     OUTSTANDING      SHARES VESTED    VESTING(A)
    DATE OF GRANT       (PER SHARES)     (NO. OF SHARES)     (NO. OF SHARE)    (NO. OF SHARES)   (NO. OF SHARES)   SEE NOTES
    -------------      --------------    ----------------   ----------------   ---------------   ---------------   ----------
<S>                    <C>               <C>                <C>                <C>               <C>               <C>
August, 1995.........      $14.30            186,713             19,091            167,622           89,396              (B)
March, 1997..........      $16.40            100,000                  0            100,000           26,666              (C)
November, 1997.......      $18.44             12,500                  0             12,500            3,333              (D)
March, 1998..........      $18.13             12,500             10,833              1,667            1,667              (E)
March, 1998..........      $18.25             19,178                  0             19,178           19,178              (F)
February, 1999.......      $15.50            113,500              1,700            111,800            1,400              (G)
</TABLE>

- ---------------
 (A) Deferred compensation of approximately $5,600,000 is being amortized
     according to the respective amortization schedule for each vesting period
     noted below, with the unamortized balance shown as a deduction from
     stockholders' equity. Regular distributions are paid on restricted stock.

 (B) The grant will fully vest with respect to 13.333% on June 30, 1996, 1997,
     1998, 1999 and with respect to 46.668% on June 30, 2000.

 (C) The grant will fully vest with respect to 13.333% on June 30, 1998, 1999,
     2000, 2001 and with respect to 46.668% on June 30, 2002.

                                      F-41
<PAGE>   219
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

12.  RETIREMENT AND SHARE OPTION PLANS -- (CONTINUED)

 (D) The grant will fully vest with respect to 13.333% on June 30, 1998, 1999,
     2000, 2001 and with respect to 46.668% on June 30, 2002.

 (E) The grant will fully vest with respect to 13.333% on March 15, 1999, 2000,
     2001, 2002 and with respect to 46.668% on March 15, 2003.

 (F) The initial grant was to vest with respect to 13.333% on March 15, 1999,
     2000, 2001, 2002 and with respect to 46.668% on March 15, 2003. Pursuant to
     the terms of a separation agreement, the vesting with respect to 16,621
     shares was accelerated to fully vest on December 31, 1999.

(G) The grant will fully vest on February 1, 2004. Pursuant to the terms of
    certain separation agreements, the vesting with respect to 1,400 shares was
    accelerated to fully vest on July 1, 1999.

     The Trust has adopted the disclosure-only provision of Statement of
Financial Accounting Standard No. 123, "Accounting for Stock-Based Compensation"
("SFAS 123"). Accordingly, no compensation cost has been recognized for the
options described above since the exercise price equaled the fair value at the
grant date. Had compensation cost for these options been determined based on the
fair value at the grant date consistent with the provisions of SFAS 123, the
Trust's net income and net income per common share would have been reduced to
the following pro forma amounts (Dollar amounts in thousands, except per share
amounts):

<TABLE>
<CAPTION>
                                                           BASIC           DILUTED
                                                       NET INCOME PER   NET INCOME PER
                                        NET INCOME      COMMON SHARE     COMMON SHARE
                                        ----------     --------------   --------------
<S>                                   <C>              <C>              <C>
Year ended December 31, 1999........     $229,622          $1.76            $1.73
Year ended December 31, 1998........     $ 81,561          $0.73            $0.73
</TABLE>

     The Company has computed the value of all stock options using the
Black-Scholes option pricing model with the following weighted average
assumptions:

<TABLE>
<CAPTION>
                        ASSUMPTIONS                           1999      1998
                        -----------                          -------   -------
<S>                                                          <C>       <C>
Risk-free interest rate....................................     5.31%     5.31%
Assumed dividend yield.....................................     7.50%     7.50%
Expected term..............................................  6 years   6 years
Assumed volatility.........................................    10.00%    10.00%
</TABLE>

13.  CONCENTRATION OF RISK

     Approximately 5.8 million of the Company's 17 million rentable square feet
is located in the San Francisco metropolitan market, accounting for
approximately 29% of the Company's total assets at December 31, 1999. In
addition, five of the Company's 83 office Properties are located in the Downtown
Boston market, accounting for approximately 19.4% of the Company's office and
parking revenues for the year ended December 31, 1999. This concentration of
assets makes the Company particularly vulnerable to adverse changes in economic
conditions in the San Francisco and Boston metropolitan areas. A significant
decline in these economic conditions could have a material adverse effect on the
Company.

     Norwest Corporation and its subsidiary, Norwest Bank Denver N.A., tenants
of the Company, provided approximately 6.2%, and 9.5% of office and parking
rental income for the years ended December 31, 1999 and 1998, respectively.
Included in deferred tenant receivables is approximately $34.8 million and $33.9
million due from Norwest Corporation at December 31, 1998 and 1997,

                                      F-42
<PAGE>   220
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

13.  CONCENTRATION OF RISK -- (CONTINUED)
respectively. As a result of the sale of the Company's property located in
Denver during the fourth quarter of 1999, the concentration of revenue received
from this tenant will be significantly reduced.

14.  RELATED PARTY TRANSACTIONS

     The Company has entered into $250.0 million of mortgage debt with one of
the Trust's major stockholders, PGGM, as further described in Note 5.

     In connection with the Wilson Acquisition, certain third-party services
business of WW&A was acquired by WCP Services, Inc., a Delaware corporation
("WCP Services"). The Company owns 100% of the non-voting common stock and 1% of
the voting common stock of WCP Services. Mr. Wilson and Mr. Moody each own 49.5%
of the voting common stock of WCP Services. To fund the purchase of such shares
of voting common stock, the Company loaned $178,750 to each of Mr. Wilson and
Mr. Moody, all of which remained outstanding as of December 31, 1999. The notes
accrue interest at a rate equal to 140 basis points plus the one-year London
Interbank Offered Rate, which rate is adjusted annually. The notes are due and
payable on or before December 16, 2008. In connection with the EOP Merger
Agreement, Messrs. Wilson and Moody entered into an agreement to sell their
voting common stock of WCP Services to EOP at a purchase price of $200,000 each.

15.  FAIR VALUE OF FINANCIAL INSTRUMENTS

     The Company is required to disclose the fair value of financial instruments
for which it is practicable to estimate that value. The Company determines the
fair value based on discounting future cash flows at a rate that approximates
the Company's effective current borrowing rate (see also Note 5). For the year
ended December 31, 1999 and 1998, the fair value of the Company's long term debt
was approximately $1,367,000 million and $1,542,000 million, respectively.

16.  SUPPLEMENTAL CASH FLOW INFORMATION

     Cash paid for interest was approximately $138,375 million and $60,992
million for the years ended December 31, 1999 and 1998, respectively.

NON-CASH INVESTING AND FINANCING ACTIVITIES

     On January 20, 1998, the Trust converted its corporate structure into an
umbrella limited partnership REIT ("UPREIT"). Under the UPREIT structure, the
Trust assigned substantially all of its interest in its properties and
substantially all of its operations to the Company.

     On January 28, 1998, the Company purchased Corporate 500 Centre. As part of
the total purchase price of approximately $150.0 million, the Company issued
822,794 Units valued at $18.50 per unit.

     On April 28, 1998, the Company purchased One Memorial Drive. As part of the
total purchase price of approximately $112.5 million, the Trust issued 3,428,571
shares of common stock and the Company issued 1,657,426 Units, both valued at
$17.50.

     On June 3, 1998, the Company purchased 201 California Street and Wilshire
Palisades. As part of the total purchase price for the Properties of
approximately $121.5 million, the Company assumed $64.6 million in debt and
issued 1,665,663 Units valued at $17.50 per unit.

     On September 25, 1998, in conjunction with the refinancing of the One
Norwest Center mortgage, the Company incurred an extraordinary loss of
approximately $2,269,000, which represents the

                                      F-43
<PAGE>   221
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

16.  SUPPLEMENTAL CASH FLOW INFORMATION -- (CONTINUED)
unamortized deferred financing costs and prepayment fees on the previous One
Norwest Center mortgage at the time of the refinancing.

     On October 9, 1998, in conjunction with the refinancing of the Corporate
500 Centre mortgage, the Company incurred an extraordinary loss of $354,717,
which represents the unamortized deferred financing costs on the previous
Corporate 500 Centre mortgage at the time of the refinancing.

     On November 3, 1998, the Company obtained a $550.0 million Revolving Credit
Facility from a syndicate of 17 banks led by Bankers Trust Company, The Chase
Manhattan Bank and NationsBank. In conjunction with obtaining this new Revolving
Credit Facility, the Company incurred an extraordinary loss of $1,680,016, which
represents the unamortized deferred financing costs related to the previous
$350.0 million facility, which was extinguished at the time that the new
Revolving Credit Facility was obtained.

     On December 16, 1998, the Company consummated the Wilson Acquisition for a
purchase price of approximately $1.8 billion, consisting of approximately 14.9
million shares of the Trust's Common Stock valued at $17.25 per share (recorded
at $16.25 per share for GAAP purposes), approximately 16.2 million Units valued
at $17.25 per unit (recorded at $16.25 for GAAP purposes), approximately $465.0
million in cash and the assumption of approximately $760.0 million of property
and construction related debt (recorded at $773.7 million for GAAP purposes).
The Company also recorded a minority interest of $241.0 million in connection
with this acquisition.

     During the first quarter of 1999, pursuant to the requirements of SOP 98-5
(as defined in Note 1), the Company wrote off all unamortized organizational
costs and recorded a cumulative effect of a change in accounting principle of
$630,044.

     On February 1, 1999, the Trust issued 113,500 shares of restricted stock
valued at $15.50 per share to certain employees of the Company. Units were also
issued to the Trust on a one-for-one basis.

     On June 23, 1999, in conjunction with the restructuring of property-related
debt with Prudential Insurance Company of America and Northwestern Mutual Life
Insurance Company, the Company incurred an extraordinary loss of approximately
$3,355,000, of which approximately $1,560,000 represents the unamortized
premium/discounts associated with various debt instruments that were assumed as
part of the Wilson Acquisition. See Note 5 for more information about this
restructuring.

     During 1999, 1,700 shares of the Trust's restricted Common Stock issued to
certain employees of the Company were forfeited as a result of their separation
from the Company.

     On July 30, 1999, 562,588 Units were redeemed for shares of the Trust's
Common Stock on a one-for-one basis.

     On August 3, 1999, 562,587 Units were redeemed for shares of the Trust's
Common Stock on a one-for-one basis.

     On August 17, 1999, the Trust reacquired 10,833 shares of restricted Common
Stock as a result of the forfeiture of these shares by a certain employee of the
Company.

     On October 6, 1999, in conjunction with the restructuring of
property-related debt with Northwestern Mutual Life Insurance Company, the
Company incurred an extraordinary loss of approximately $7,432,000, of which
approximately $2,551,000 represents the unamortized premium/discounts associated
with various debt instruments. See Note 5 for more information about this
restructuring.

                                      F-44
<PAGE>   222
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

16.  SUPPLEMENTAL CASH FLOW INFORMATION -- (CONTINUED)
     On December 10, 1999, in conjunction with the sale of One Norwest Center in
Denver, Colorado, $97.3 million of outstanding debt was assumed by the
purchaser.

     On December 31, 1999 an affiliate of the Trust, Corpro Real Estate
Management Company, Inc., was dissolved. The remaining assets were contributed
to the Company.

17.  SEGMENT REPORTING

     The Company has one reportable segment - real estate. The Company does not
have any foreign operations. The accounting policies of the segment are the same
as those described in Note 1. See Note 13 for information regarding
concentration of risk.

     The Company evaluates performance based on net operating income from the
individual properties in the segment. (Dollar amounts in thousands)

<TABLE>
<CAPTION>
                                                                   CORPORATE &    COMPANY
                                                   TOTAL SEGMENT    OTHER(A)       TOTAL
                                                   -------------   -----------   ----------
<S>                                                <C>             <C>           <C>
Total revenues(B):
  1999...........................................   $  611,657      $   4,659    $  616,316
  1998...........................................      336,922          2,415       339,337
Total operating and Interest expenses(C):
  1999...........................................   $  212,686      $ 155,517    $  368,203
  1998...........................................      112,271         79,136       191,407
Net operating income(D):
  1999...........................................   $  398,971      $(150,858)   $  248,113
  1998...........................................      224,651        (76,721)      147,930
Total long-lived assets(E):
  1999...........................................   $3,770,924      $  66,064    $3,836,988
  1998...........................................    4,137,302         54,782     4,192,084
Total assets:
  1999...........................................   $3,776,765      $ 393,463    $4,170,228
  1998...........................................    4,198,099         83,559     4,281,658
</TABLE>

- ---------------
 (A) Corporate and Other represents all corporate-level items (including
     interest income, interest expense and general and administrative expenses)
     as well as intercompany eliminations necessary to reconcile to consolidated
     Company totals.

 (B) Total revenues represents all revenues during the period (including the
     Company's earnings in real estate joint ventures). All interest income is
     excluded from the segment amounts and is classified in Corporate and Other
     for all periods.

 (C) Total operating and interest expenses represents the sum of building
     operating expenses, real estate taxes, interest expense and general and
     administrative expenses. All interest expense (including property level
     mortgages) is excluded from the segment amounts and is classified in
     Corporate and Other for all periods. Amounts presented exclude depreciation
     and amortization of $96,726,000 and $57,031,000 in 1999 and 1998,
     respectively.

(D) Net operating income represents total revenues (as defined in note (B)
    above) less total operating and interest expense (as defined in note (C)
    above) for the period.

                                      F-45
<PAGE>   223
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

17.  SEGMENT REPORTING -- (CONTINUED)

 (E) Long-lived assets is composed of total rentals property, investments in
     joint ventures, other deferred costs, deferred tenant receivables and
     certain other assets.

18.  SUBSEQUENT EVENTS

     On January 20, 2000, the Company declared a distribution of $0.31 per unit
paid on February 29, 2000, Unitholders of record as of January 31, 2000.

     On January 21, 2000, the Company purchased Wells Fargo Center in
Sacramento, California. This property contains approximately 502,000 rentable
square feet. The total purchase price for the Property was approximately $130.0
million, consisting of approximately $128.0 million in cash of which $104.8
million was 1031 exchange funds (see Note 3) and approximately $2.0 million of
which was paid in Units valued at $17.25 per unit.

     On March 8, 2000, the Company declared a distribution of $0.20 per unit
paid to all unitholders on April 14, 2000.

     On March 15, 2000, the Company sold it interests in a property for gross
proceeds of $14,425,000 located in East Bay, California. The property was
acquired as part of the Wilson Acquisition in December 1998.

     On March 23, 2000, the Company sold its interest in a Property located in
East Bay, California for gross proceeds of $12,800,000. The Property had been
acquired as part of the Wilson Acquisition in December 1998.

     On March 30, 2000, 101,050 Units were redeemed for shares of the Trust's
Common Stock on a one-for-one basis.

                                      F-46
<PAGE>   224

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                                  SCHEDULE III
                               DECEMBER 31, 1999
<TABLE>
<CAPTION>
       COLUMN A            COLUMN B             COLUMN C               COLUMN D                     COLUMN E
- -----------------------  ------------    -----------------------   ----------------   ------------------------------------
                                                                   COST CAPITALIZED
                                                                    SUBSEQUENT TO        GROSS AMOUNT AT WHICH CARRIED
                                         INITIAL COST TO COMPANY     ACQUISITION               AT CLOSE OF PERIOD
                                         -----------------------   ----------------   ------------------------------------
                                                     BUILDING &         LAND &                    BUILDING &
DESCRIPTION              ENCUMBRANCES      LAND     IMPROVEMENTS     IMPROVEMENTS       LAND     IMPROVEMENTS     TOTAL
- -----------              ------------    --------   ------------   ----------------   --------   ------------   ----------
                                                           (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>             <C>        <C>            <C>                <C>        <C>            <C>
Boston, Massachusetts
 Sixty State Street....      $85,420     $     --    $  221,568        $  6,813       $     --    $  228,381    $  228,381
 500 Boylston Street...                    45,132       181,574            (112)        45,132       181,462       226,594
 222 Berkeley Street...                    29,262       118,180             284         29,262       118,464       147,726
 125 Summer Street.....       78,844       15,750        89,250           7,867         15,750        97,117       112,867
 One Memorial Drive....       63,119       22,500        90,873              (6)        22,500        90,867       113,367
San Mateo County,
 California
 Bayhill (4
   buildings)..........       57,764       26,353       105,412           2,166         26,353       107,578       133,931
 Peninsula Office Park
   (7 buildings).......       88,128       25,426       101,705           2,885         25,426       104,590       130,016
 Seaport Centre........       58,000       23,530        94,119           5,259         23,530        99,378       122,908
 Bay Park Plaza (2
   buildings)..........                    13,139        52,556             244         13,139        52,800        65,939
 One Bay Plaza.........                     9,125        36,499           1,165          9,125        37,664        46,789
East Bay, California
 Corporate Centre (2
   buildings)..........                     9,808        39,233             637          9,808        39,870        49,678
 ADP Plaza (2
   buildings)..........                    10,278        41,110             502         10,278        41,612        51,890
 PeopleSoft Plaza......                    10,025        40,100             644         10,025        40,744        50,769
 Norris Tech Center (3
   buildings)..........       16,066        7,223        28,893             379          7,223        29,272        36,495
 Golden Bear Center....       20,477        6,426        25,705             250          6,426        25,955        32,381
 2700 Ygnacio Valley
   Road................                     2,375         9,498             192          2,375         9,690        12,065
 Park Plaza............                     2,673        10,693             323          2,673        11,016        13,689
 1600 South Main.......                     2,501        10,003             175          2,501        10,178        12,679
Atlanta, Georgia
 191 Peachtree
   Street..............                    40,110       228,962           4,575         40,110       233,537       273,647
 200 Galleria..........      120,000(B)    11,994        48,443           3,621         12,726        51,332        64,058
Seattle, Washington
 Washington Mutual
   Tower (3
   buildings)..........       79,100       21,167        43,153         150,354         21,173       193,501       214,674
 110 Atrium Place......       21,517        7,810        31,242             357          7,810        31,599        39,409
 Island Corporate
   Center..............       13,170        3,751        15,004             325          3,751        15,329        19,080
Santa Clara, California
 Pruneyard Office (3
   buildings)..........       60,947       11,896        47,583          13,162         11,896        60,745        72,641
 10 Almaden............                    14,306        57,223             314         14,306        57,537        71,843
 Pruneyard Shopping
   Center..............                     8,491        33,966           1,053          8,491        35,019        43,510
 Embarcadero Place (4
   buildings)..........       38,149       11,728        46,913             (63)        11,728        46,850        58,578
 Pruneyard Inn (C).....                     3,057        12,228           3,126          3,057        15,354        18,411

<CAPTION>
       COLUMN A            COLUMN F      COLUMN G      COLUMN H        COLUMN I
- -----------------------  ------------   -----------   -----------   ---------------

                                                                     LIFE ON WHICH
                                                                    DEPRECIATION IN
                                        (UNAUDITED)   (UNAUDITED)    LATEST INCOME
                         ACCUMULATED       YEAR          DATE        STATEMENTS IS
DESCRIPTION              DEPRECIATION   CONSTRUCTED    ACQUIRED       COMPUTED(A)
- -----------              ------------   -----------   -----------   ---------------
                                       (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>            <C>           <C>           <C>
Boston, Massachusetts
 Sixty State Street....   $ (11,312)           1979    12/31/97            40
 500 Boylston Street...      (9,949)           1988    10/27/97            40
 222 Berkeley Street...      (6,515)           1991    10/27/97            40
 125 Summer Street.....     (12,611)           1989     11/1/95            40
 One Memorial Drive....      (3,812)           1985     4/28/98            40
San Mateo County,
 California
 Bayhill (4
   buildings)..........      (2,836)      1982-1987    12/16/98            40
 Peninsula Office Park
   (7 buildings).......      (2,759)      1971-1998    12/16/98            40
 Seaport Centre........      (2,772)           1988    12/16/98            40
 Bay Park Plaza (2
   buildings)..........      (1,403)      1985-1998    12/16/98            40
 One Bay Plaza.........        (997)           1979    12/16/98            40
East Bay, California
 Corporate Centre (2
   buildings)..........      (1,066)      1985-1987    12/16/98            40
 ADP Plaza (2
   buildings)..........      (1,110)      1987-1989    12/16/98            40
 PeopleSoft Plaza......      (1,069)           1984    12/16/98            40
 Norris Tech Center (3
   buildings)..........        (761)      1984-1998    12/16/98            40
 Golden Bear Center....        (702)           1986    12/16/98            40
 2700 Ygnacio Valley
   Road................        (155)           1984    12/16/98            40
 Park Plaza............        (321)           1986    12/16/98            40
 1600 South Main.......        (271)           1983    12/16/98            40
Atlanta, Georgia
 191 Peachtree
   Street..............     (13,469)           1991    10/27/97            40
 200 Galleria..........      (3,146)           1985    10/27/97            40
Seattle, Washington
 Washington Mutual
   Tower (3
   buildings)..........     (82,749)           1988      5/1/88            40
 110 Atrium Place......        (839)           1981    12/16/98            40
 Island Corporate
   Center..............        (404)           1987    12/16/98            40
Santa Clara, California
 Pruneyard Office (3
   buildings)..........      (1,517)      1971-1999    12/16/98            40
 10 Almaden............      (1,510)           1989    12/16/98            40
 Pruneyard Shopping
   Center..............        (922)          1970s    12/16/98            40
 Embarcadero Place (4
   buildings)..........      (1,221)           1984    12/16/98            40
 Pruneyard Inn (C).....        (339)           1989    12/16/98            40
</TABLE>

                                      F-47
<PAGE>   225
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                          SCHEDULE III -- (CONTINUED)
                               DECEMBER 31, 1999
<TABLE>
<CAPTION>
       COLUMN A            COLUMN B             COLUMN C               COLUMN D                     COLUMN E
- -----------------------  ------------    -----------------------   ----------------   ------------------------------------
                                                                   COST CAPITALIZED
                                                                    SUBSEQUENT TO        GROSS AMOUNT AT WHICH CARRIED
                                         INITIAL COST TO COMPANY     ACQUISITION               AT CLOSE OF PERIOD
                                         -----------------------   ----------------   ------------------------------------
                                                     BUILDING &         LAND &                    BUILDING &
DESCRIPTION              ENCUMBRANCES      LAND     IMPROVEMENTS     IMPROVEMENTS       LAND     IMPROVEMENTS     TOTAL
- -----------              ------------    --------   ------------   ----------------   --------   ------------   ----------
                                                           (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>             <C>        <C>            <C>                <C>        <C>            <C>
San Francisco,
 California
 120 Montgomery
   Street..............       48,160       16,427        65,709           2,958         16,427        68,667        85,094
 201 California
   Street..............       44,504       11,350        46,040           2,007         11,350        48,047        59,397
 188 Embarcadero.......       15,606        4,718        18,871             399          4,718        19,270        23,988
Minneapolis, Minnesota
 Norwest Center........      110,000       18,000        33,613         152,888         18,000       186,501       204,501
Washington, D.C./
 Alexandria, Virginia
 Market Square (2
   buildings)..........             (B)    50,199       201,084           2,964         50,199       204,048       254,247
 99 Canal Center.......                     4,551        18,380           1,574          4,551        19,954        24,505
 TransPotomac Plaza
   5...................       65,000(B)     2,124         8,577           1,000          2,124         9,577        11,701
 11 Canal Center.......                     2,326         9,394             500          2,326         9,894        12,220
Suburban Chicago,
 Illinois
 Corporate 500 Centre
   (4 buildings).......       88,424       30,000       120,163           3,456         30,000       123,619       153,619
 One Lincoln Centre....       65,000(B)     2,192        47,758           4,302          2,192        52,060        54,252
Santa Monica/West Los
 Angeles, California
 West Wilshire (2
   buildings)..........       16,926        7,492        29,970             629          7,492        30,599        38,091
 Wilshire Palisades....       29,047       12,650        52,247           1,291         12,650        53,538        66,188
 Janss Court (D).......       18,357        7,274        29,098             147          7,274        29,245        36,519
 Searise Office
   Tower...............       11,607        6,043        24,172             347          6,043        24,519        30,562
 Commerce Park.........                     2,653        10,613             149             --        13,415        13,415
 429 Santa Monica......                     3,899        15,595             317          3,899        15,912        19,811
Orange County,
 California
 Bixby Ranch...........       28,528        9,681        38,723             300          9,681        39,023        48,704
 18301 Von Karman......                     8,052        32,206           2,224          8,052        34,430        42,482
 2677 South Main.......                     5,696        22,786           1,571          5,696        24,357        30,053
San Diego, California
 Centerside II.........       24,254        7,524        30,094             609          7,523        30,703        38,226
 Crossroads............                     3,207        12,828             222          3,207        13,050        16,257
Los Angeles, California
 700 North Brand.......       26,938        8,112        32,450             145          8,112        32,595        40,707
 Warner Park Center....                     1,746         6,986             123          1,746         7,109         8,855
New York City, New York
 527 Madison Avenue....             (B)    21,440        46,643           2,627         21,440        49,270        70,710
 Tower 56..............       25,024        5,528        25,203           9,434          5,528        34,637        40,165
Conejo Valley
 (Ventura), California
 Westlake Spectrum (2
   buildings)..........                     3,510        14,038             177          3,510        14,215        17,725
 Agoura Hills..........       12,003        3,821        15,284             241          3,821        15,525        19,346

<CAPTION>
       COLUMN A            COLUMN F      COLUMN G      COLUMN H        COLUMN I
- -----------------------  ------------   -----------   -----------   ---------------

                                                                     LIFE ON WHICH
                                                                    DEPRECIATION IN
                                        (UNAUDITED)   (UNAUDITED)    LATEST INCOME
                         ACCUMULATED       YEAR          DATE        STATEMENTS IS
DESCRIPTION              DEPRECIATION   CONSTRUCTED    ACQUIRED       COMPUTED(A)
- -----------              ------------   -----------   -----------   ---------------
                                       (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>            <C>           <C>           <C>
San Francisco,
 California
 120 Montgomery
   Street..............      (1,846)           1955    12/16/98            40
 201 California
   Street..............      (1,845)           1969      6/3/98            40
 188 Embarcadero.......        (504)           1980    12/16/98            40
Minneapolis, Minnesota
 Norwest Center........     (84,164)           1988      7/1/88            40
Washington, D.C./
 Alexandria, Virginia
 Market Square (2
   buildings)..........      (6,142)           1990     11/1/98            40
 99 Canal Center.......      (1,089)           1986    10/27/97            40
 TransPotomac Plaza
   5...................        (544)           1983    10/27/97            40
 11 Canal Center.......        (573)           1986    10/27/97            40
Suburban Chicago,
 Illinois
 Corporate 500 Centre
   (4 buildings).......      (5,958)      1986/1990     1/28/98            40
 One Lincoln Centre....      (4,361)           1986     11/8/96            40
Santa Monica/West Los
 Angeles, California
 West Wilshire (2
   buildings)..........        (411)      1960-1976    12/16/98            40
 Wilshire Palisades....      (2,155)           1981      6/3/98            40
 Janss Court (D).......        (772)           1989    12/16/98            40
 Searise Office
   Tower...............        (657)           1975    12/16/98            40
 Commerce Park.........        (349)           1977    12/16/98            40
 429 Santa Monica......        (411)           1982    12/16/98            40
Orange County,
 California
 Bixby Ranch...........      (1,024)           1987    12/16/98            40
 18301 Von Karman......        (971)           1991    12/16/98            40
 2677 South Main.......        (681)           1987    12/16/98            40
San Diego, California
 Centerside II.........        (803)           1987    12/16/98            40
 Crossroads............        (358)           1983    12/16/98            40
Los Angeles, California
 700 North Brand.......        (852)           1981    12/16/98            40
 Warner Park Center....        (183)           1986    12/16/98            40
New York City, New York
 527 Madison Avenue....      (3,762)           1986     2/14/97            40
 Tower 56..............      (3,501)           1983     4/24/96            40
Conejo Valley
 (Ventura), California
 Westlake Spectrum (2
   buildings)..........        (367)           1990    12/16/98            40
 Agoura Hills..........        (417)           1987    12/16/98            40
</TABLE>

                                      F-48
<PAGE>   226
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                          SCHEDULE III -- (CONTINUED)
                               DECEMBER 31, 1999
<TABLE>
<CAPTION>
       COLUMN A            COLUMN B             COLUMN C               COLUMN D                     COLUMN E
- -----------------------  ------------    -----------------------   ----------------   ------------------------------------
                                                                   COST CAPITALIZED
                                                                    SUBSEQUENT TO        GROSS AMOUNT AT WHICH CARRIED
                                         INITIAL COST TO COMPANY     ACQUISITION               AT CLOSE OF PERIOD
                                         -----------------------   ----------------   ------------------------------------
                                                     BUILDING &         LAND &                    BUILDING &
DESCRIPTION              ENCUMBRANCES      LAND     IMPROVEMENTS     IMPROVEMENTS       LAND     IMPROVEMENTS     TOTAL
- -----------              ------------    --------   ------------   ----------------   --------   ------------   ----------
                                                           (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>             <C>        <C>            <C>                <C>        <C>            <C>
Other
 U.S. West (Murray,
   Utah)...............                     3,311        13,245             185          3,311        13,430        16,741
 Exposition Centre
   (Sacramento, CA)....        5,081        1,772         7,089             209          1,772         7,298         9,070
Projects under
 development...........           --       46,720        10,103           6,309         46,132        17,000        63,132
                         -----------     --------    ----------        --------       --------    ----------    ----------
Grand Total............   $1,435,160     $707,854    $2,900,650        $405,795       $705,350    $3,308,948    $4,014,298
                         ===========     ========    ==========        ========       ========    ==========    ==========

<CAPTION>
       COLUMN A            COLUMN F      COLUMN G      COLUMN H        COLUMN I
- -----------------------  ------------   -----------   -----------   ---------------

                                                                     LIFE ON WHICH
                                                                    DEPRECIATION IN
                                        (UNAUDITED)   (UNAUDITED)    LATEST INCOME
                         ACCUMULATED       YEAR          DATE        STATEMENTS IS
DESCRIPTION              DEPRECIATION   CONSTRUCTED    ACQUIRED       COMPUTED(A)
- -----------              ------------   -----------   -----------   ---------------
                                       (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>            <C>           <C>           <C>
Other
 U.S. West (Murray,
   Utah)...............        (375)           1985    12/16/98            40
 Exposition Centre
   (Sacramento, CA)....        (222)           1984    12/16/98            40
Projects under
 development...........          --             N/A          --           N/A
                          ---------     -----------    --------           ---
Grand Total............   $(291,834)
                          =========
</TABLE>

- ---------------
(A) The life to compute depreciation on Buildings is 40 years. The life to
    compute depreciation on Building Improvements is 3 to 40 years.

(B) The three notes arising from the acquisition of several properties from PGGM
    (a major stockholder and related party) are cross-collateralized, having the
    effect of forming a "collateral pool" for the underlying notes. In addition,
    the $181.0 million first mortgage loan on Market Square, which the Company
    purchased from PGGM in 1997, has been pledged as collateral for the $120.0
    million 200 Galleria loan.

(C) The Pruneyard Inn is a 172-room hotel.

(D) In addition to 92,000 square feet of retail and office space, Janss Court
    contains 32 apartments comprising 33,000 rentable square feet of residential
    space.

                                      F-49
<PAGE>   227

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                                  SCHEDULE III
                               DECEMBER 31, 1999
                                  (CONTINUED)

RECONCILIATION OF "REAL ESTATE AND ACCUMULATED DEPRECIATION"

<TABLE>
<CAPTION>
                                                                 1999          1998
                                                              ----------    ----------
<S>                                                           <C>           <C>
INVESTMENT IN REAL ESTATE AND ASSETS HELD FOR SALE
Balance, beginning of period................................  $4,340,449    $1,918,746
  Additions during period:
     Acquisitions...........................................      38,437     2,410,427
     Improvements...........................................      14,904        30,690
  Deductions during period:
     Properties disposed of.................................    (358,670)      (19,414)
     Retirements and writeoffs..............................     (20,822)           --
                                                              ----------    ----------
Balance, end of period......................................  $4,014,298    $4,340,449
                                                              ==========    ==========
ACCUMULATED DEPRECIATION
Balance, beginning of period................................  $  288,448    $  231,421
  Additions during period:
     Depreciation...........................................      96,726        57,031
  Deductions during period:
     Properties disposed of.................................     (73,131)
     Retirements and writeoffs..............................     (20,209)           (4)
                                                              ----------    ----------
                                                              $  291,834    $  288,448
                                                              ==========    ==========
</TABLE>

                                      F-50
<PAGE>   228

                                                                         ANNEX A

                          AGREEMENT AND PLAN OF MERGER
                                     AMONG
                        EQUITY OFFICE PROPERTIES TRUST,
                       EOP OPERATING LIMITED PARTNERSHIP,
                          CORNERSTONE PROPERTIES INC.
                                      AND
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP
                         DATED AS OF FEBRUARY 11, 2000
<PAGE>   229

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                           PAGE
                                                                           ----
<C>          <S>                                                           <C>
ARTICLE 1    THE MERGERS.................................................   A-2
    1.1      Election by Limited Partners in Cornerstone Partnership to
             Exercise the Redemption Right; The Partnership Merger.......   A-2
    1.2      The Merger..................................................   A-3
    1.3      Closing.....................................................   A-3
    1.4      Effective Time..............................................   A-3
    1.5      Effect of Partnership Mergers on Agreement of Limited
             Partnership.................................................   A-4
    1.6      Effect of Merger on Declaration of Trust and Bylaws.........   A-4
    1.7      Trustees of EOP.............................................   A-4
    1.8      Effect on Shares............................................   A-5
    1.9      Effect on Partnership Interests.............................   A-5
   1.10      Exchange Ratios and Other Merger Consideration..............   A-5
   1.11      Election by Holders of Cornerstone Common Stock to Receive
             EOP Common Shares or Cash...................................   A-6
   1.12      Proration...................................................   A-7
   1.13      Partner Approval............................................   A-8
   1.14      No Appraisal Rights.........................................   A-8
   1.15      Exchange of Certificates; Pre-Closing Dividends; Fractional
             Shares......................................................   A-8
ARTICLE 2    REPRESENTATIONS AND WARRANTIES OF CORNERSTONE AND
             CORNERSTONE PARTNERSHIP.....................................  A-11
    2.1      Organization, Standing and Power............................  A-12
    2.2      Cornerstone Subsidiaries....................................  A-12
    2.3      Capital Structure...........................................  A-13
    2.4      Other Interests.............................................  A-14
    2.5      Authority; Noncontravention; Consents.......................  A-14
    2.6      SEC Documents; Financial Statements; Undisclosed
             Liabilities.................................................  A-16
    2.7      Absence of Certain Changes or Events........................  A-16
    2.8      Litigation..................................................  A-17
    2.9      Properties..................................................  A-17
   2.10      Environmental Matters.......................................  A-19
   2.11      Related Party Transactions..................................  A-20
   2.12      Employee Benefits...........................................  A-20
   2.13      Employee Policies...........................................  A-21
   2.14      Taxes.......................................................  A-22
   2.15      No Payments to Employees, Officers or Directors.............  A-23
   2.16      Broker; Schedule of Fees and Expenses.......................  A-23
   2.17      Compliance with Laws........................................  A-23
   2.18      Contracts; Debt Instruments.................................  A-23
   2.19      Opinion of Financial Advisor................................  A-25
   2.20      State Takeover Statutes.....................................  A-25
   2.21      Investment Company Act of 1940..............................  A-25
   2.22      Definition of Knowledge of Cornerstone......................  A-25
   2.23      Required Stockholder Approvals and Partner Approvals........  A-25
ARTICLE 3    REPRESENTATIONS AND WARRANTIES OF EOP AND EOP PARTNERSHIP...  A-26
    3.1      Organization, Standing and Power of EOP.....................  A-26
    3.2      EOP Subsidiaries............................................  A-26
    3.3      Capital Structure...........................................  A-27
    3.4      Other Interests.............................................  A-28
</TABLE>

                                        i
<PAGE>   230

<TABLE>
<CAPTION>
                                                                           PAGE
                                                                           ----
<C>          <S>                                                           <C>
    3.5      Authority; Noncontravention; Consents.......................  A-28
    3.6      SEC Documents; Financial Statements; Undisclosed
             Liabilities.................................................  A-29
    3.7      Absence of Certain Changes or Events........................  A-29
    3.8      Litigation..................................................  A-30
    3.9      Properties..................................................  A-30
   3.10      Environmental Matters.......................................  A-31
   3.11      Taxes.......................................................  A-32
   3.12      Brokers; Schedule of Fees and Expenses......................  A-33
   3.13      Compliance with Laws........................................  A-33
   3.14      Contracts; Debt Instruments.................................  A-33
   3.15      Opinion of Financial Advisor................................  A-33
   3.16      State Takeover Statutes.....................................  A-33
   3.17      Investment Company Act of 1940..............................  A-33
   3.18      Definition of Knowledge of EOP..............................  A-33
   3.19      Required Shareholder Approvals and Partner Approvals........  A-33
ARTICLE 4    COVENANTS...................................................  A-34
    4.1      Conduct of Cornerstone's and Cornerstone Partnership's
             Business Pending Merger.....................................  A-34
    4.2      Conduct of EOP's and EOP Partnership's Business Pending
             Merger......................................................  A-36
    4.3      No Solicitation.............................................  A-38
    4.4      Affiliates..................................................  A-39
    4.5      Other Actions...............................................  A-40
ARTICLE 5    ADDITIONAL COVENANTS........................................  A-40
    5.1      Preparation of the Form S-4 and the Proxy Statement;
             Cornerstone Stockholders Meeting, Cornerstone Unitholders
             Consent Solicitation and EOP Shareholders Meeting...........  A-40
    5.2      Access to Information; Confidentiality......................  A-42
    5.3      Commercially Reasonable Efforts; Notification...............  A-42
    5.4      Tax Matters.................................................  A-43
    5.5      Public Announcements........................................  A-44
    5.6      Listing.....................................................  A-45
    5.7      Transfer and Gains Taxes....................................  A-45
    5.8      Benefit Plans and Other Employee Arrangements...............  A-45
    5.9      Indemnification.............................................  A-46
   5.10      Declaration of Dividends and Distributions..................  A-48
   5.11      Transfer of Non-Controlled Subsidiary Voting Shares.........  A-49
   5.12      Notices.....................................................  A-49
   5.13      Resignations................................................  A-49
   5.14      Assumption of Existing Tax Protection Agreements............  A-49
   5.15      EOP Partnership Agreement...................................  A-49
   5.16      Registration Rights Agreements..............................  A-49
   5.17      Cornerstone Convertible Promissory Note.....................  A-49
ARTICLE 6    CONDITIONS..................................................  A-50
    6.1      Conditions to Each Party's Obligation to Effect the
             Mergers.....................................................  A-50
    6.2      Conditions to Obligations of EOP and EOP Partnership........  A-50
    6.3      Conditions to Obligations of Cornerstone and Cornerstone
             Partnership.................................................  A-51
ARTICLE 7    TERMINATION, AMENDMENT AND WAIVER...........................  A-53
    7.1      Termination.................................................  A-53
    7.2      Certain Fees and Expenses...................................  A-54
    7.3      Effect of Termination.......................................  A-55
    7.4      Amendment...................................................  A-55
</TABLE>

                                       ii
<PAGE>   231

<TABLE>
<CAPTION>
                                                                           PAGE
                                                                           ----
<C>          <S>                                                           <C>
    7.5      Extension; Waiver...........................................  A-55
ARTICLE 8    GENERAL PROVISIONS..........................................  A-56
    8.1      Nonsurvival of Representations and Warranties...............  A-56
    8.2      Notices.....................................................  A-56
    8.3      Interpretation..............................................  A-57
    8.4      Counterparts................................................  A-57
    8.5      Entire Agreement; No Third-Party Beneficiaries..............  A-57
    8.6      Governing Law...............................................  A-57
    8.7      Assignment..................................................  A-57
    8.8      Enforcement.................................................  A-57
    8.9      Severability................................................  A-57
   8.10      Exculpation.................................................  A-58
   8.11      Joint and Several Obligations...............................  A-58
</TABLE>

                                    EXHIBITS

Exhibit "A" -- Form of Certificate of Merger

Exhibit "B" -- Form of Maryland Articles of Merger

Exhibit "C" -- Form of Nevada Articles of Merger

Exhibit "D" -- Form of Proposed EOP Charter Amendment Relating to Certain Voting
               Requirements

Exhibit "E" -- Form of Proposed EOP Charter Amendment Relating to Domestically
               Controlled REIT Status

                                       iii
<PAGE>   232

                             INDEX OF DEFINED TERMS

<TABLE>
<S>                                                           <C>
AICPA Statement.............................................  5.1(b)
Acquisition Proposal........................................  4.3(a)(i)
Affiliate...................................................  2.11
Agreement...................................................  Preamble
Base Amount.................................................  7.2
BeaMet......................................................  3.11(b)
Break-Up Fee................................................  7.2
Break-Up Fee Tax Opinion....................................  7.2
Break-Up Expenses...........................................  7.2
Cash Election...............................................  1.11(a)
Cash Election Shares........................................  1.12(a)
Cash Fraction...............................................  1.12(b)
CERCLA......................................................  2.10(a)
Certificate of Merger.......................................  C
Certificate.................................................  1.10(b)(iv)
Closing.....................................................  1.3
Closing Date................................................  1.3
Cornerstone.................................................  Preamble
Cornerstone Acquisition Agreement...........................  7.2
Cornerstone Articles........................................  2.1
Cornerstone Bylaws..........................................  2.1
Cornerstone Common Stock....................................  1.10(b)(i)
Cornerstone Convertible Promissory Note.....................  2.3(c)
Cornerstone Disclosure Letter...............................  Art. 2
Cornerstone Financial Statement Date........................  2.7
Cornerstone Material Adverse Change.........................  2.7
Cornerstone Material Adverse Effect.........................  2.1
Cornerstone Non-controlled Subsidiary.......................  J
Cornerstone OP Unit.........................................  1.1(a)
Cornerstone Other Interests.................................  2.4
Cornerstone Partner Approvals...............................  1.13
Cornerstone Partnership.....................................  Preamble
Cornerstone Partnership Agreement...........................  1.5
Cornerstone Preferred OP Unit...............................  1.10(a)(ii)
Cornerstone Properties......................................  2.9(a)
Cornerstone Rent Roll.......................................  2.9(e)
Cornerstone SEC Documents...................................  2.6
Cornerstone 7% Preferred Stock..............................  1.10(b)(iii)
Cornerstone Stockholder Approvals...........................  2.5(a)
Cornerstone Stockholders Meeting............................  5.1(d)
Cornerstone Space Lease.....................................  2.9(e)
Cornerstone Stock Options...................................  2.3(b)
Cornerstone Stock Rights....................................  2.3(b)
Cornerstone Subsidiaries....................................  2.2(a)
Cornerstone Voting Agreement................................  K
Code........................................................  F
Commitment..................................................  4.1(i)
Common Stock Exchange Ratio.................................  1.10(b)(ii)
Confidentiality Agreement...................................  2.18(k)
Controlled Group Member.....................................  2.12
Department..................................................  1.4
</TABLE>

                                       iv
<PAGE>   233
<TABLE>
<S>                                                           <C>
DRULPA......................................................  1.1(b)
Effective Time..............................................  1.4
Electing Cornerstone OP Units...............................  1.11
Election....................................................  1.11(a)
Election Date...............................................  1.11(d)
Employee Plan...............................................  2.12
Encumbrances................................................  2.9(a)
Environmental Law...........................................  2.10(a)
Environmental Permits.......................................  2.10(b)(iv)
EOP.........................................................  Preamble
EOP Bylaws..................................................  1.6
EOP Common Share............................................  1.10(b)(ii)
EOP Counter Proposal........................................  4.3(c)
EOP Declaration of Trust....................................  1.6
EOP Disclosure Letter.......................................  Art. 3
EOP Financial Statement Date................................  3.7
EOP Material Adverse Change.................................  3.7
EOP Material Adverse Effect.................................  3.1
EOP NCS Sub.................................................  J
EOP Options.................................................  3.3(b)
EOP OP Unit.................................................  1.10(a)(i)
EOP Other Interests.........................................  3.4
EOP Partner Approvals.......................................  1.13
EOP Partnership.............................................  Preamble
EOP Partnership Agreement...................................  1.5
EOP Preferred OP Unit.......................................  1.10(a)(ii)
EOP Preferred Units.........................................  3.3(e)
EOP Preferred Shares........................................  3.3(a)
EOP Properties..............................................  3.9(a)
EOP Rent Roll...............................................  3.9(g)
EOP SEC Documents...........................................  3.6
EOP Shareholder Approvals...................................  3.5(a)
EOP Shareholders Meeting....................................  5.1(c)
EOP Space Lease.............................................  3.9(g)
EOP Subsidiaries............................................  3.1
ERISA.......................................................  2.12
Exchange Act................................................  2.6
Exchange Agent..............................................  1.15(a)
Exchange Fund...............................................  1.15(b)
Exercise....................................................  1.1(a)(i)
Final Company Dividend......................................  1.15(d)(i)
Form of Election............................................  1.11(b)
Form S-4....................................................  5.1(a)
Former Cornerstone Properties...............................  2.10(b)(ii)
GAAP........................................................  2.6
Governmental Entity.........................................  2.5(c)
Hazardous Materials.........................................  2.10
HSR Act.....................................................  2.5(c)
Indebtedness................................................  2.18(b)
Indemnification Parties.....................................  5.9(b)
Indemnified Parties.........................................  5.9(a)
Indemnifying Parties........................................  5.9(a)
Joint Proxy Statement.......................................  5.1(a)
</TABLE>

                                        v
<PAGE>   234
<TABLE>
<S>                                                           <C>
Knowledge of Cornerstone....................................  2.22
Knowledge of EOP............................................  3.18
Laws........................................................  2.5(c)
Liens.......................................................  2.2(b)
Maryland Articles of Merger.................................  D
Maximum Amount..............................................  7.2
Merger......................................................  A
Mergers.....................................................  B
Merger Consideration........................................  1.10(b)
Nevada Articles of Merger...................................  E
Non-Electing Shares.........................................  1.12(e)
NRS.........................................................  1.2
NYSE........................................................  1.15(g)(ii)
Partner Approvals...........................................  1.13
Partnership Merger..........................................  B
Payor.......................................................  7.2
Pension Plan................................................  2.12
Permitted Title Exceptions..................................  2.9(a)
Person......................................................  2.2(a)
PGGM........................................................  6.3(h)
Prohibited Transaction......................................  2.12(c)
Property Restrictions.......................................  2.9(a)
Proposed EOP Charter Amendment Relating to Domestically
  Controlled REIT Status....................................  4.2(h)
Proposed EOP Charter Amendment Relating to Certain Voting
  Requirements..............................................  4.2(h)
Proposed EOP Charter Amendments.............................  4.2(h)
Qualifying Income...........................................  7.2
Recipient...................................................  7.2
REIT........................................................  2.14(b)
REIT Requirements...........................................  7.2
Release.....................................................  2.10(a)
Rule 145 Affiliates.........................................  4.4
SEC.........................................................  2.5(c)
Section 704(c) values.......................................  5.4(b)
Securities Act..............................................  2.3(g)
Share Election..............................................  1.11(a)
Shareholder Approvals.......................................  3.5(a)
Stock Election Shares.......................................  1.12(a)
Stock Fraction..............................................  1.12(c)
Stock Purchase Agreement....................................  J
Subsidiary..................................................  2.2(a)
Substituted Option..........................................  5.8(c)
Superior Acquisition Proposal...............................  4.3(d)
Surviving Trust.............................................  1.2
Takeover Statute............................................  2.20
Taxes.......................................................  2.14(a)
Tax Protection Agreements...................................  2.18(j)
Title 3.....................................................  1.2
Title 8.....................................................  1.2
Transfer and Gains Taxes....................................  5.7
Welfare Plan................................................  2.12
1940 Act....................................................  2.21
</TABLE>

                                       vi
<PAGE>   235

                          AGREEMENT AND PLAN OF MERGER

     THIS AGREEMENT AND PLAN OF MERGER (this "Agreement"), dated as of February
11, 2000, by and among EQUITY OFFICE PROPERTIES TRUST, a Maryland real estate
investment trust ("EOP"), EOP OPERATING LIMITED PARTNERSHIP, a Delaware limited
partnership ("EOP Partnership"), CORNERSTONE PROPERTIES INC., a Nevada
corporation ("Cornerstone"), and CORNERSTONE PROPERTIES LIMITED PARTNERSHIP, a
Delaware limited partnership ("Cornerstone Partnership").

                                   RECITALS:

     A. The Board of Trustees of EOP and the Board of Directors of Cornerstone
deem it advisable and in the best interests of their respective shareholders and
stockholders, upon the terms and subject to the conditions contained herein,
that Cornerstone shall merge with and into EOP (the "Merger").

     B. EOP, as the managing general partner of EOP Partnership, and
Cornerstone, as the sole general partner of Cornerstone Partnership, deem it
advisable and in the best interests of their respective limited partners,
subject to the conditions and other provisions contained herein, that,
immediately prior to the Merger, Cornerstone Partnership shall merge with and
into EOP Partnership, with the holders of partnership interests in Cornerstone
Partnership at the time of the Partnership Merger receiving in any event units
of limited partnership interest in EOP Partnership, as set forth herein (the
"Partnership Merger" and, together with the Merger, the "Mergers"). As an
alternative to receiving units of limited partnership interest in EOP
Partnership in connection with the Partnership Merger, limited partners in
Cornerstone Partnership (other than Cornerstone) shall have the right to elect,
effective immediately prior to the Partnership Merger, to exercise their
redemption right under the Cornerstone Partnership Agreement (as defined
herein), regardless of whether or not they would otherwise be entitled to
exercise that redemption right under the Cornerstone Partnership Agreement, and
Cornerstone shall issue shares of Cornerstone Common Stock (as defined herein)
in satisfaction of that right, thereby allowing former limited partners in
Cornerstone Partnership (other than Cornerstone) to participate in the Merger as
holders of Cornerstone Common Stock.

     C. Upon the terms and subject to the conditions set forth herein,
immediately prior to the Merger, EOP Partnership and Cornerstone Partnership
shall execute a Certificate of Merger (the "Certificate of Merger") in
substantially the form attached hereto as Exhibit A and shall file such
Certificate of Merger in accordance with Delaware law to effectuate the
Partnership Merger.

     D. Upon the terms and subject to the conditions set forth herein,
immediately following the effectiveness of the Partnership Merger, EOP and
Cornerstone shall execute Articles of Merger (the "Maryland Articles of Merger")
in substantially the form attached hereto as Exhibit B and shall file such
Maryland Articles of Merger in accordance with Maryland law to effectuate the
Merger.

     E. Upon the terms and subject to the conditions set forth herein,
immediately following the effectiveness of the Partnership Merger, EOP and
Cornerstone shall execute Articles of Merger (the "Nevada Articles of Merger")
in substantially the form attached hereto as Exhibit C and concurrently with the
filing of the Maryland Articles of Merger, shall file such Nevada Articles of
Merger in accordance with Nevada law to effectuate the Merger.

     F. For federal income tax purposes, it is intended that the Merger shall
qualify as a reorganization under Section 368(a) of the Internal Revenue Code of
1986, as amended (the "Code"), and that this Agreement shall constitute a plan
of reorganization under Section 368(a) of the Code.

     G. For federal income tax purposes, it is intended that the Partnership
Merger, regardless of form, be treated as a contribution by Cornerstone
Partnership of all of its assets to EOP Partnership in exchange for partnership
interests in EOP Partnership, as provided for herein, under Section 721 of the
Code, and a distribution of such partnership interests by Cornerstone
Partnership to its partners under Section 731 of the Code.
                                       A-1
<PAGE>   236

     H. EOP and Cornerstone have each received a fairness opinion relating to
the transactions contemplated hereby as more fully described herein.

     I. EOP, EOP Partnership, Cornerstone and Cornerstone Partnership desire to
make certain representations, warranties and agreements in connection with the
Mergers.

     J. Concurrently with the execution of this Agreement and as an inducement
to EOP and EOP Partnership to enter into this Agreement, William Wilson III and
John S. Moody, as the owners of 99% of the voting capital stock of WCP Services,
Inc., a Delaware corporation (the "Cornerstone Non-controlled Subsidiary"), have
entered into a Stock Purchase Agreement, dated as of the date hereof, relating
to the voting capital stock of the Cornerstone Non-controlled Subsidiary (the
"Stock Purchase Agreement"), providing for the sale of all of the outstanding
voting capital stock of the Cornerstone Non-controlled Subsidiary to EOP Office
Properties Management Corporation ("EOP NCS Sub") or its assigns.

     K. As an inducement to EOP to enter into this Agreement, (a) Stichting
Pensioenfonds voor de Gezondheid, Geestelijke en Maatschappelijke Belangen, a
stichting formed according to the laws of the Kingdom of The Netherlands, each
of the directors and certain executive officers of Cornerstone (and the spouses
of certain of the foregoing) and certain entities controlled by any of the
foregoing have entered into a voting agreement (each, a "Cornerstone Voting
Agreement"), pursuant to which such person or entity has agreed, among other
things, to vote his or its shares of Cornerstone Common Stock and Cornerstone OP
Units (as defined herein) to approve this Agreement, the respective Mergers and
any other matter which requires his or its vote in connection with the
transactions contemplated by this Agreement and (b) the holders of the
outstanding Cornerstone 7% Preferred Stock (as defined herein) have entered into
a stock option agreement, pursuant to which such holders have granted
Cornerstone and EOP an option to acquire, among other things, all of their
Cornerstone 7% Preferred Stock at any time prior to the Effective Time (as
defined herein) of the Merger at a per share purchase price of $18.00, together
with accrued and unpaid dividends to the Effective Time, in cash (subject to
adjustment).

     L. As an inducement to Cornerstone to enter into this Agreement, each of
the trustees and certain executive officers of EOP (and the spouses of certain
of the foregoing) and certain entities controlled by any of the foregoing have
entered into a voting agreement pursuant to which such person or entity has
agreed, among other things, to vote his or its EOP Common Shares (as defined
herein) to approve this Agreement, the Merger and any other matter which
requires his or its vote in connection with the transactions contemplated by
this Agreement.

     NOW, THEREFORE, in consideration of the premises and the mutual
representations, warranties, covenants and agreements contained herein, the
parties hereto hereby agree as follows:

                                   ARTICLE 1

                                  THE MERGERS

     1.1 Election by Limited Partners in Cornerstone Partnership to Exercise the
Redemption Right; The Partnership Merger.

     (a) Notwithstanding any limitation or restriction contained in the
Cornerstone Partnership Agreement with respect to the ability of a Limited
Partner (as defined in the Cornerstone Partnership Agreement) to exercise the
Redemption Right (as defined in the Cornerstone Partnership Agreement)
(including, without limitation, any limitation or restriction contained in
Section 8.6A of the Cornerstone Partnership Agreement), every Limited Partner
shall have the right to exercise the Redemption Right by submitting to
Cornerstone Partnership (with a copy to Cornerstone) during the period between
the mailing date of the Joint Proxy Statement (as defined herein) for the
Cornerstone Stockholders Meeting (as defined herein) and 5:00 p.m., Eastern
time, on the second business day prior to the date of the Cornerstone
Stockholders Meeting a Notice of Redemption (as defined in the Cornerstone
Partnership Agreement) specifying the number of Class A Partnership Common Units
(as defined in the Cornerstone Partnership Agreement) of Cornerstone Partnership
(the "Cornerstone OP Units") which such Limited Partner desires to have

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redeemed pursuant to Section 8.6A of the Cornerstone Partnership Agreement (as
modified by this Section 1.1(a)), which Notice of Redemption shall be
conditioned upon the closing of the Partnership Merger and can be conditional as
set forth in clause (v) below; provided, that,

          (i) with respect to each Notice of Redemption (a copy of the form of
     which shall accompany or form a part of the Form of Election (as defined
     herein)) properly submitted by a Limited Partner in accordance with this
     Section 1.1(a) (an "Exercise"), Cornerstone shall elect in accordance with
     Section 8.6B of the Cornerstone Partnership Agreement to purchase the
     Cornerstone OP Units relating to such Exercise by paying the REIT Shares
     Amount (as defined in the Cornerstone Partnership Agreement) and not the
     Cash Amount (as defined in the Cornerstone Partnership Agreement);

          (ii) notwithstanding the provisions of Section 8.6B of the Cornerstone
     Partnership Agreement, Cornerstone shall not be required to notify the
     Redeeming Partner (as defined in the Cornerstone Partnership Agreement) of
     Cornerstone's election to purchase the Cornerstone OP Units as described in
     the foregoing clause (i);

          (iii) the Specified Redemption Date (as defined in the Cornerstone
     Partnership Agreement) shall be the Closing Date (as defined herein) at a
     time prior to the consummation of the Partnership Merger;

          (iv) each Redeeming Partner shall be treated as an owner of the shares
     of Cornerstone Common Stock issued pursuant to this Agreement at the
     Effective Time (as defined herein) of the Merger and shall have the same
     right as each of the other holders of shares of Cornerstone Common Stock to
     make an Election (as defined herein) pursuant to Section 1.11 as to the
     form of consideration to be received in the Merger with respect to such
     shares of Cornerstone Common Stock; and

          (v) a Redeeming Partner shall have the option, in its discretion, to
     make its Notice of Redemption conditional upon part or all of the shares of
     Cornerstone Common Stock that would be issued pursuant thereto being
     converted solely into the right to receive cash in the Merger pursuant to
     Section 1.10(b)(i) and the procedures set forth in Sections 1.11 and 1.12,
     in which event the Notice of Redemption shall not be effective with respect
     to any Cornerstone OP Units for which the shares of Cornerstone Common
     Stock that would be received therefor would not be converted entirely into
     the right to receive cash in the Merger (and any Cornerstone OP Units not
     redeemed as a result thereof would be converted into EOP OP Units (as
     defined herein) in the Partnership Merger as set forth in Section
     1.10(a)(i)).

     (b) Upon the terms and subject to the conditions of this Agreement, and in
accordance with Title 6, Chapter 17 of the Delaware Code Annotated, as amended
(the "DRULPA"), immediately prior to the consummation of the Merger, Cornerstone
Partnership shall be merged with and into EOP Partnership, with EOP Partnership
as the surviving limited partnership or limited liability company, and with the
holders of partnership interests in Cornerstone Partnership receiving in any
event units of partnership interest in EOP Partnership, as set forth in Section
1.10.

     1.2 The Merger. Upon the terms and subject to the conditions set forth in
this Agreement, and in accordance with Title 3 of the Corporations and
Associations Article of the Annotated Code of Maryland, as amended ("Title 3"),
Title 8 of the Corporations and Associations Article of the Annotated Code of
Maryland, as amended ("Title 8"), and Chapter 92A of Title 7 of the Nevada
Revised Statutes Annotated (the "NRS"), immediately following the effectiveness
of the Partnership Merger, Cornerstone shall be merged with and into EOP, with
EOP surviving as a real estate investment trust (the "Surviving Trust").

     1.3 Closing. The closing of the Mergers (the "Closing") will take place
commencing at 9:00 a.m., local time, on the date to be specified by the parties,
which (subject to satisfaction or waiver of the conditions set forth in Article
6) shall be no later than the third business day after satisfaction or waiver of
the conditions set forth in Section 6.1(a) (the "Closing Date"), at the offices
of Hogan & Hartson L.L.P., 555 Thirteenth Street, N.W., Washington, D.C. 20004,
unless another date or place is agreed to in writing by the parties.
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     1.4 Effective Time. As soon as practicable following the satisfaction or
waiver of the conditions set forth in Article 6, (i) EOP Partnership and
Cornerstone Partnership shall execute and file the Certificate of Merger,
executed in accordance with the DRULPA, with the Office of the Secretary of
State of the State of Delaware, and (ii) EOP and Cornerstone shall then execute
and file the Maryland Articles of Merger, executed in accordance with Title 3
and Title 8, with the State Department of Assessments and Taxation of Maryland
(the "Department"), and the Nevada Articles of Merger, executed in accordance
with Title 7 of the NRS with the Secretary of State of the State of Nevada, and
shall make all other filings and recordings required, with respect to the
Partnership Merger, under the DRULPA or, with respect to the Merger, under Title
3, Title 8 and the NRS. The Mergers shall become effective (each an "Effective
Time" and collectively the "Effective Times") at such times as EOP and
Cornerstone shall agree should be specified in the Certificate of Merger, the
Maryland Articles of Merger and the Nevada Articles of Merger (not to exceed
thirty (30) days after the Maryland Articles of Merger are accepted for record
by the Department). Unless otherwise agreed, the parties shall cause the
Effective Times to occur on the Closing Date, with not less than one hour
between the Effective Time of the Partnership Merger and the Effective Time of
the Merger.

     1.5 Effect of Partnership Merger on Agreements of Limited Partnership. The
Agreement of Limited Partnership, as amended, of EOP Partnership, as in effect
immediately prior to the Effective Time of the Partnership Merger (the "EOP
Partnership Agreement"), shall continue in full force and effect after the
Partnership Merger until further amended in accordance with applicable Delaware
law. The Agreement of Limited Partnership, as amended, of Cornerstone
Partnership, as in effect immediately prior to the Effective Time of the
Partnership Merger (the "Cornerstone Partnership Agreement") shall terminate at
the Effective Time of Partnership Merger.

     1.6 Effect of Merger on Declaration of Trust and Bylaws. The Articles of
Amendment and Restatement of Declaration of Trust, as amended, of EOP (the "EOP
Declaration of Trust") and the Bylaws of EOP (the "EOP Bylaws"), as in effect
immediately prior to the Effective Time of the Merger and, if approved by the
EOP shareholders, as amended by the Proposed EOP Charter Amendment Relating to
Domestically Controlled REIT Status (as defined herein) and the Proposed EOP
Charter Amendment Relating to Certain Voting Requirements (as defined herein),
shall continue in full force and effect after the Merger and, until further
amended in accordance with applicable Maryland law and, if approved by the EOP
shareholders, as amended by the Proposed EOP Charter Amendment Relating to
Domestically Controlled REIT Status (as defined herein) and the Proposed EOP
Charter Amendment Relating to Certain Voting Requirements (as defined herein).

     1.7 Trustees of EOP. The trustees of EOP following the Merger shall consist
of the trustees of EOP immediately prior to the Effective Time of the Merger,
who shall continue to serve for the balance of their unexpired terms or their
earlier death, resignation or removal, together with John S. Moody, William
Wilson III and Jan van der Vlist, each of whom shall, no later than the third
business day after the Effective Time of the Merger, become a trustee with terms
expiring in 2002, 2003 and 2003, respectively. Upon the expiration of the terms
of Mr. van der Vlist in 2003 and 2006, so long as PGGM and its Affiliates
continue to own in the aggregate 21,000,000 (as adjusted for stock splits,
reverse stock splits, stock dividends and similar actions) or more of the issued
and outstanding EOP Common Shares at all times up to the meeting of shareholders
at which trustees are being elected in such years, EOP shall take all action
necessary to nominate Mr. van der Vlist for re-election as a trustee of EOP for
an additional three-year term at any special or annual meeting of shareholders
at which trustees are being elected (or in connection with a written consent in
lieu of a meeting pursuant to which trustees are proposed to be elected). In the
event that Mr. Van der Vlist shall fail to stand for re-election as aforesaid
for any reason in either 2003 or 2006 or in the event of his earlier death or
resignation, and so long as PGGM and its Affiliates continue to own in the
aggregate 21,000,000 (as adjusted for stock splits, reverse stock splits, stock
dividends and similar actions) or more of the issued and outstanding EOP Common
Shares at such time, EOP shall take all action necessary to nominate a
replacement designated by PGGM, which replacement shall be subject to the
approval of EOP if such replacement is not an officer, director or employee of
PGGM, for election or re-election as a trustee of EOP for an additional
three-year term at

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<PAGE>   239

any special or annual meeting of shareholders at which trustees are being
elected (or in connection with a written consent in lieu of a meeting pursuant
to which trustees are proposed to be elected) or, in the case of a vacancy, at a
meeting of the Board of Trustees called for such purpose. Except as expressly
provided above in this Section 1.7, following their election as trustees, such
persons shall serve for their designated terms, subject to their earlier death,
resignation or removal.

     1.8 Effect on Shares. The effect of the Merger on the shares of capital
stock of Cornerstone shall be as provided in the Articles of Merger and in
Section 1.10 hereof. The Merger shall not change the shares of beneficial
interest of EOP outstanding immediately prior to the Merger.

     1.9 Effect on Partnership Interests. The effect of the Partnership Merger
on the partnership interests of Cornerstone Partnership shall be as provided in
the Certificate of Merger and in Section 1.10 hereof. The Partnership Merger
shall not change the partnership interests of EOP Partnership outstanding
immediately prior to the Merger.

     1.10 Exchange Ratios and Other Merger Consideration.

     (a) (i) The exchange ratio relating to the Partnership Merger shall be
0.7009 of a Class A Unit (as defined in the EOP Partnership Agreement) of EOP
Partnership ("EOP OP Unit"), for each Cornerstone OP Unit outstanding
immediately prior to the Effective Time of the Partnership Merger. The holders
of the EOP OP Units issued in the Partnership Merger (other than Cornerstone and
Subsidiaries (as defined herein) of Cornerstone) shall be entitled to redeem
such EOP OP Units immediately following the consummation of the Partnership
Merger (and thereafter) pursuant to the terms of the EOP Partnership Agreement,
except that for purposes of the exchange provisions thereof such EOP OP Units
shall be deemed to have been issued as of the date the related Cornerstone OP
Units were issued by Cornerstone Partnership (or if earlier, one year prior to
the Effective Time of the Partnership Merger), and shall be entitled to the same
rights and privileges as the holders of EOP OP Units outstanding on the date
hereof.

     (ii) The exchange ratio relating to the Partnership Merger shall be one
Class D Preferred Unit (as defined in the EOP Partnership Agreement), designated
a Class D 7.0% Cumulative Convertible Preferred Unit, of EOP Partnership ("EOP
Preferred OP Units"), for each Class A Partnership Preferred Unit (as defined in
the Cornerstone Partnership Agreement), designated a Class A 7% Cumulative
Convertible Preferred Unit of Cornerstone Partnership ("Cornerstone Preferred OP
Unit") outstanding immediately prior to the Effective Time of the Partnership
Merger. EOP, as the holder of the EOP Preferred OP Units issued in the
Partnership Merger, shall be entitled to the same rights and privileges as
Cornerstone, as the holder of the Cornerstone Preferred Units outstanding on the
date hereof.

     (b) The merger consideration to be paid to holders of capital stock of
Cornerstone in the Merger (collectively, the "Merger Consideration") is as
follows:

          (i) Each share of common stock with no par value of Cornerstone
     ("Cornerstone Common Stock") issued and outstanding immediately prior to
     the Effective Time of the Merger, which under the terms of Section 1.12 is
     to be converted into cash, shall be converted into the right to receive
     $18.00 in cash, without interest;

          (ii) Except as otherwise provided in Sections 1.10(b)(i) and 1.12, and
     subject to Section 1.15(g), each share of Cornerstone Common Stock issued
     and outstanding immediately prior to the Effective Time of the Merger
     (other than shares to be converted into the right to receive cash pursuant
     to Sections 1.10(b)(i) and 1.12) shall be converted into the right to
     receive 0.7009 of a validly issued, fully paid and nonassessable common
     share of beneficial interest, par value $.01 per share, of EOP (an "EOP
     Common Share") (the "Common Stock Exchange Ratio");

          (iii) Each share of 7.0% Cumulative Convertible Preferred Stock with
     no par value of Cornerstone ("Cornerstone 7% Preferred Stock") outstanding
     immediately prior to the Effective Time of the Merger shall be converted
     into the right to receive $18.00, together with accrued and unpaid
     dividends to the Effective Time of the Merger, in cash, without interest;
     and

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          (iv) All such shares of Cornerstone Common Stock, when so converted as
     provided in Section 1.10(b)(i) or (ii), and all such shares of Cornerstone
     7% Preferred Stock, when so converted as provided in Section 1.10(b)(iii),
     shall no longer be outstanding and shall automatically be cancelled and
     retired and shall cease to exist, and each holder of a certificate (a
     "Certificate") theretofore representing any such shares shall cease to have
     any rights with respect thereto, except the right to receive, upon the
     surrender of such Certificate in accordance with Section 1.15(c), as
     applicable, (A) any dividends and other distributions in accordance with
     Section 1.15(d), (B) certificates representing the EOP Common Shares into
     which such shares of Cornerstone Common Stock are converted pursuant to
     Section 1.10(c)(ii) (if any), (C) cash into which such shares of
     Cornerstone Common Stock are converted pursuant to Section 1.10(c)(i), (D)
     cash into which such shares of Cornerstone 7% Preferred Stock are converted
     pursuant to Section 1.10(b)(iii), and (E) any cash, without interest, in
     lieu of fractional EOP Common Shares to be issued or paid in consideration
     for Cornerstone Common Stock upon the surrender of such Certificate in
     accordance with Sections 1.15(c) and 1.15(g).

     1.11 Election by Holders of Cornerstone Common Stock to Receive EOP Common
Shares or Cash. Each holder of shares of Cornerstone Common Stock (including,
without limitation, Limited Partners of Cornerstone Partnership who elect to
exercise, on a conditional or unconditional basis, the Redemption Right with
respect to all or a portion of their Cornerstone OP Units held by such Limited
Partners pursuant to Section 1.1(a) (with the Cornerstone OP Units with respect
to which such Exercise is made referred to as "Electing Cornerstone OP Units"))
shall have the right to submit a Form of Election specifying the number of
shares of Cornerstone Common Stock which such holder desires to have converted
into the right to receive EOP Common Shares in the Merger pursuant to Section
1.10(a)(ii) and the number which such holder desires to have converted into the
right to receive cash pursuant to Section 1.10(a)(i) in accordance with the
following procedures:

     (a) Each holder of shares of Cornerstone Common Stock and each holder of
Electing Cornerstone OP Units may specify in a request made in accordance with
the provisions of this Section 1.11 (an "Election") (i) the number of such
shares which such holder desires to have converted into the right to receive
cash in the Merger pursuant to Section 1.10(a)(i) (a "Cash Election") and (ii)
the number of such shares which such holder desires to have converted into the
right to receive EOP Common Shares in the Merger pursuant to Section 1.10(a)(ii)
(a "Share Election").

     (b) EOP and Cornerstone shall prepare, for use by stockholders of
Cornerstone (and each holder of Electing Cornerstone OP Units) in surrendering
Certificates representing shares of Cornerstone Common Stock, a form of election
(the "Form of Election") pursuant to which each holder of Cornerstone Common
Stock and each holder of Electing Cornerstone OP Units may make Elections. The
Form of Election shall be mailed to stockholders of record of Cornerstone as of
the record date for the Cornerstone Stockholders Meeting (as defined herein) and
to each holder of Cornerstone OP Units and shall accompany the Joint Proxy
Statement (as defined herein).

     (c) Cornerstone shall use commercially reasonable efforts to make the Form
of Election available to all persons who become stockholders of record of
Cornerstone and to all Limited Partners of Cornerstone Partnership during the
period between such record date and the second business day prior to the date of
the Cornerstone Stockholders Meeting, provided that only a Limited Partner of
Cornerstone Partnership who is a holder of Electing Cornerstone OP Units may
submit a Form of Election and such Form of Election shall apply only with
respect to shares of Cornerstone Common Stock issued to such Limited Partner
prior to the Effective Time of the Partnership Merger pursuant to the Redemption
Right as set forth in Section 1.1(a).

     (d) An Election shall have been properly made only if the Exchange Agent
(as defined herein) shall have received, by 5:00 p.m., Eastern Standard Time, on
the second business day (such time on such day being referred to herein as the
"Election Date") preceding the date of the Cornerstone Stockholders Meeting, a
Form of Election properly completed and signed (and not revoked) and accompanied
(in the case of holders of shares of Cornerstone Common Stock) by the
Certificate or Certificates representing the

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shares of Cornerstone Common Stock to which such Form of Election relates, duly
endorsed in blank or otherwise in form acceptable for transfer on the books of
Cornerstone (or by an appropriate guarantee of delivery of such Certificate or
Certificates as set forth in such Form of Election from a member of any
registered national securities exchange or of the National Association of
Securities Dealers, Inc. or a commercial bank or trust company having an office
or correspondent in the United States, provided such Certificate or Certificates
are in fact delivered by the time set forth in such guarantee of delivery).

     (e) Any holder of record of shares of Cornerstone Common Stock (and any
holder of Electing Cornerstone OP Units) may at any time prior to the Election
Date change such holder's Election by written notice received by the Exchange
Agent at or prior to the Election Date accompanied by a properly completed Form
of Election. EOP and Cornerstone shall have the right in their sole discretion
and by mutual agreement to permit changes in Elections after the Election Date.

     (f) Any holder of record of shares of Cornerstone Common Stock (and any
holder of Electing Cornerstone OP Units) may at any time prior to the Election
Date revoke such holder's Election by written notice received by the Exchange
Agent at or prior to the Election Date or by withdrawal prior to the Election
Date of such holder's Certificates previously deposited with the Exchange Agent.
Any revocation of an Election may be withdrawn by notice of such withdrawal
delivered at or prior to the Election Date. Any such holder who shall have
deposited Certificates with the Exchange Agent shall have the right to withdraw
such Certificates by written notice received by the Exchange Agent and thereby
revoke such holder's Election as of the Election Date at any time after the
expiration of the period of 60 days following the Election Date if the Merger
shall not have been consummated prior thereto. EOP shall obtain from the
Exchange Agent an agreement to return all Forms of Election and accompanying
Certificates to the stockholders submitting the same in the event this Agreement
shall be terminated in accordance with its terms.

     (g) EOP and Cornerstone by mutual agreement shall have the right to make
rules, not inconsistent with the terms of this Agreement, governing the validity
of Forms of Election, the manner and extent to which Elections are to be taken
into account in making the determinations prescribed by Section 1.12, the
issuance and delivery of certificates for EOP Common Shares into which shares of
Cornerstone Common Stock are converted in the Merger and the payment for shares
of Cornerstone Common Stock converted into the right to receive cash in the
Merger.

     1.12 Proration. The determination of whether shares of Cornerstone Common
Stock shall be converted in the Merger into EOP Common Shares in accordance with
the Common Stock Exchange Ratio or the right to receive $18.00 in cash shall be
made as set forth in this Section 1.12.

     (a) As is more fully set forth below, 58,551,525 shares of Cornerstone
Common Stock shall be converted in the Merger into the right to receive $18.00
per share in cash (which shares of Cornerstone Common Stock are referred to as
the "Cash Election Shares"), and all shares of Cornerstone Common Stock issued
and outstanding immediately prior to the Effective Time of the Merger in excess
of 58,551,525 shares shall be converted in the Merger into the right to receive
EOP Common Shares in accordance with the Common Stock Exchange Ratio (which
shares of Cornerstone Common Stock are referred to as the "Stock Election
Shares").

     (b) If Cash Elections are received for a number of shares of Cornerstone
Common Stock which is greater than 58,551,525 shares of Cornerstone Common
Stock, each Non-Electing Share (as defined herein) and each share of Cornerstone
Common Stock for which a Share Election has been received shall be converted in
the Merger into EOP Common Shares in accordance with the Common Stock Exchange
Ratio, and the shares of Cornerstone Common Stock for which Cash Elections have
been received shall be converted in the Merger into the right to receive cash
and EOP Common Shares in accordance with the Common Stock Exchange Ratio in the
following manner:

          each share of Cornerstone Common Stock covered by a Cash Election
     shall be converted into the right to receive (i) an amount in cash, without
     interest, equal to the product of (x) $18.00 and (y) a fraction (the "Cash
     Fraction") the numerator of which shall be 58,551,525 and the

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     denominator of which shall be the aggregate number of shares of Cornerstone
     Common Stock covered by all Cash Elections, and (ii) a number of EOP Common
     Shares equal to the product of (x) the Common Stock Exchange Ratio and (y)
     a fraction equal to one minus the Cash Fraction.

     (c) If Share Elections are received for a number of shares of Cornerstone
Common Stock which is greater than the total number of Stock Election Shares
issued and outstanding immediately prior to the Effective Time of the Merger,
each Non-Electing Share and each share of Cornerstone Common Stock for which a
Cash Election has been received shall be converted in the Merger into the right
to receive $18.00 in cash, without interest, and the shares of Cornerstone
Common Stock for which Share Elections have been received shall be converted in
the Merger into EOP Shares in accordance with the Common Stock Exchange Ratio
and the right to receive cash in the following manner:

          each share of Cornerstone Common Stock covered by a Share Election
     shall be converted into the right to receive (i) a number of EOP Common
     Shares equal to the product of (x) the Common Stock Exchange Ratio and (y)
     a fraction (the "Stock Fraction"), the numerator of which shall be a number
     equal to the total number of Stock Election Shares issued and outstanding
     immediately prior to the Effective Time of the Merger and the denominator
     of which shall be the aggregate number of shares of Cornerstone Common
     Stock covered by all Share Elections, and (ii) an amount in cash, without
     interest, equal to the product of (x) $18.00 and (y) a fraction equal to
     one minus the Stock Fraction.

     (d) If Non-Electing Shares (as defined herein) are not converted under
either Section 1.12(b) or Section 1.12(c), then each Non-Electing Share shall be
converted into the right to receive EOP Common Shares and the right to receive
cash on a proportionate basis, relative to all other Non-Electing Shares, so
that the aggregate number of shares of Cornerstone Common Stock converted into
the right to receive EOP Common Shares equals, as closely as possible, the
number of Stock Election Shares, and the aggregate number of shares of
Cornerstone Common Stock converted into the right to receive cash equals, as
closely as possible, the number of Cash Election Shares.

     (e) For purposes of this Section 1.12, outstanding shares of Cornerstone as
to which an election is not in effect at the Election Date and shares as to
which an Election has been withdrawn after the 60-day period following the
Election Date and prior to the Effective Time of the Merger shall be called
"Non-Electing Shares." If EOP and Cornerstone shall determine for any reason
that any Election was not properly made with respect to shares of Cornerstone
Common Stock, such Election shall be deemed ineffective and shares of
Cornerstone Common Stock covered by such Election shall, for purposes hereof, be
deemed to be Non-Electing Shares.

     1.13 Partner Approval. Cornerstone shall seek the requisite approval of the
partners of Cornerstone Partnership of the Merger, the withdrawal of Cornerstone
as general partner and the Partnership Merger to the extent required by the
Cornerstone Partnership Agreement to effectuate the transactions contemplated by
this Agreement (collectively, the "Cornerstone Partner Approvals"). EOP shall
seek the requisite approval of the partners of EOP Partnership of the Merger and
the Partnership Merger to the extent required by the EOP Partnership Agreement
to effectuate the transactions contemplated by this Agreement (collectively, the
"EOP Partner Approvals," and together with the Cornerstone Partner Approvals,
the "Partner Approvals").

     1.14 No Appraisal Rights. The holders of Cornerstone Common Stock,
Cornerstone OP Units, EOP Common Shares and EOP OP Units are not entitled under
applicable law to appraisal or similar rights as a result of the Mergers and, in
the case of the holders of the Cornerstone 7% Preferred Stock, such holders
irrevocably have waived all such rights.

     1.15 Exchange of Certificates; Pre-Closing Dividends; Fractional Shares.

     (a) Exchange Agent. Prior to the Effective Time, EOP shall appoint
Equiserve LLC as the exchange agent, or another bank or trust company reasonably
acceptable to Cornerstone, to act as exchange agent (the "Exchange Agent") for
the exchange of the Merger Consideration upon surrender of certificates

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representing issued and outstanding shares of Cornerstone Common Stock and
Cornerstone 7% Preferred Stock.

     (b) EOP to Provide Merger Consideration. EOP shall provide to the Exchange
Agent on or before the Effective Time of the Merger, for the benefit of the
holders of Cornerstone Common Stock and Cornerstone 7% Preferred Stock, the
Merger Consideration issuable in exchange for the issued and outstanding
Cornerstone Common Stock and Cornerstone 7% Preferred Stock pursuant to Section
1.10, together with any cash required to make payments in lieu of any fractional
shares pursuant to Section 1.15(g) (the "Exchange Fund"). The Exchange Agent
shall invest any cash included in the Exchange Fund as directed by EOP, on a
daily basis. Any interest or other income resulting from such investments shall
be paid to EOP. Cornerstone shall provide to the Exchange Agent not later than
one business day prior to the Effective Time of the Merger, for the benefit of
the holders of Cornerstone Common Stock, cash payable in respect of any
dividends required pursuant to Section 1.15(d)(i) or (ii). Such cash shall be
invested in accordance with written directions delivered by Cornerstone to the
Exchange Agent not later than one business day prior to the Effective Time of
the Merger, with any cash earned on such investments to be paid to EOP as the
successor to Cornerstone in the Merger. EOP shall use commercially reasonable
efforts to cause the Exchange Agent to mail the Merger Consideration to the
holders of Cornerstone Common Stock (including to holders of Electing
Cornerstone OP Units who made an unconditional Exercise of the Redemption Right
or who made a conditional exercise thereof and who will receive cash in the
Merger, in each case who have properly submitted a Form of Election prior to the
Election Date) and Cornerstone 7% Preferred Stock not later than five business
days after the Effective Time of the Merger.

     (c) Exchange Procedure. As soon as reasonably practicable after the
Effective Time, EOP shall use commercially reasonable efforts to cause the
Exchange Agent to mail to each holder of record of a Certificate or Certificates
which immediately prior to the Effective Time represented outstanding shares of
Cornerstone Common Stock (other than to holders of Cornerstone Common Stock who
previously surrendered with their Forms of Election their Certificates for
Cornerstone Common Stock) or Cornerstone 7% Preferred Stock Certificate whose
shares were converted into the right to receive the Merger Consideration
pursuant to Section 1.10, (i) a letter of transmittal (which shall specify that
delivery shall be effected, and risk of loss and title to the Certificates shall
pass, only upon delivery of the Certificates to the Exchange Agent and shall be
in a form and have such other provisions as EOP may reasonably specify) and (ii)
instructions for use in effecting the surrender of the Certificates in exchange
for the Merger Consideration. To the extent not previously surrendered with a
Form of Election, upon surrender of a Certificate for cancellation to the
Exchange Agent or to such other agent or agents as may be appointed by EOP,
together with such letter of transmittal, duly executed, and such other
documents as may reasonably be required by the Exchange Agent, the holder of
such Certificate shall be entitled to receive in exchange therefor the Merger
Consideration into which the shares of Cornerstone Common Stock or Cornerstone
7% Preferred Stock, as applicable, theretofore represented by such Certificate
shall have been converted pursuant to Section 1.10, together with any dividends
or other distributions to which such holder is entitled pursuant to Section
1.15(d) and cash, if any, payable in lieu of fractional shares pursuant to
Section 1.15(g), to be mailed (or made available for collection by hand if so
elected by the surrendering holder) within five business days of receipt
thereof, and the Certificate so surrendered shall forthwith be canceled. In the
event of a transfer of ownership of shares of Cornerstone Common Stock or
Cornerstone 7% Preferred Stock which is not registered in the transfer records
of Cornerstone, payment may be made to a person other than the person in whose
name the Certificate so surrendered is registered if such Certificate shall be
properly endorsed or otherwise be in proper form for transfer and the person
requesting such payment either shall pay any transfer or other taxes required by
reason of such payment being made to a person other than the registered holder
of such Certificate or establish to the satisfaction of EOP that such tax or
taxes have been paid or are not applicable. Until surrendered as contemplated by
this Section 1.15, each Certificate shall be deemed at any time after the
Effective Time to represent only the right to receive upon such surrender the
Merger Consideration, without interest, into which the shares of Cornerstone
Common Stock or Cornerstone 7% Preferred Stock heretofore represented by such
Certificate shall have been converted pursuant to Section 1.10, and any
dividends or other distributions to
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which such holder is entitled pursuant to Section 1.15(d). No interest will be
paid or will accrue on the Merger Consideration upon the surrender of any
Certificate or on any cash payable pursuant to Section 1.15(d) or Section
1.15(g). EOP or the Exchange Agent, as applicable, shall be entitled, in its
sole and absolute discretion, to deduct and withhold from the cash or EOP Common
Shares, or any combination thereof, that otherwise is payable pursuant to this
Agreement to any holder of shares of Cornerstone Common Stock or Cornerstone 7%
Preferred Stock such amounts as EOP or the Exchange Agent is required to deduct
and withhold with respect to the making of such payment under the Code or under
any provision of state, local or foreign tax law, provided that in determining
whether withholding under Section 1445 of the Code is required, EOP shall take
into account (and shall request the Exchange Agent to take into account) Section
1445(b)(6) of the Code and Treasury Regulations Section 1.1445-2(c)(2). For this
purpose, any EOP Common Shares deducted and withheld by EOP shall be valued at
the last trading price of the EOP Common Shares on the New York Stock Exchange
on the Effective Date of the Merger. To the extent that amounts are so withheld
by EOP or the Exchange Agent, such withheld amounts shall be treated for all
purposes of this Agreement as having been paid to the holder of the shares of
Cornerstone Common Stock or Cornerstone 7% Preferred Stock, as applicable, in
respect of which such deduction and withholding was made by EOP or the Exchange
Agent.

     (d) Record Dates for Final Dividends; Distributions with Respect to
Unexchanged Shares.

          (i) To the extent necessary to satisfy the requirements of Section
     857(a)(1) of the Code for the taxable year of Cornerstone ending at the
     Effective Time of the Merger (and avoid the payment of tax with respect to
     undistributed income), Cornerstone shall declare a dividend (the "Final
     Company Dividend") to holders of shares of Cornerstone Common Stock and
     Cornerstone 7% Preferred Stock, the record date for which shall be the
     close of business on the last business day prior to the Effective Time of
     the Merger, in an amount equal to the minimum dividend sufficient to permit
     Cornerstone to satisfy such requirements. If Cornerstone determines it is
     necessary to declare the Final Company Dividend, it shall notify EOP at
     least 10 days prior to the date for the Cornerstone Stockholders Meeting,
     and EOP shall declare a dividend per share to holders of shares of EOP
     Common Shares, the record date for which shall be the close of business on
     the last business day prior to the Effective Time, in an amount per EOP
     Common Share equal to the quotient obtained by dividing (x) the Final
     Company Dividend paid by Cornerstone with respect to each share of
     Cornerstone Common Stock by (y) the Common Stock Exchange Ratio. The
     dividends payable hereunder to holders of Cornerstone Common Stock and
     Cornerstone 7% Preferred Stock shall be paid on the last business day
     immediately preceding the Closing Date.

          (ii) No dividends or other distributions with respect to EOP Common
     Shares with a record date after the Effective Time shall be paid to the
     holder of any unsurrendered Certificate with respect to the shares of EOP
     Common Shares represented thereby, and no cash payment in lieu of
     fractional shares shall be paid to any such holder pursuant to Section
     1.15(g), in each case until the surrender of such Certificate in accordance
     with this Section 1.15. Subject to the effect of applicable escheat laws,
     following surrender of any such Certificate there shall be paid to the
     holder of such Certificate, without interest, (i) at the time of such
     surrender, the amount of any cash payable pursuant to Section 1.10 and/or
     in lieu of any fractional EOP Common Shares to which such holder is
     entitled pursuant to Section 1.15(g) and (ii) if such Certificate is
     exchangeable for one or more whole EOP Common Shares, (x) at the time of
     such surrender the amount of dividends or other distributions with a record
     date after the Effective Time theretofore paid with respect to such whole
     EOP Common Shares and (y) at the appropriate payment date, the amount of
     dividends or other distributions with a record date after the Effective
     Time but prior to such surrender and with a payment date subsequent to such
     surrender payable with respect to such whole EOP Common Shares.

     (e) No Further Ownership Rights in Cornerstone Common Stock and Cornerstone
7% Preferred Stock. All Merger Consideration paid upon the surrender of
Certificates in accordance with the terms of this Section 1.15 (including any
cash paid pursuant to Section 1.15(g)) shall be deemed to have been paid in full
satisfaction of all rights pertaining to the Cornerstone Common Stock and
Cornerstone 7% Preferred Stock, as applicable, theretofore represented by such
Certificates; provided, however, that
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Cornerstone shall transfer to the Exchange Agent cash sufficient to pay any
dividends or make any other distributions with a record date prior to the
Effective Time which may have been declared or made by Cornerstone on such
Cornerstone Common Stock or Cornerstone 7% Preferred Stock in accordance with
the terms of this Agreement or prior to the date of this Agreement and which
remain unpaid at the Effective Time and have not been paid prior to such
surrender, and there shall be no further registration of transfers on the stock
transfer books of Cornerstone of the Cornerstone Common Stock or Cornerstone 7%
Preferred Stock which were outstanding immediately prior to the Effective Time.
If, after the Effective Time, Certificates are presented to EOP for any reason,
they shall be canceled and exchanged as provided in this Section 1.15.

     (f) No Liability. None of Cornerstone, EOP or the Exchange Agent shall be
liable to any person in respect of any Merger Consideration or dividends
delivered to a public official pursuant to any applicable abandoned property,
escheat or similar law. Any portion of the Exchange Fund delivered to the
Exchange Agent pursuant to this Agreement that remains unclaimed for 12 months
after the Effective Time shall be redelivered by the Exchange Agent to EOP, upon
demand, and any holders of Certificates who have not theretofore complied with
Section 1.15(c) shall thereafter look only to EOP for delivery of the Merger
Consideration and any unpaid dividends, subject to applicable escheat and other
similar laws.

     (g) No Fractional Shares

          (i) No certificates or scrip representing fractional EOP Common Shares
     shall be issued upon the surrender for exchange of Certificates, and such
     fractional share interests will not entitle the owner thereof to vote, to
     receive dividends or to any other rights of a shareholder of EOP.

          (ii) No fractional EOP Common Shares shall be issued pursuant to this
     Agreement. In lieu of the issuance of any fractional EOP Common Shares
     pursuant to this Agreement, each holder of Cornerstone Common Stock upon
     surrender of a Certificate for exchange shall be paid an amount in cash
     (without interest), rounded to the nearest cent, determined by multiplying
     (i) the average closing price of one EOP Common Share on the New York Stock
     Exchange on the five trading days immediately preceding the Closing Date by
     (ii) the fractional amount of 0.7009 of an EOP Common Share which such
     holder would otherwise be entitled to receive under this Section 1.15.

     (h) Lost Certificates. If any Certificate shall have been lost, stolen or
destroyed, upon the making of an affidavit of that fact by the person claiming
such Certificate to be lost, stolen or destroyed and, if required by EOP or the
Exchange Agent, the posting by such person of a bond in such reasonable amount
as EOP or the Exchange Agent may direct (but consistent with the practices EOP
applies to its own shareholders) as indemnity against any claim that may be made
against them with respect to such Certificate, the Exchange Agent will issue in
exchange for such lost, stolen or destroyed Certificate the EOP Common Shares or
cash to which the holders thereof are entitled pursuant to Section 1.10, any
cash payable pursuant to Section 1.15(g) to which the holders thereof are
entitled and any dividends or other distributions to which the holders thereof
are entitled pursuant to Section 1.15(d).

     (i) Applicability to Partnership Merger. Except for the provisions relating
to the Exchange Agent, certificates and the exchange procedure (which shall not
be applicable), all other provisions of this Section 1.15 shall apply to
Cornerstone Partnership, EOP Partnership, the Cornerstone OP Units and the
Cornerstone OP Preferred Units with respect to the Partnership Merger.

                                   ARTICLE 2

                 REPRESENTATIONS AND WARRANTIES OF CORNERSTONE
                          AND CORNERSTONE PARTNERSHIP

     Except as set forth in the Cornerstone SEC Documents (as defined herein) or
in the letter of even date herewith signed by the President and Chief Executive
Officer or the Chief Operating Officer of

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Cornerstone and delivered to EOP prior to the execution hereof (the "Cornerstone
Disclosure Letter"), Cornerstone and Cornerstone Partnership represent and
warrant to EOP and EOP Partnership as follows:

     2.1 Organization, Standing and Power. Cornerstone has been duly organized
and is validly existing and in good standing under the laws of the State of
Nevada. Cornerstone has all requisite corporate power and authority to own,
operate, lease and encumber its properties and carry on its business as now
being conducted. The Cornerstone Restated Articles of Incorporation, as amended
(the "Cornerstone Articles") are in effect, and no dissolution, revocation or
forfeiture proceedings regarding Cornerstone have been commenced. Cornerstone is
duly qualified or licensed to do business as a foreign corporation and is in
good standing in each jurisdiction in which the nature of its business or the
ownership or leasing of its properties makes such qualification or licensing
necessary, other than in such jurisdictions where the failure to be so qualified
or licensed, individually or in the aggregate, would not have a material adverse
effect on the business, properties, assets, financial condition or results of
operations of Cornerstone, Cornerstone Partnership and the Cornerstone
Subsidiaries (as defined herein), taken as a whole (a "Cornerstone Material
Adverse Effect"). Cornerstone has delivered to EOP complete and correct copies
of the Cornerstone Articles and Cornerstone's Amended and Restated Bylaws (the
"Cornerstone Bylaws"), in each case, as amended or supplemented to the date of
this Agreement.

     2.2 Cornerstone Subsidiaries.

     (a) Schedule 2.2 to the Cornerstone Disclosure Letter sets forth (i) each
Subsidiary (as defined herein) of Cornerstone (the "Cornerstone Subsidiaries")
and the Cornerstone Non-controlled Subsidiary (which Cornerstone Non-controlled
Subsidiary constitutes the only entity in which Cornerstone owns a non-voting
equity interest and has no right to control except as set forth on Schedule 2.4
of the Cornerstone Disclosure Letter), (ii) the ownership interest therein of
Cornerstone, (iii) if not, directly or indirectly, wholly owned by Cornerstone,
the identity and ownership interest of each of the other owners of such
Cornerstone Subsidiary or Cornerstone Non-controlled Subsidiary, as applicable,
(iv) each office property and other commercial property owned by such
Cornerstone Subsidiary or Cornerstone Non-controlled Subsidiary, as applicable,
and (v) if not wholly owned by such Cornerstone Subsidiary or Cornerstone
Non-controlled Subsidiary, as applicable, the identity and ownership interest of
each of the other owners of such property. As used in this Agreement,
"Subsidiary" of any Person (as defined herein) means any corporation,
partnership, limited liability company, joint venture, trust or other legal
entity of which such Person owns (either directly or through or together with
another Subsidiary of such Person) either (i) a general partner, managing member
or other similar interest, or (ii)(A) 10% or more of the voting power of the
voting capital stock or other equity interests, or (B) 10% or more of the
outstanding voting capital stock or other voting equity interests of such
corporation, partnership, limited liability company, joint venture or other
legal entity. As used herein, "Person" means an individual, corporation,
partnership, limited liability company, joint venture, association, trust,
unincorporated organization or other entity. Schedule 2.4 of the Cornerstone
Disclosure Letter sets forth a true and complete list of the equity securities
owned by Cornerstone, directly or indirectly, in any corporation, partnership,
limited liability company, joint venture or other legal entity, excluding
Cornerstone Subsidiaries and the Cornerstone Non-controlled Subsidiary.

     (b) Except as set forth in Schedule 2.2 to the Cornerstone Disclosure
Letter, (i) all of the outstanding shares of capital stock of each Cornerstone
Subsidiary and Cornerstone Non-controlled Subsidiary that is a corporation have
been duly authorized, validly issued and are (A) fully paid and nonassessable
and not subject to preemptive rights, (B) owned by Cornerstone or by another
Cornerstone Subsidiary or Cornerstone Non-controlled Subsidiary and (C) owned
free and clear of all pledges, claims, liens, charges, encumbrances and security
interests of any kind or nature whatsoever (collectively, "Liens") and (ii) all
equity interests in each Cornerstone Subsidiary that is a partnership, joint
venture, limited liability company or trust which are owned by Cornerstone, by
another Cornerstone Subsidiary or Cornerstone Non-controlled Subsidiary or by
Cornerstone and another Cornerstone Subsidiary or Cornerstone Non-controlled
Subsidiary are owned free and clear of all Liens other than pledges, if any,
contained in organizational documents of such Cornerstone Subsidiary and given
to secure performance thereunder. Each Cornerstone Subsidiary and Cornerstone
Non-controlled Subsidiary that is a corporation
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<PAGE>   247

is duly incorporated, validly existing and in good standing under the laws of
its jurisdiction of incorporation and has the requisite corporate power and
authority to own, operate, lease and encumber its properties and carry on its
business as now being conducted, and each Cornerstone Subsidiary that is a
partnership, limited liability company or trust is duly organized, validly
existing and in good standing under the laws of its jurisdiction of organization
and has the requisite power and authority to own, operate, lease and encumber
its properties and carry on its business as now being conducted. Each
Cornerstone Subsidiary and Cornerstone Non-controlled Subsidiary is duly
qualified or licensed to do business and is in good standing in each
jurisdiction in which the nature of its business or the ownership or leasing of
its properties makes such qualification or licensing necessary, other than in
such jurisdictions where the failure to be so qualified or licensed,
individually or in the aggregate, would not reasonably be expected to have a
Cornerstone Material Adverse Effect. Complete and correct copies of the Articles
of Incorporation, Bylaws, organization documents and partnership, joint venture
and operating agreements of each Cornerstone Subsidiary and Cornerstone
Non-controlled Subsidiary, as amended to the date of this Agreement, have been
previously delivered or made available to EOP. No effective amendment has been
made to the Cornerstone Partnership Agreement since January 21, 2000.

     2.3 Capital Structure.

     (a) The authorized shares of capital stock of Cornerstone consist of
250,000,000 shares of Cornerstone Common Stock, 129,638,245 of which are issued
and 129,280,012 of which are outstanding on the date of this Agreement, and
65,000,000 shares of preferred stock with no par value, of which 3,030,303
shares of Cornerstone 7% Preferred Stock are issued and outstanding and 344,828
shares of Redeemable Preferred Stock are designated with none outstanding on the
date of this Agreement.

     (b) Set forth in Schedule 2.3(b) to the Cornerstone Disclosure Letter is a
true and complete list of the following: (i) each qualified or nonqualified
option to purchase shares of Common Stock granted under Cornerstone's 1998
Long-Term Incentive Plan or any other formal or informal arrangement
(collectively, the "Cornerstone Stock Options"); and (ii) all other warrants or
other rights to acquire Cornerstone Common Stock, all stock appreciation rights,
restricted stock, dividend equivalents, deferred compensation accounts,
performance awards, restricted stock unit awards and other awards which are
outstanding on the date of this Agreement ("Cornerstone Stock Rights"). Schedule
2.3(b) to the Cornerstone Disclosure Letter sets forth for each Cornerstone
Stock Option and Cornerstone Stock Right the name of the grantee, the date of
the grant, the number of shares of Cornerstone Common Stock subject to each
option or other award, and the exercise price per share. On the date of this
Agreement, except as set forth in this Section 2.3 or in Schedule 2.3(b) to the
Cornerstone Disclosure Letter, no shares of Cornerstone Common Stock were
outstanding or reserved for issuance.

     (c) All outstanding shares of Cornerstone Common Stock are duly authorized,
validly issued, fully paid and nonassessable and not subject to preemptive
rights. There are no bonds, debentures, notes or other indebtedness of
Cornerstone having the right to vote (or convertible into, or exchangeable for,
securities having the right to vote) on any matters on which shareholders of
Cornerstone may vote, except for the Cornerstone convertible promissory note
dated as of January 1, 1996 which does not have voting rights but is convertible
into Cornerstone Common Stock (the "Cornerstone Convertible Promissory Note").

     (d) Other than (i) as set forth in this Section 2.3 or in Schedule 2.3(b),
2.3(c), or 2.3(d) to the Cornerstone Disclosure Letter, (ii) Cornerstone OP
Units, which may be redeemed for cash or, at the option of Cornerstone,
Cornerstone Common Stock at a rate of one share of Cornerstone Common Stock for
each Cornerstone OP Unit, (iii) shares of Cornerstone Common Stock issuable upon
the conversion of Cornerstone 7% Preferred Stock, and (iv) shares of Cornerstone
Common Stock issuable pursuant to the Cornerstone Convertible Promissory Note,
as of the date of this Agreement, there are no outstanding securities, options,
warrants, calls, rights, commitments, agreements, arrangements or undertakings
of any kind to which Cornerstone or any Cornerstone Subsidiary or Cornerstone
Non-controlled Subsidiary is a party or by which such entity is bound,
obligating Cornerstone or any Cornerstone Subsidiary or Cornerstone
Non-controlled Subsidiary to issue, deliver or sell, or cause to be issued,
delivered or sold,

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additional shares of capital stock, voting securities or other ownership
interests of Cornerstone or any Cornerstone Subsidiary or Cornerstone
Non-controlled Subsidiary or obligating Cornerstone or any Cornerstone
Subsidiary or Cornerstone Non-controlled Subsidiary to issue, grant, extend or
enter into any such security, option, warrant, call, right, commitment,
agreement, arrangement or undertaking (other than to Cornerstone or a
Cornerstone Subsidiary or a Cornerstone Non-controlled Subsidiary).

     (e) As of the date of this Agreement, 148,735,829 Cornerstone OP Units are
validly issued and outstanding, fully paid and nonassessable and not subject to
preemptive rights, of which 129,638,245 are owned by Cornerstone and 3,030,303
Cornerstone Preferred OP Units are validly issued and outstanding, fully paid
and nonassessable and not subject to preemptive rights, all of which are owned
by Cornerstone. Schedule 2.3(e) to the Cornerstone Disclosure Schedule sets
forth the name of each holder of Cornerstone OP Units and the number of
Cornerstone OP Units owned by each such holder as of the date of this Agreement.
Except as provided in the Cornerstone Partnership Agreement or as set forth on
Schedule 2.3(d), Cornerstone Partnership has not issued or granted and is not a
party to any outstanding commitments of any kind relating to, or any presently
effective agreements or understandings with respect to, the issuance or sale of
interests in Cornerstone Partnership, whether issued or unissued, or securities
convertible or exchangeable into interests in Cornerstone Partnership.

     (f) Except for the distribution of $0.31 per share of Cornerstone Common
Stock and per Cornerstone OP Unit declared on January 20, 2000, and payable on
February 29, 2000, to holders of record on January 31, 2000, of shares of
Cornerstone Common Stock and Cornerstone OP Units, all dividends on Cornerstone
Common Stock and Cornerstone 7% Preferred Stock and all distributions on
Cornerstone OP Units, which have been declared prior to the date of this
Agreement, have been paid in full.

     (g) Set forth on Schedule 2.3(g) to the Cornerstone Disclosure Letter is a
list of each registration rights agreement or other agreement between
Cornerstone and/or Cornerstone Partnership, on the one hand, and one or more
other parties, on the other hand, which sets forth the rights of any such other
party or parties to cause the registration of any securities of Cornerstone
and/or Cornerstone Partnership pursuant to the Securities Act of 1933, as
amended (the "Securities Act").

     2.4 Other Interests. Except for interests in the Cornerstone Subsidiaries,
the Cornerstone Non-controlled Subsidiary and certain other entities as set
forth in Schedule 2.4 to the Cornerstone Disclosure Letter (the "Cornerstone
Other Interests"), none of Cornerstone, Cornerstone Partnership, any Cornerstone
Subsidiary or the Cornerstone Non-controlled Subsidiary owns directly or
indirectly any interest or investment (whether equity or debt) in any
corporation, partnership, joint venture, business, trust, limited liability
company or other entity (other than investments in short-term investment
securities). With respect to the Cornerstone Other Interests, Cornerstone
Partnership owns such interests free and clear of all Liens other than pledges,
if any, contained in organizational documents of such Cornerstone Other
Interests and given to secure performance thereunder. None of Cornerstone,
Cornerstone Partnership, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary is in material breach of any provision of any
agreement, document or contract which is of a material nature governing its
rights in or to the Cornerstone Other Interests, all of which agreements,
documents and contracts are (a) listed in Schedule 2.4 to the Cornerstone
Disclosure Letter, (b) unmodified except as described therein and (c) in full
force and effect. To the Knowledge of Cornerstone (as defined herein), the other
parties to any such agreement, document or contract which is of a material
nature are not in material breach of any of their respective obligations under
such agreements, documents or contracts.

     2.5 Authority; Noncontravention; Consents.

     (a) Cornerstone has the requisite corporate power and authority to enter
into this Agreement and, subject to the requisite Cornerstone stockholder
approval of the Merger Agreement and the Merger and any other matters reasonably
and timely requested by any other party to effectuate the transactions
contemplated by this Agreement (collectively, the "Cornerstone Stockholder
Approvals"), to consummate the transactions contemplated by this Agreement to
which Cornerstone is a party. The execution and delivery of this Agreement by
Cornerstone and the consummation by Cornerstone of the transactions contemplated
by this Agreement to which Cornerstone is a party have been duly authorized by
all
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<PAGE>   249

necessary action on the part of Cornerstone, except for and subject to the
Cornerstone Stockholder Approvals and the Cornerstone Partner Approvals. This
Agreement has been duly executed and delivered by Cornerstone and constitutes a
valid and binding obligation of Cornerstone, enforceable against Cornerstone in
accordance with and subject to its terms, subject to applicable bankruptcy,
insolvency, moratorium or other similar laws relating to creditors' rights and
general principles of equity.

     (b) Cornerstone Partnership has the requisite partnership power and
authority to enter into this Agreement and, subject to the requisite Cornerstone
Partner Approvals, to consummate the transactions contemplated by this Agreement
to which Cornerstone Partnership is a party. The execution and delivery of this
Agreement by Cornerstone Partnership and the consummation by Cornerstone
Partnership of the transactions contemplated by this Agreement to which
Cornerstone Partnership is a party have been duly authorized by all necessary
action on the part of Cornerstone Partnership, except for and subject to the
Cornerstone Stockholder Approvals and the Cornerstone Partner Approvals. This
Agreement has been duly executed and delivered by Cornerstone Partnership and
constitutes a valid and binding obligation of Cornerstone Partnership,
enforceable against Cornerstone Partnership in accordance with and subject to
its terms, subject to applicable bankruptcy, insolvency, moratorium or other
similar laws relating to creditors' rights and general principles of equity.

     (c) Except as set forth in Schedule 2.5(c)(1) to the Cornerstone Disclosure
Letter, the execution and delivery of this Agreement by Cornerstone do not, and
the consummation of the transactions contemplated by this Agreement to which
Cornerstone is a party and compliance by Cornerstone with the provisions of this
Agreement will not, conflict with, or result in any violation of, or default
(with or without notice or lapse of time, or both) under, or give rise to a
right of termination, cancellation or acceleration of any material obligation or
to material loss of a benefit under, or result in the creation of any Lien upon
any of the properties or assets of Cornerstone or any Cornerstone Subsidiary
under, (i) the Cornerstone Articles or Cornerstone Bylaws or the comparable
charter or organizational documents or partnership, operating, or similar
agreement (as the case may be) of any Cornerstone Subsidiary or Cornerstone
Non-controlled Subsidiary, each as amended or supplemented, (ii) any loan or
credit agreement, note, bond, mortgage, indenture, merger or other acquisition
agreement, reciprocal easement agreement, lease or other agreement, instrument,
permit, concession, franchise or license applicable to Cornerstone or any
Cornerstone Subsidiary or Cornerstone Non-controlled Subsidiary or their
respective properties or assets or (iii) subject to the governmental filings and
other matters referred to in the following sentence, any judgment, order,
decree, statute, law, ordinance, rule or regulation (collectively, "Laws")
applicable to Cornerstone or any Cornerstone Subsidiary or Cornerstone
Non-controlled Subsidiary, or their respective properties or assets, other than,
in the case of clause (ii) or (iii), any such conflicts, violations, defaults,
rights, loss or Liens that individually or in the aggregate would not (x) have a
Cornerstone Material Adverse Effect or (y) prevent the consummation of the
transactions contemplated by this Agreement. No consent, approval, order or
authorization of, or registration, declaration or filing with, any federal,
state or local government or any court, administrative or regulatory agency or
commission or other governmental authority or agency, domestic or foreign (a
"Governmental Entity"), is required by or with respect to Cornerstone or any
Cornerstone Subsidiary or Cornerstone Non-controlled Subsidiary in connection
with the execution and delivery of this Agreement by Cornerstone or the
consummation by Cornerstone of the transactions contemplated by this Agreement,
except for (i) the filing with the Securities and Exchange Commission (the
"SEC") of the Joint Proxy Statement (as defined herein), (ii) the acceptance for
record of the Maryland Articles of Merger by the Department, (iii) the filing of
the Nevada Articles of Merger with the Secretary of State of the State of
Nevada, (iv) the filing of the Certificate of Merger with the Office of the
Secretary of State of the State of Delaware and (v) such other consents,
approvals, orders, authorizations, registrations, declarations and filings (A)
as are set forth in Schedule 2.5(c)(2) to the Cornerstone Disclosure Letter, (B)
as may be required under (w) the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended (the "HSR Act"), (x) laws requiring transfer, recordation or
gains tax filings, (y) federal, state or local environmental laws or (z) the
"blue sky" laws of various states, to the extent applicable or (C) which, if not
obtained or made, would not prevent or delay in any material respect the
consummation of any of the transactions contemplated by this Agreement or
otherwise prevent Cornerstone from performing its obligations under
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this Agreement in any material respect or reasonably be expected to have,
individually or in the aggregate, a Cornerstone Material Adverse Effect.

     2.6 SEC Documents; Financial Statements; Undisclosed Liabilities.
Cornerstone has filed all required reports, schedules, forms, statements and
other documents with the SEC since January 1, 1997 through the date hereof (the
"Cornerstone SEC Documents"). Schedule 2.6(a) to the Cornerstone Disclosure
Letter contains a complete list of all Cornerstone SEC Documents filed by
Cornerstone with the SEC under the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), between January 1, 1997 and the date of this Agreement.
All of the Cornerstone SEC Documents (other than preliminary material), as of
their respective filing dates, complied in all material respects with all
applicable requirements of the Securities Act and the Exchange Act and, in each
case, the rules and regulations promulgated thereunder applicable to such
Cornerstone SEC Documents. None of the Cornerstone SEC Documents at the time of
filing contained any untrue statement of a material fact or omitted to state any
material fact required to be stated therein or necessary in order to make the
statements therein, in light of the circumstances under which they were made,
not misleading, except to the extent such statements have been modified or
superseded by later Cornerstone SEC Documents filed and publicly available prior
to the date of this Agreement. The consolidated financial statements of
Cornerstone included in the Cornerstone SEC Documents complied as to form in all
material respects with applicable accounting requirements and the published
rules and regulations of the SEC with respect thereto, have been prepared in
accordance with generally accepted accounting principles ("GAAP") (except, in
the case of unaudited statements, as permitted by the applicable rules and
regulations of the SEC) applied on a consistent basis during the periods
involved (except as may be indicated in the notes thereto) and fairly presented
in all material respects, in accordance with the applicable requirements of GAAP
and the applicable rules and regulations of the SEC, the consolidated financial
position of Cornerstone and its Subsidiaries taken as a whole, as of the dates
thereof and the consolidated results of operations and cash flows for the
periods then ended (subject, in the case of unaudited statements, to normal
year-end audit adjustments). Except as set forth in Schedule 2.6(b) to the
Cornerstone Disclosure Letter, Cornerstone has no Subsidiaries which are not
consolidated for accounting purposes. Except for liabilities and obligations set
forth in the Cornerstone SEC Documents or in Schedule 2.6(c) to the Cornerstone
Disclosure Letter, none of Cornerstone, any Cornerstone Subsidiary or the
Cornerstone Non-controlled Subsidiary has any liabilities or obligations of any
nature (whether accrued, absolute, contingent or otherwise) required by GAAP to
be set forth on a consolidated balance sheet of Cornerstone or in the notes
thereto and which, individually or in the aggregate, would have a Cornerstone
Material Adverse Effect.

     2.7 Absence of Certain Changes or Events. Except as disclosed in the
Cornerstone SEC Documents or in Schedule 2.7 to the Cornerstone Disclosure
Letter, since the date of the most recent audited financial statements included
in Cornerstone SEC Documents (the "Cornerstone Financial Statement Date"),
Cornerstone, its Subsidiaries and the Cornerstone Non-controlled Subsidiary have
conducted their business only in the ordinary course (taking into account prior
practices, including the acquisition and disposition of properties and issuance
of securities) and there has not been (a) any material adverse change in the
business, financial condition or results of operations of Cornerstone and its
Subsidiaries taken as a whole (a "Cornerstone Material Adverse Change"), nor has
there been any occurrence or circumstance that with the passage of time would
reasonably be expected to result in a Cornerstone Material Adverse Change, (b)
except for regular quarterly distributions not in excess of $0.31 per share of
Cornerstone Common Stock or Cornerstone OP Unit and except for regular annual
distributions not in excess of $1.155 per share of Cornerstone 7% Preferred
Stock (or, in each case, with respect to the period commencing on the date
hereof and ending on the Closing Date, distributions as necessary to maintain
REIT (as defined herein) status), in each case with customary record and payment
dates, any authorization, declaration, setting aside or payment of any dividend
or other distribution (whether in cash, stock or property) with respect to the
Cornerstone Common Stock, the Cornerstone OP Units or the Cornerstone 7%
Preferred Stock, (c) any split, combination or reclassification of the
Cornerstone Common Stock, the Cornerstone OP Units or the Cornerstone 7%
Preferred Stock or any issuance or the authorization of any issuance of any
other securities in respect of, in lieu of or in substitution for, or giving the
right to acquire by exchange or exercise, shares of stock of Cornerstone or
partnership interests in Cornerstone Partnership or any issuance
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of an ownership interest in, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary, (d) any damage, destruction or loss, whether or not
covered by insurance, that has or would have a Cornerstone Material Adverse
Effect, (e) any change in accounting methods, principles or practices by
Cornerstone or any Cornerstone Subsidiary or the Cornerstone Non-controlled
Subsidiary materially affecting its assets, liabilities or business, except
insofar as may have been disclosed in Cornerstone SEC Documents or required by a
change in GAAP, or (f) any amendment of any employment, consulting, severance,
retention or any other agreement between Cornerstone and any officer or director
of Cornerstone.

     2.8 Litigation. Except as disclosed in the Cornerstone SEC Documents or in
Schedule 2.8 to the Cornerstone Disclosure Letter, and other than personal
injury and other routine tort litigation arising from the ordinary course of
operations of Cornerstone, the Cornerstone Subsidiaries and the Cornerstone Non-
controlled Subsidiary (a) which are covered by adequate insurance subject to a
reasonable deductible or retention limit or (b) for which all material costs and
liabilities arising therefrom are reimbursable pursuant to common area
maintenance or similar agreements, there is no suit, action or proceeding
pending (in which service of process has been received by an employee of
Cornerstone, a Cornerstone Subsidiary or a Cornerstone Non-controlled
Subsidiary) or, to the Knowledge of Cornerstone (as hereinafter defined),
threatened in writing against or affecting Cornerstone, or any Cornerstone
Subsidiary or Cornerstone Non-controlled Subsidiary that, individually or in the
aggregate, would reasonably be expected to (i) have a Cornerstone Material
Adverse Effect or (ii) prevent the consummation of any of the transactions
contemplated by this Agreement, nor is there any judgment, decree, injunction,
rule or order of any court or Governmental Entity or arbitrator outstanding
against Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary having, or which, insofar as reasonably can be
foreseen, in the future would have, any such effect. Notwithstanding the
foregoing, (y) Schedule 2.8 to the Cornerstone Disclosure Letter sets forth each
and every material uninsured claim, equal employment opportunity claim and claim
relating to sexual harassment and/or discrimination pending or, to the Knowledge
of Cornerstone, threatened as of the date hereof, and (z) no claim has been made
under any directors' and officers' liability insurance policy maintained at any
time by Cornerstone, any of the Cornerstone Subsidiaries or the Cornerstone
Non-controlled Subsidiary.

     2.9 Properties.

     (a) Except as provided in Schedule 2.2 or Schedule 2.9(a) to the
Cornerstone Disclosure Letter, Cornerstone or the Cornerstone Subsidiary or
Cornerstone Non-controlled Subsidiary set forth on Schedule 2.2 to the
Cornerstone Disclosure Letter owns fee simple title to or holds a leasehold
interest in each of the real properties identified in Schedule 2.2 to the
Cornerstone Disclosure Letter (the "Cornerstone Properties"), which are all of
the real estate properties owned by them, in each case (except for the Permitted
Title Exceptions (as defined herein)) free and clear of liens, mortgages or
deeds of trust, claims against title, charges which are liens, security
interests or other encumbrances on title ("Encumbrances"). Schedule 2.2 to the
Cornerstone Disclosure Letter further identifies which of the Cornerstone
Properties are owned in fee simple by Cornerstone or the Cornerstone Subsidiary
or the Cornerstone Non-controlled Subsidiary and which of the Cornerstone
Properties are subject to a ground lease. Except as set forth in Schedule 2.2 to
the Cornerstone Disclosure Letter, no other Person has any ownership interest in
any of the Cornerstone Properties, and any such ownership interest so scheduled
does not materially detract from the value of the Cornerstone Subsidiary's or
Cornerstone Non-controlled Subsidiary's (as the case may be) interest in, or
materially interfere with the present use of, any of the Cornerstone Properties
subject thereto or affected thereby. Except as set forth in Schedule 2.9(a) to
the Cornerstone Disclosure Letter, none of the Cornerstone Properties is subject
to any restriction on the sale or other disposition thereof or on the financing
or release of financing thereon. The Cornerstone Properties are not subject to
any rights of way, written agreements, laws, ordinances and regulations
affecting building use or occupancy, or reservations of an interest in title
(collectively, "Property Restrictions") or Encumbrances, except for the
following (collectively, the "Permitted Title Exceptions") (i) Property
Restrictions and Encumbrances set forth in the Cornerstone Disclosure Letter,
(ii) Property Restrictions imposed or promulgated by law or any governmental
body or authority with respect to real property,

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including zoning regulations, which do not materially adversely affect the
current use of any Cornerstone Property, (iii) Property Restrictions and
Encumbrances disclosed on existing title reports or policies or existing surveys
or subsequently granted by Cornerstone or the Cornerstone Subsidiary or
Cornerstone Non-controlled Subsidiary, which Property Restrictions and
Encumbrances, in any event, do not materially detract from the value of, or
materially interfere with the present use of, any of the Cornerstone Properties
subject thereto or affected thereby and (iv) liens for real estate taxes not yet
due and payable, mechanics', carriers', workmen's, repairmen's liens and other
Encumbrances and Property Restrictions, if any, which, individually or in the
aggregate, do not materially detract from the value of or materially interfere
with the present use of any of the Cornerstone Properties subject thereto or
affected thereby. Schedule 2.9(a) to the Cornerstone Disclosure Letter lists
each of the Cornerstone Properties which are under development as of the date of
this Agreement and describes the status of such development as of the date
hereof.

     (b) Except as provided in Schedule 2.2 or Schedule 2.9(b) to the
Cornerstone Disclosure Letter, valid policies of title insurance or fully-paid
and enforceable commitments therefor have been issued insuring the applicable
Cornerstone Subsidiary's or Cornerstone Non-controlled Subsidiary's (as the case
may be) fee simple title or leasehold estate, as the case may be, to the
Cornerstone Properties owned by it in amounts approximately equal to the
purchase price therefor paid by such Cornerstone Subsidiary or Cornerstone
Non-controlled Subsidiary, subject only to the matters disclosed above and in
the Cornerstone Disclosure Letter. Such policies are, at the date hereof, in
full force and effect. No claim has been made against any such policy.

     (c) Except as provided in Schedule 2.9(c) to the Cornerstone Disclosure
Letter, Cornerstone has no Knowledge (i) that, any certificate, permit or
license from any governmental authority having jurisdiction over any of the
Cornerstone Properties or any agreement, easement or other right which is
necessary to permit the lawful use and operation of the buildings and
improvements on any of the Cornerstone Properties or which is necessary to
permit the lawful use and operation of all driveways, roads and other means of
egress and ingress to and from any of the Cornerstone Properties has not been
obtained and is not in full force and effect, or of any pending threat of
modification or cancellation of any of the same which would have a material
adverse effect on such Cornerstone Property, (ii) of any written notice of any
violation of any federal, state or municipal law, ordinance, order, regulation
or requirement affecting any of the Cornerstone Properties issued by any
governmental authority which would have a material adverse effect on such
Cornerstone Property, (iii) of any structural defects relating to any
Cornerstone Property which would have a material adverse effect on such
Cornerstone Property, (iv) of any Cornerstone Property whose building systems
are not in working order so as to have a material adverse effect on such
Cornerstone Property, or (v) of any physical damage to any Cornerstone Property
which would have a material adverse effect on such Cornerstone Property for
which there is no insurance in effect covering the cost of the restoration.

     (d) None of Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary has received any written or published notice to the
effect that (i) any condemnation or rezoning proceedings are pending or
threatened with respect to any of the Cornerstone Properties or (ii) any zoning,
building or similar law, code, ordinance, order or regulation is or will be
violated by the continued maintenance, operation or use of any buildings or
other improvements on any of the Cornerstone Properties or by the continued
maintenance, operation or use of the parking areas which would have a material
adverse effect on such Cornerstone Property. Except as set forth in Schedule
2.9(d) to the Cornerstone Disclosure Letter, all work required to be performed,
payments required to be made and actions required to be taken prior to the date
hereof pursuant to any agreement entered into with a governmental body or
authority in connection with a site approval, zoning reclassification or other
similar action relating to any Cornerstone Properties (e.g., Local Improvement
District, Road Improvement District, Environmental Mitigation) have been
performed, paid or taken, as the case may be, and Cornerstone has no Knowledge
of any planned or proposed work, payments or actions that may be required after
the date hereof pursuant to such agreements, except as set forth in development
or operating budgets for such Cornerstone Properties delivered to EOP and EOP
Partnership prior to the date hereof

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and other than those which would not reasonably be expected to have a material
adverse effect on any of Cornerstone or the Cornerstone Subsidiaries or the
Cornerstone Non-controlled Subsidiary.

     (e) The rent rolls previously provided by Cornerstone to EOP (the
"Cornerstone Rent Roll") list each Cornerstone Space Lease (as defined herein)
in effect as of the dates set forth therein, none of which are earlier than
December 31, 1999. "Cornerstone Space Lease" means each lease or other right of
occupancy affecting or relating to a property in which Cornerstone Partnership
(or an entity in which it directly or indirectly has an interest) is the
landlord, either pursuant to the terms of the lease agreement or as successor to
any prior landlord, but excluding any ground lease. Cornerstone has made
available to EOP true, correct and complete copies of all Cornerstone Space
Leases, including all amendments, modifications, supplements, renewals,
extensions and guarantees related thereto, as of the date hereof. Except for
discrepancies that, either individually or in the aggregate, would not
reasonably be expected to have a Cornerstone Material Adverse Effect, all
information set forth in the Cornerstone Rent Roll is true, correct and complete
as of the date thereof. Except as set forth in a delinquency report made
available to EOP, none of Cornerstone, any Cornerstone Subsidiary or the
Cornerstone Non-controlled Subsidiary, on the one hand, nor, to the knowledge of
Cornerstone or Cornerstone Partnership, any other party, on the other hand, is
in monetary default under any Cornerstone Space Lease, except for such defaults
that would not reasonably be expected to have a Cornerstone Material Adverse
Effect.

     2.10 Environmental Matters.

     (a) "Environmental Law" shall mean all applicable Laws relating to the
protection of human health or safety and natural resources or the environment,
including, without limitation, Laws relating to the use, manufacturing,
generation, recycling, reuse, sale, storage, handling, transport, treatment or
disposal of any Hazardous Materials (including the Comprehensive Environmental
Response, Compensation, and Liability Act, as amended, 42 U.S.C. sec.sec. 9601
et seq. ("CERCLA")). "Hazardous Materials" shall mean substances, wastes or
materials listed, regulated or defined under any Environmental Law, and shall
include "hazardous wastes," "hazardous substances," "hazardous materials,"
petroleum or any fraction thereof, asbestos, lead-paint, urea-formaldehyde, and
polychlorinated biphenyls. "Release" shall have the meaning set forth in Section
101 of CERCLA, without regard to the exclusions set forth therein.

     (b) Except as disclosed in the Cornerstone SEC Documents or in Schedule
2.10(a) to the Cornerstone Disclosure Letter,

          (i) none of Cornerstone, any of the Cornerstone Subsidiaries or the
     Cornerstone Non-controlled Subsidiary or, to Cornerstone's Knowledge, any
     other Person has caused or permitted the presence of any Hazardous
     Materials at, on or under any of the Cornerstone Properties and none of
     Cornerstone, any of the Cornerstone Subsidiaries or the Cornerstone
     Non-controlled Subsidiary has any knowledge of the presence of any
     Hazardous Materials at, on or under any of the Cornerstone Properties, in
     each of the foregoing cases, such that the presence of such Hazardous
     Materials (including the presence of asbestos in any buildings or
     improvements at the Cornerstone Properties) would, individually or in the
     aggregate, reasonably be expected to have a Cornerstone Material Adverse
     Effect;

          (ii) except in accordance with the Environmental Permits (as defined
     herein) there have been no Releases of Hazardous Materials at, on, under or
     from (A) the Cornerstone Properties or (B) any real property previously
     owned, operated or leased by Cornerstone, the Cornerstone Subsidiaries, or
     the Cornerstone Non-controlled Subsidiary (the "Former Cornerstone
     Properties") during the period of such ownership, operation or tenancy, and
     none of Cornerstone, any of the Cornerstone Subsidiaries or the Cornerstone
     Non-controlled Subsidiary has any knowledge of any Releases of Hazardous
     Materials having occurred or presently occurring at, on, under or from the
     Cornerstone Properties or the Former Cornerstone Properties, which would,
     individually or in the aggregate, reasonably be expected to have a
     Cornerstone Material Adverse Effect;

          (iii) Cornerstone, the Cornerstone Subsidiaries and the Cornerstone
     Non-controlled Subsidiary have not failed to comply with all Environmental
     Laws, and none of Cornerstone, any of the Cornerstone Subsidiaries or the
     Cornerstone Non-controlled Subsidiary has any liability under the

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     Environmental Laws, except to the extent that any such failure to comply or
     any such liability, individually or in the aggregate, would not reasonably
     be expected to have a Cornerstone Material Adverse Effect; and

          (iv) Cornerstone, the Cornerstone Subsidiaries and the Cornerstone
     Non-controlled Subsidiary have been duly issued, and currently have and
     will maintain through the Closing Date, all permits, licenses, certificates
     and approvals required under any Environmental Law (collectively, the
     "Environmental Permits") necessary to operate their businesses as currently
     operated except where the failure to obtain and maintain such Environmental
     Permit would not have a material adverse effect on the Cornerstone
     Property. Cornerstone, the Cornerstone Subsidiaries and the Cornerstone
     Non-controlled Subsidiary have timely filed applications for all
     Environmental Permits. All of the Environmental Permits are transferable
     and none require consent, notification or other action to remain in full
     force and effect following consummation of the transactions contemplated
     hereby.

     (c) Cornerstone has previously delivered or made available to EOP complete
copies of all material information, documents and reports, including, without
limitation, environmental investigations and testing or analysis that are in the
possession or control of any of Cornerstone, the Cornerstone Subsidiaries and
the Cornerstone Non-controlled Subsidiary and which relate to compliance with
Environmental Laws by any of them or to the past or current environmental
condition of the Cornerstone Properties.

     2.11 Related Party Transactions. Set forth in Schedule 2.11 to the
Cornerstone Disclosure Letter is a list of all material arrangements, agreements
and contracts entered into by Cornerstone, any Cornerstone Subsidiary and the
Cornerstone Non-controlled Subsidiary with (a) any investment banker or
financial advisor, (b) any person who is an officer, director or Affiliate (as
defined herein) of Cornerstone or any Subsidiary or the Cornerstone
Non-controlled Subsidiary, any relative of any of the foregoing or any entity of
which any of the foregoing is an Affiliate or (c) any person who acquired
Cornerstone Common Stock, Cornerstone OP Units or Cornerstone 7% Preferred Stock
in a private placement, in each case which remain in effect and are not
otherwise disclosed in the SEC Documents. Such documents, copies of all of which
have previously been delivered or made available to EOP, are listed in Schedule
2.11 to the Cornerstone Disclosure Letter. As used in this Agreement, the term
"Affiliate" shall have the same meaning as such term is defined in Rule 405
promulgated under the Securities Act.

     2.12 Employee Benefits. As used herein, the term "Employee Plan" includes
any pension, retirement, savings, disability, medical, dental, health, life,
death benefit, group insurance, profit sharing, deferred compensation, stock
option, bonus, incentive, vacation pay, tuition reimbursement, severance pay, or
other employee benefit plan, trust, agreement, contract, agreement, policy or
commitment (including, without limitation, any pension plan, as defined in
Section 3(2) of the Employee Retirement Income Security Act of 1974, as amended,
and the rules and regulations promulgated thereunder ("ERISA") ("Pension Plan"),
and any welfare plan as defined in Section 3(1) of ERISA ("Welfare Plan")),
whether any of the foregoing is funded, insured or self-funded, written or oral,
(i) sponsored or maintained by Cornerstone, any Cornerstone Subsidiary or the
Cornerstone Non-controlled Subsidiary (each, a "Controlled Group Member") and
covering any Controlled Group Member's active or former employees (or their
beneficiaries), (ii) to which any Controlled Group Member is a party or by which
any Controlled Group Member (or any of the rights, properties or assets thereof)
is bound or (iii) with respect to which any current Controlled Group Member may
otherwise have any material liability (whether or not such Controlled Group
Member still maintains such Employee Plan). Each Employee Plan is listed on
Schedule 2.12 to the Cornerstone Disclosure Letter. Except as disclosed in
Schedule 2.12 to the Cornerstone Disclosure Letter, with respect to the Employee
Plans:

     (a) No Controlled Group Member has any continuing liability under any
Welfare Plan which provides for continuing benefits or coverage for any
participant or any beneficiary of a participant after such participant's
termination of employment, except as may be required by Section 4980B of the
Code or Section 601 (et seq.) of ERISA, or under any applicable state law, and
at the expense of the participant or the beneficiary of the participant.

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     (b) Each Employee Plan complies in all material respects with the
applicable requirements of ERISA and any other applicable law governing such
Employee Plan, and, to the Knowledge of Cornerstone, each Employee Plan has at
all times been properly administered in all material respects in accordance with
all such requirements of law, and in accordance with its terms and the terms of
any applicable collective bargaining agreement to the extent consistent with all
such requirements of law. Each Pension Plan which is intended to be qualified is
qualified under Section 401(a) of the Code, has received a favorable
determination letter from the IRS stating that such Plan meets the requirements
of Section 401(a) of the Code and that the trust associated with such Plan is
tax-exempt under Section 501(a) of the Code and, to the Knowledge of
Cornerstone, no event has occurred which would jeopardize the qualified status
of any such plan or the tax exempt status of any such trust under Sections
401(a) and Section 501(a) of the Code, respectively. No lawsuits, claims (other
than routine claims for benefits) or complaints to, or by, any person or
governmental entity have been filed, are pending or, to the Knowledge of
Cornerstone, threatened with respect to any Employee Plan and, to the Knowledge
of Cornerstone, there is no fact or contemplated event which would be expected
to give rise to any such lawsuit, claim (other than routine claims for benefits)
or complaint with respect to any Pension Plan. Without limiting the foregoing,
the following are true with respect to each Employee Plan:

          (i) all Controlled Group Members have complied in all material
     respects with the reporting and disclosure requirements of ERISA, the Code,
     or both, with respect to each Employee Plan and no Controlled Group Member
     has incurred any material liability in connection with such reporting or
     disclosure;

          (ii) all contributions and payments with respect to Employee Plans
     that are required to be made by a Controlled Group Member with respect to
     periods ending on or before the Closing Date (including periods from the
     first day of the current plan or policy year to the Closing Date) have
     been, or will be, made or accrued before the Closing Date in accordance
     with the appropriate plan document, actuarial report, collective bargaining
     agreements or insurance contracts or arrangements or as otherwise required
     by ERISA or the Code; and

          (iii) with respect to each such Employee Plan, to the extent
     applicable, Cornerstone has delivered to or has made available to EOP true
     and complete copies of (A) plan documents, or any and all other documents
     that establish the existence of the plan, trust, arrangement, contract,
     policy or commitment and all amendments thereto, (B) the most recent
     determination letter, if any, received from the IRS, (C) the three most
     recent Form 5500 Annual Reports (and all schedules and reports relating
     thereto) and actuarial reports and (D) all related trust agreements,
     insurance contract or other funding agreements that implement each such
     Employee Plan.

     (c) With respect to each Employee Plan, to the Knowledge of Cornerstone,
there has not occurred, and no person or entity is contractually bound to enter
into, any "prohibited transaction" within the meaning of Section 4975(c) of the
Code or Section 406 of ERISA, which transaction is not exempt under Section
4975(d) of the Code or Section 408 of ERISA and which could subject Cornerstone
or any Controlled Group Member to material liability.

     (d) No Controlled Group Member has maintained or been obligated to
contribute to any Employee Plan subject to Code Section 412 or Title IV of
ERISA. No Employee Plan subject to Code Section 412 or Title IV of ERISA has
been terminated.

     (e) With respect to each Pension Plan maintained by any Controlled Group
Member, such Plan provides the Plan Sponsor the authority to amend or terminate
the Plan at any time, subject to applicable requirements of ERISA and the Code.

     2.13 Employee Policies. The employee handbooks of Cornerstone, the
Cornerstone Subsidiaries and the Cornerstone Non-controlled Subsidiary currently
in effect are attached as Schedule 2.13 to the Cornerstone Disclosure Letter and
fairly and accurately summarize all material employee policies, vacation
policies and payroll policies.

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     2.14 Taxes.

     (a) Each of Cornerstone, the Cornerstone Subsidiaries and the Cornerstone
Non-controlled Subsidiary (A) has filed all Tax returns and reports required to
be filed by it (after giving effect to any filing extension properly granted by
a Governmental Entity having authority to do so) and all such returns and
reports are accurate and complete in all material respects, (B) has paid (or
Cornerstone has paid on its behalf) all Taxes (as defined herein) shown on such
returns and reports as required to be paid by it, and (C) has complied in all
material respects with all applicable laws, rules and regulations relating to
the payment and withholding of Taxes (including, without limitation, withholding
of Taxes pursuant to Sections 1441, 1442, 1445, 3121, and 3402 of the Code or
similar provisions under any foreign laws) and has, within the time period
prescribed by law, withheld and paid over to the proper governmental entities
all amounts required to be so withheld and paid over under applicable laws and
regulations, except, with respect to all of the foregoing, where the failure to
file such tax returns and reports or failure to pay such Taxes or failure to
comply with such withholding requirements would not reasonably be expected to
have a Cornerstone Material Adverse Effect. The most recent audited financial
statements contained in the Cornerstone SEC Documents reflect an adequate
reserve for all material Taxes payable by Cornerstone, the Cornerstone
Subsidiaries and the Cornerstone Non-controlled Subsidiary for all taxable
periods and portions thereof through the date of such financial statements.
Since the Cornerstone Financial Statement Date, Cornerstone has incurred no
liability for Taxes under Sections 857(b), 860(c) or 4981 of the Code, including
without limitation any Tax arising from a prohibited transaction described in
Section 857(b)(6) of the Code, and none of Cornerstone, any Cornerstone
Subsidiary or the Cornerstone Non-controlled Subsidiary has incurred any
material liability for Taxes other than in the ordinary course of business. No
event has occurred, and no condition or circumstance exists, which presents a
material risk that any material Tax described in the preceding sentences will be
imposed upon Cornerstone, any Cornerstone Subsidiary, or the Cornerstone
Non-controlled Subsidiary. None of Cornerstone, any Cornerstone Subsidiary or
the Cornerstone Non-controlled Subsidiary is the subject of any audit,
examination, or other proceeding in respect of federal income Taxes, and to
Cornerstone's Knowledge, no audit, examination or other proceeding in respect of
federal income Taxes involving any of Cornerstone, any Cornerstone Subsidiary,
or the Cornerstone Non-controlled Subsidiary is being considered by any Tax
authority. To the Knowledge of Cornerstone, no deficiencies for any Taxes have
been proposed, asserted or assessed against Cornerstone, any Cornerstone
Subsidiary or the Cornerstone Non-controlled Subsidiary, and no requests for
waivers of the time to assess any such Taxes are pending. As used in this
Agreement, "Taxes" shall include all taxes, charges, fees, levies and other
assessments, including, without limitation, income, gross receipts, excise,
property, sales, withholding (including, without limitation, dividend
withholding and withholding required pursuant to Sections 1445 and 1446 of the
Code), social security, occupation, use, service, license, payroll, franchise,
transfer and recording taxes, fees and charges, including estimated taxes,
imposed by the United States or any taxing authority (domestic or foreign),
whether computed on a separate, consolidated, unitary, combined or any other
basis, and any interest, fines, penalties or additional amounts attributable to,
or imposed upon, or with respect to any such taxes, charges, fees, levies or
other assessments.

     (b) Cornerstone (i) for all taxable years for which the Internal Revenue
Service could assert a tax liability, has been subject to taxation as a real
estate investment trust (a "REIT") within the meaning of Section 856 of the Code
and has satisfied all requirements to qualify as a REIT for all such years, (ii)
has operated since December 31, 1999 to the date of this representation, and
intends to continue to operate, in such a manner as to qualify as a REIT for the
taxable year ending on the earlier of December 31, 2000 or the Closing Date and,
if later, for the taxable year of Cornerstone ending on the Closing Date, and
(iii) has not taken or omitted to take any action which would reasonably be
expected to result in a challenge to its status as a REIT and, to Cornerstone's
Knowledge, no such challenge is pending or threatened. Each Cornerstone
Subsidiary which is a partnership, joint venture or limited liability company
(i) has been since its formation and continues to be treated for federal income
tax purposes as a partnership and not as a corporation or an association taxable
as a corporation and (ii) has not since the later of its formation or the
acquisition by Cornerstone of a direct or indirect interest therein, owned any
assets (including, without limitation, securities) that would cause Cornerstone
to violate Section
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856(c)(4) of the Code. Cornerstone Partnership is not a publicly-traded
partnership within the meaning of Section 7704(b) of the Code that is taxable as
a corporation pursuant to Section 7704(a) of the Code. Each Cornerstone
Subsidiary which is a corporation has been since its formation a qualified REIT
subsidiary under Section 856(i) of the Code. Neither Cornerstone nor any
Cornerstone Subsidiary holds any asset (x) the disposition of which would be
subject to rules similar to Section 1374 of the Code as a result of an election
under IRS Notice 88-19 or Temporary Treas. Reg. sec.1.337(d)-5T or (y) which is
subject to a consent filed pursuant to Section 341(f) of the Code and the
regulations thereunder.

     2.15 No Payments to Employees, Officers or Directors. Schedule 2.15 to the
Cornerstone Disclosure Letter contains a true and complete list of all
arrangements, agreements or plans pursuant to which cash and non-cash payments
which will become payable (and the maximum aggregate amount which may be payable
thereunder) to each employee, officer or director of Cornerstone, any
Cornerstone Subsidiary or the Cornerstone Non-controlled Subsidiary as a result
of the Merger or a termination of service subsequent to the consummation of the
Merger. Except as described in Schedule 2.15 to the Cornerstone Disclosure
Letter, or as otherwise provided for in this Agreement, there is no employment
or severance contract, or other agreement requiring payments, cancellation of
indebtedness or other obligation to be made on a change of control or otherwise
as a result of the consummation of any of the transactions contemplated by this
Agreement or as a result of a termination of service subsequent to the
consummation of any of the transactions contemplated by this Agreement, with
respect to any employee, officer or director of Cornerstone, any Cornerstone
Subsidiary or the Cornerstone Non-controlled Subsidiary. There is no agreement
or arrangement with any employee, officer or other service provider under which
Cornerstone, any Cornerstone Subsidiary or any Cornerstone Non-controlled
Subsidiary has agreed to pay any tax that might be owed under Section 4999 of
the Code with respect to payments to such individuals.

     2.16 Broker; Schedule of Fees and Expenses. No broker, investment banker,
financial advisor or other person, other than Lazard Freres & Co. L.L.C. the
fees and expenses of which are described in the engagement letter dated January
28, 2000, between Lazard Freres & Co. L.L.C. and Cornerstone, a true, correct
and complete copy of which has previously been given to EOP, is entitled to any
broker's, finder's, financial advisor's or other similar fee or commission in
connection with the transactions contemplated hereby based upon arrangements
made by or on behalf of Cornerstone or any Cornerstone Subsidiary.

     2.17 Compliance with Laws. None of Cornerstone, any Cornerstone Subsidiary
or the Cornerstone Non-controlled Subsidiary has violated or failed to comply
with any statute, law, ordinance, regulation, rule, judgment, decree or order of
any Governmental Entity applicable to its business, properties or operations,
except to the extent that such violation or failure would not reasonably be
expected to have a Cornerstone Material Adverse Effect.

     2.18 Contracts; Debt Instruments.

     (a) None of Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary has received a written notice that it is in violation
of or in default under (nor to the Knowledge of Cornerstone does there exist any
condition which upon the passage of time or the giving of notice or both would
cause such a violation of or default under) any material loan or credit
agreement, note, bond, mortgage, indenture, lease, permit, concession,
franchise, license or any other material contract, agreement, arrangement or
understanding, to which it is a party or by which it or any of its properties or
assets is bound, nor to the Knowledge of Cornerstone does such a violation or
default exist, except to the extent that such violation or default, individually
or in the aggregate, would not reasonably be expected to have a Cornerstone
Material Adverse Effect.

     (b) Except for any of the following expressly identified in Cornerstone SEC
Documents, Schedule 2.18(b) to the Cornerstone Disclosure Letter sets forth a
list of each material loan or credit agreement, note, bond, mortgage, indenture
and any other agreement or instrument pursuant to which any Indebtedness (as
defined herein) of Cornerstone, the Cornerstone Subsidiaries and the Cornerstone
Non-controlled Subsidiary, other than Indebtedness payable to Cornerstone, a
Cornerstone Subsidiary or a Cornerstone Non-controlled Subsidiary, is
outstanding or may be incurred. For purposes of this Section 2.18,
"Indebtedness" shall mean (i) indebtedness for borrowed money, whether secured
or unsecured,

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(ii) obligations under conditional sale or other title retention agreements
relating to property purchased by such person, (iii) capitalized lease
obligations, (iv) obligations under interest rate cap, swap, collar or similar
transaction or currency hedging transactions (valued at the termination value
thereof) and (v) guarantees of any such indebtedness of any other person.

     (c) To the extent not set forth in response to the requirements of Section
2.18(b), Schedule 2.18(c) to the Cornerstone Disclosure Letter sets forth each
interest rate cap, interest rate collar, interest rate swap, currency hedging
transaction, and any other agreement relating to a similar transaction to which
Cornerstone, any Cornerstone Subsidiary or the Cornerstone Non-controlled
Subsidiary is a party or an obligor with respect thereto.

     (d) Except as set forth in Schedule 2.18(d) of the Cornerstone Disclosure
Letter, none of Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary is a party to any agreement which would restrict any
of them from prepaying any of their Indebtedness without penalty or premium at
any time or which requires any of them to maintain any amount of Indebtedness
with respect to any of the Cornerstone Properties.

     (e) Except as set forth in Schedule 2.18(e) to the Cornerstone Disclosure
Letter, none of Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary is a party to any agreement relating to the management
of any Cornerstone Property by any Person other than Cornerstone, a Cornerstone
Subsidiary or a Cornerstone Non-controlled Subsidiary.

     (f) None of Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary is a party to any agreement pursuant to which
Cornerstone, any Cornerstone Subsidiary or the Cornerstone Non-controlled
Subsidiary manages or provides services with respect to any real properties
other than Cornerstone Properties, except for the agreements described in
Schedule 2.18(f) to the Cornerstone Disclosure Letter.

     (g) Cornerstone has delivered to EOP prior to the date of this Agreement a
true and complete capital budget for the year 2000 relating to budgeted capital
improvements and development. Schedule 2.18(g) to the Cornerstone Disclosure
Letter lists all material agreements entered into by Cornerstone, each of the
Cornerstone Subsidiaries and the Cornerstone Non-controlled Subsidiary relating
to the development or construction of, or additions or expansions to, any
Cornerstone Real Properties (or any properties with respect to which Cornerstone
has executed as of the date of this Agreement a purchase agreement or other
similar agreement) which are currently in effect and under which Cornerstone or
any of the Cornerstone Subsidiaries or the Cornerstone Non-controlled Subsidiary
currently has, or expects to incur, an obligation in excess of $250,000 in the
aggregate. True, correct and complete copies of such agreements have previously
been delivered or made available to EOP.

     (h) Schedule 2.18(h) to the Cornerstone Disclosure Letter lists all
agreements entered into by Cornerstone, any Cornerstone Subsidiary or the
Cornerstone Non-controlled Subsidiary providing for the sale of, or option to
sell, any Cornerstone Properties or the purchase of, or option to purchase, by
Cornerstone, any Cornerstone Subsidiary or the Cornerstone Non-controlled
Subsidiary, on the one hand, or the other party thereto, on the other hand, any
real estate which are currently in effect.

     (i) Except as set forth in Schedule 2.18(i) to the Cornerstone Disclosure
Letter, none of Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary has any material continuing contractual liability (A)
for indemnification or otherwise under any agreement relating to the sale of
real estate previously owned, whether directly or indirectly, by Cornerstone,
any Cornerstone Subsidiary or Cornerstone Non-controlled Subsidiary or (B) to
pay any additional purchase price for any of the Cornerstone Properties.

     (j) Except as set forth in Schedule 2.18(j) to the Cornerstone Disclosure
Letter, none of Cornerstone, any Cornerstone Subsidiary or the Cornerstone
Non-controlled Subsidiary has entered into or is subject, directly or
indirectly, to any "Tax Protection Agreements." As used herein, a Tax Protection
Agreement is an agreement, oral or written, (A) that has as one of its purposes
to permit a person or entity to take the position that such person or entity
could defer federal taxable income that otherwise
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might have been recognized upon a transfer of property to the Cornerstone
Partnership or any other Cornerstone Subsidiary that is treated as a partnership
for federal income tax purposes, and that (i) prohibits or restricts in any
manner the disposition of any assets of Cornerstone, any Cornerstone Subsidiary
or the Cornerstone Non-controlled Subsidiary, (ii) requires that Cornerstone,
any Cornerstone Subsidiary or the Cornerstone Non-controlled Subsidiary
maintain, or put in place, or replace, indebtedness, whether or not secured by
one or more of the Cornerstone Properties, or (iii) requires that Cornerstone,
any Cornerstone Subsidiary or the Cornerstone Non-controlled Subsidiary offer to
any person or entity at any time the opportunity to guarantee or otherwise
assume, directly or indirectly (including, without limitation, through a
"deficit restoration obligation," indemnification agreement or other similar
arrangement), the risk of loss for federal income tax purposes for indebtedness
or other liabilities of Cornerstone, any Cornerstone Subsidiary or the
Cornerstone Non-controlled Subsidiary, (B) that specifies or relates to a method
of taking into account book-tax disparities under Section 704(c) of the Code
with respect to one or more assets of Cornerstone or a Cornerstone Subsidiary,
or (C) that requires a particular method for allocating one or more liabilities
of Cornerstone or any Cornerstone Subsidiary under Section 752 of the Code. None
of Cornerstone, any Cornerstone Subsidiary or the Cornerstone Non-controlled
Subsidiary is in violation of or in default under any Tax Protection Agreement.

     (k) Except as set forth in Schedule 2.18(k) to the Cornerstone Disclosure
Letter and for the Confidentiality Agreement, dated January 13, 2000 between
Cornerstone and EOP (the "Confidentiality Agreement") and other confidentiality
agreements entered into in the ordinary course of business, neither Cornerstone
nor any Cornerstone Subsidiary or the Cornerstone Non-controlled Subsidiary is a
party to any confidentiality, standstill, lock-up or voting agreement.

     2.19 Opinion of Financial Advisor. Cornerstone has received the written
opinion of Lazard Freres & Co. L.L.C. Cornerstone's financial advisor, to the
effect that the proposed consideration to be received by the holders of
Cornerstone Common Stock is fair to such holders from a financial point of view.

     2.20 State Takeover Statutes. Cornerstone has taken all action necessary to
exempt the transactions contemplated by this Agreement between EOP and
Cornerstone and its Affiliates from the operation of any "fair price,"
"moratorium," "control share acquisition" or any other anti-takeover statute or
similar statute enacted under the laws of the State of Nevada and the State of
Delaware or federal laws of the United States or similar statute or regulation
(a "Takeover Statute").

     2.21 Investment Company Act of 1940. None of Cornerstone, any Cornerstone
Subsidiary or the Cornerstone Non-controlled Subsidiary is, or at the Effective
Time will be, required to be registered under the Investment Company Act of
1940, as amended (the "1940 Act").

     2.22 Definition of "Knowledge of Cornerstone". As used in this Agreement,
the phrase "Knowledge of Cornerstone" (or words of similar import) means the
actual knowledge of those individuals identified in Schedule 2.22 to the
Cornerstone Disclosure Letter.

     2.23 Required Stockholder Approvals and Partner Approvals. The affirmative
vote of the holders of at least a majority of the outstanding Cornerstone Common
Stock and the holders of at least a majority of the outstanding Cornerstone 7%
Preferred Stock are the only votes of the holders of any class or series of
Cornerstone capital stock necessary or required under this Agreement or under
applicable law to approve the Merger and this Agreement. The approval of
Cornerstone and the affirmative vote of at least a majority of all Cornerstone
limited partner interests entitled to be cast, voting in accordance with the
Cornerstone Partnership Agreement, is the only vote of the holders of any class
or series of Cornerstone Partnership's partnership interests necessary or
required under this Agreement or under applicable law to approve the Merger, the
withdrawal of Cornerstone as general partner and the Partnership Merger.

                                   ARTICLE 3

           REPRESENTATIONS AND WARRANTIES OF EOP AND EOP PARTNERSHIP

     Except as set forth in the EOP SEC Documents (as defined herein) or in the
letter of even date herewith signed by the President or an Executive Vice
President of EOP and delivered to Cornerstone

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prior to the execution hereof (the "EOP Disclosure Letter"), EOP and EOP
Partnership represent and warrant to Cornerstone and Cornerstone Partnership as
follows:

     3.1 Organization, Standing and Power of EOP. EOP is a real estate
investment trust duly organized, validly existing and in good standing under the
laws of Maryland and has all requisite power and authority to own, operate,
lease and encumber its properties and carry on its business as now being
conducted. EOP is duly qualified or licensed to do business as a foreign trust
and is in good standing in each jurisdiction in which the nature of its business
or the ownership or leasing of its properties makes such qualification or
licensing necessary, other than in such jurisdictions where the failure to be so
qualified or licensed, individually or in the aggregate, would not reasonably be
expected to have a material adverse effect on the business, properties, assets,
financial condition or results of operations of EOP and the Subsidiaries of EOP
(collectively, "EOP Subsidiaries"), taken as a whole (an "EOP Material Adverse
Effect"). EOP has delivered to Cornerstone complete and correct copies of the
EOP Declaration of Trust (as the same is proposed to be modified by each of the
Proposed EOP Charter Amendments (as defined herein)) and the EOP Bylaws, as
amended or supplemented to the date of this Agreement.

     3.2 EOP Subsidiaries.

     (a) Schedule 3.2(a) to the EOP Disclosure Letter sets forth (i) each EOP
Subsidiary and each entity in which EOP holds non-voting equity securities (but
no voting equity securities) (collectively, the "EOP Non-controlled
Subsidiaries"), (ii) the ownership interest therein of EOP, (iii) if not wholly
owned by EOP, the identity and ownership interest of each of the other owners of
such EOP Subsidiary, (iv) each office property and other commercial property
owned by such Subsidiary, and (v) if not wholly owned by such Subsidiary, the
identity and ownership interest of each of the other owners of such property.

     (b) Except as set forth in Schedule 3.2(b) to the EOP Disclosure Letter,
(i) all the outstanding shares of capital stock of each EOP Subsidiary and each
EOP Non-controlled Subsidiary that is a corporation have been duly authorized,
validly issued and are (A) fully paid and nonassessable and not subject to
preemptive rights, (B) owned by EOP or by another EOP Subsidiary and (C) owned
free and clear of all Liens and (ii) all equity interests in each EOP Subsidiary
that is a partnership, joint venture, limited liability company or trust which
are owned by EOP, by another EOP Subsidiary or by EOP and another EOP Subsidiary
are owned free and clear of all Liens other than pledges, if any, contained in
organizational documents of such EOP Subsidiary and given to secure performance
thereunder. Each EOP Subsidiary that is a corporation is duly incorporated,
validly existing and in good standing under the laws of its jurisdiction of
incorporation and has the requisite corporate power and authority to own,
operate, lease and encumber its properties and carry on its business as now
being conducted, and each EOP Subsidiary that is a partnership, limited
liability company or trust is duly organized, validly existing and in good
standing under the laws of its jurisdiction of organization and has the
requisite power and authority to own, operate, lease and encumber its properties
and carry on its business as now being conducted. Each EOP Subsidiary is duly
qualified or licensed to do business and is in good standing in each
jurisdiction in which the nature of its business or the ownership or leasing of
its properties makes such qualification or licensing necessary, other than in
such jurisdictions where the failure to be so qualified or licensed,
individually or in the aggregate, would not reasonably be expected to have an
EOP Material Adverse Effect. Complete and correct copies of the Articles of
Incorporation, Bylaws, organization documents and partnership, joint venture and
operating agreements of each EOP Subsidiary, as amended to the date of this
Agreement, have been previously delivered or made available to Cornerstone. No
effective amendment has been made to the EOP Partnership Agreement since January
31, 2000.

     3.3 Capital Structure.

     (a) The authorized shares of beneficial interest of EOP consist of
750,000,000 EOP Common Shares, 248,812,828 of which were issued and outstanding
as of January 31, 2000, and 100,000,000 preferred shares of beneficial interest,
18,562,900 of which were issued or outstanding as of January 31, 2000
(collectively, the "EOP Preferred Shares").

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<PAGE>   261

     (b) Set forth in Schedule 3.3(b) to the EOP Disclosure Letter is a true and
complete list of the following: (i) each qualified or nonqualified option to
purchase EOP's shares of beneficial interest granted under the Employee Share
Option and Restricted Share Plan or any other formal or informal arrangement
(collectively, the "EOP Options"); and (ii) all other warrants or other rights
to acquire EOP's shares of beneficial interest, all share appreciation rights,
phantom shares, dividend equivalents, performance units and performance shares
which are outstanding on the date of this Agreement. Schedule 3.3(b) to the EOP
Disclosure Letter sets forth the EOP Options granted to EOP's Chief Executive
Officer and four other most highly compensated officers, the date of each grant,
the status of each EOP Option as qualified or nonqualified under Section 422 of
the Code, the number of EOP Common Shares subject to each EOP Option, the number
and type of EOP's Common Shares subject to EOP Options that are currently
exercisable, the exercise price per share, and the number and type of such
shares subject to share appreciation rights. On the date of this Agreement,
except as set forth in this Section 3.3 or in Schedule 3.3(b) to the EOP
Disclosure Letter, no shares of beneficial interest of EOP were outstanding or
reserved for issuance (except for EOP Common Shares reserved for issuance upon
redemption of EOP OP Units).

     (c) All outstanding shares of beneficial interest of EOP are duly
authorized, validly issued, fully paid and nonassessable and not subject to
preemptive rights. There are no bonds, debentures, notes or other indebtedness
of EOP having the right to vote (or convertible into, or exchangeable for,
securities having the right to vote) on any matters on which shareholders of EOP
may vote.

     (d) Except (i) as set forth in this Section 3.3 or in Schedule 3.3(d) to
the EOP Disclosure Letter and (ii) EOP OP Units, which may be redeemed for EOP
Common Shares, as of the date of this Agreement, there are no outstanding
securities, options, warrants, calls, rights, commitments, agreements,
arrangements or undertakings of any kind to which EOP or any EOP Subsidiary is a
party or by which such entity is bound, obligating EOP or any EOP Subsidiary to
issue, deliver or sell, or cause to be issued, delivered or sold, additional
shares of beneficial interest, voting securities or other ownership interests of
EOP or any EOP Subsidiary or obligating EOP or any EOP Subsidiary to issue,
grant, extend or enter into any such security, option, warrant, call, right,
commitment, agreement, arrangement or undertaking (other than to EOP or an EOP
Subsidiary).

     (e) As of January 31, 2000, 282,476,889 EOP OP Units, 8,000,000 8.98%
Series A Preferred Units of Limited Partnership Interest, 6,000,000 5.25% Series
B Preferred Units of Limited Partnership Interest, and 4,562,900 8 5/8% Series C
Preferred Units of Limited Partnership Interest (collectively, the "EOP
Preferred Units") are validly issued and outstanding, fully paid and
nonassessable and not subject to preemptive rights, of which 248,812,828 EOP OP
Units and all of the EOP Preferred Units are owned by EOP and EOP Subsidiaries.
Schedule 3.3(e) to the EOP Disclosure Schedule sets forth the name of each
holder of EOP OP Units and the number of EOP OP Units owned by each such holder
as of the date of this Agreement. The EOP OP Units and EOP Preferred Units are
subject to no restrictions except as set forth in the EOP Partnership Agreement.
EOP Partnership has not issued or granted and is not a party to any outstanding
commitments of any kind relating to, or any presently effective agreements or
understandings with respect to, interests in EOP Partnership, whether issued or
unissued, or securities convertible or exchangeable into interests in EOP
Partnership.

     (f) All dividends on EOP Common Shares and all distributions on EOP OP
Units and EOP Preferred Units, which have been declared prior to the date of
this Agreement have been paid in full, except that the dividends payable on EOP
Common Shares (along with the corresponding distributions payable on EOP OP
Units) which were declared on February 1, 2000 and are payable on April 14, 2000
have not yet been paid.

     (g) The EOP Common Shares and the EOP Preferred Shares to be issued by EOP,
and the EOP OP Units to be issued by the EOP Partnership pursuant to this
Agreement have been duly authorized for issuance, and upon issuance will be duly
and validly issued, fully paid and nonassessable.

     3.4 Other Interests. Except for interests in the EOP Subsidiaries and
certain other entities as set forth in Schedule 3.2(a), 3.2(b) or 3.4(a) to the
EOP Disclosure Letter (the "EOP Other Interests"), neither

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<PAGE>   262

EOP nor any of its Subsidiaries owns directly or indirectly any interest or
investment (whether equity or debt) in any corporation, partnership, joint
venture, business, trust or other entity (other than investments in short-term
investment securities). With respect to such other interests, EOP or EOP
Partnership is a partner or shareholder in good standing, and owns such
interests free and clear of all Liens other than pledges, if any, contained in
organizational documents of such EOP Other Interests and given to secure
performance. Neither EOP nor any of the EOP Subsidiaries is in breach of any
provision of any agreement, document or contract governing its rights in or to
the interests owned or held by it, all of which agreements, documents and
contracts are (a) listed in Schedule 3.4(b) to the EOP Disclosure Letter (or
disclosed in the EOP SEC Documents (as defined herein)), (b) unmodified except
as described therein and (c) in full force and effect. To the Knowledge of EOP
(as defined herein), the other parties to any such agreement, document or
contract which is of a material nature are not in breach of any of their
respective obligations under such agreements, documents or contracts.

     3.5 Authority; Noncontravention; Consents.

     (a) EOP has the requisite power and authority to enter into this Agreement
and, subject to the requisite shareholder approval of the Merger (the "EOP
Shareholder Approvals" and, together with the Cornerstone Stockholder Approvals,
the "Shareholder Approvals"), to consummate the transactions contemplated by
this Agreement to which EOP is a party. The execution and delivery of this
Agreement by EOP and the consummation by EOP of the transactions contemplated by
this Agreement to which EOP is a party have been duly authorized by all
necessary action on the part of EOP, except for and subject to the EOP
Shareholder Approvals and the requisite approval, if any is required, of the
partners of EOP Partnership. This Agreement has been duly executed and delivered
by EOP and constitutes a valid and binding obligation of EOP, enforceable
against EOP in accordance with and subject to its terms, subject to applicable
bankruptcy, insolvency, moratorium or other similar laws relating to creditors'
rights and general principles of equity.

     (b) EOP Partnership has the requisite partnership power and, subject to the
requisite partner approval of the Partnership Merger (if any), authority to
enter into this Agreement and to consummate the transactions contemplated by
this Agreement to which EOP Partnership is a party. The execution and delivery
of this Agreement by EOP Partnership and the consummation by EOP Partnership of
the transactions contemplated by this Agreement to which EOP Partnership is a
party have been duly authorized by all necessary action on the part of EOP
Partnership, except for and subject to the EOP Partnership Approvals. This
Agreement has been duly executed and delivered by EOP Partnership and
constitutes a valid and binding obligation of EOP Partnership, enforceable
against EOP Partnership in accordance with and subject to its terms, subject to
applicable bankruptcy, insolvency, moratorium or other similar laws relating to
creditors' rights and general principles of equity.

     (c) Except as set forth in Schedule 3.5(c)(1) to the EOP Disclosure Letter,
the execution and delivery of this Agreement by EOP and EOP Partnership do not,
and the consummation of the transactions contemplated by this Agreement to which
EOP or EOP Partnership is a party and compliance by EOP or EOP Partnership with
the provisions of this Agreement will not, conflict with, or result in any
violation of or default (with or without notice or lapse of time, or both)
under, or give rise to a right of termination, cancellation or acceleration of
any material obligation or to loss of a material benefit under, or result in the
creation of any Lien upon any of the properties or assets of EOP or any EOP
Subsidiary under, (i) the EOP Declaration of Trust or the EOP Bylaws or the
comparable charter or organizational documents or partnership, operating or
similar agreement (as the case may be) of any other EOP Subsidiary, each as
amended or supplemented to the date of this Agreement, (ii) any loan or credit
agreement, note, bond, mortgage, indenture, reciprocal easement agreement, lease
or other agreement, instrument, permit, concession, franchise or license
applicable to EOP or any EOP Subsidiary or their respective properties or assets
or (iii) subject to the governmental filings and other matters referred to in
the following sentence, any Laws applicable to EOP or any EOP Subsidiary or
their respective properties or assets, other than, in the case of clause (ii) or
(iii), any such conflicts, violations, defaults, rights, loss or Liens that
individually or in the aggregate would not (x) reasonably be expected to have an
EOP Material Adverse Effect or (y) prevent the consummation of the transactions
contemplated by this
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Agreement. No consent, approval, order or authorization of, or registration,
declaration or filing with, any Governmental Entity is required by or with
respect to EOP or any EOP Subsidiary in connection with the execution and
delivery of this Agreement or the consummation by EOP of any of the transactions
contemplated by this Agreement, except for (i) the filing with the SEC of (x)
the Form S-4 (as defined herein) and (y) such reports under Section 13 (a) of
the Exchange Act as may be required in connection with this Agreement and the
transactions contemplated by this Agreement, (ii) the acceptance for record of
the Articles of Merger by the Department, (iii) the filing of the Certificate of
Merger with the Office of the Secretary of State of the State of Delaware, (iv)
such filings as may be required in connection with the payment of any transfer
and gains taxes and (v) such other consents, approvals, orders, authorizations,
registrations, declarations and filings (A) as are set forth in Schedule
3.5(c)(2) to the EOP Disclosure Letter or (B) as may be required under (x)
federal, state or local environmental laws or (y) the "blue sky" laws of various
states, to the extent applicable, or (C) which, if not obtained or made, would
not prevent or delay in any material respect the consummation of any of the
transactions contemplated by this Agreement or otherwise prevent EOP from
performing its obligations under this Agreement in any material respect or
reasonably be expected to have, individually or in the aggregate, an EOP
Material Adverse Effect.

     3.6 SEC Documents; Financial Statements; Undisclosed Liabilities. EOP and
EOP Partnership have filed all required reports, schedules, forms, statements
and other documents with the SEC since July 8, 1997 and November 19, 1997,
respectively, through the date hereof (the "EOP SEC Documents"). Schedule 3.6(a)
to the EOP Disclosure Letter contains a complete list of all EOP SEC Documents
filed by EOP and EOP Partnership with the SEC under the Exchange Act on or prior
to the date of this Agreement. All of the EOP SEC Documents (other than
preliminary material), as of their respective filing dates, complied in all
material respects with all applicable requirements of the Securities Act and the
Exchange Act and, in each case, the rules and regulations promulgated thereunder
applicable to such EOP SEC Documents. None of the EOP SEC Documents at the time
of filing contained any untrue statement of a material fact or omitted to state
any material fact required to be stated therein or necessary in order to make
the statements therein, in light of the circumstances under which they were
made, not misleading, except to the extent such statements have been modified or
superseded by later EOP SEC Documents filed and publicly available prior to the
date of this Agreement. The consolidated financial statements of EOP and the EOP
Subsidiaries included in the EOP SEC Documents complied as to form in all
material respects with applicable accounting requirements and the published
rules and regulations of the SEC with respect thereto, have been prepared in
accordance with GAAP (except, in the case of unaudited statements, as permitted
by the applicable rules and regulations of the SEC) applied on a consistent
basis during the periods involved (except as may be indicated in the notes
thereto) and fairly presented in all material respects, in accordance with the
applicable requirements of GAAP and the applicable rules and regulations of the
SEC, the consolidated financial position of EOP and the EOP Subsidiaries, taken
as a whole, as of the dates thereof and the consolidated results of operations
and cash flows for the periods then ended (subject, in the case of unaudited
statements, to normal year-end audit adjustments). Except for liabilities and
obligations set forth in the EOP SEC Documents or in Schedule 3.6(b) to the EOP
Disclosure Letter, neither EOP nor any EOP Subsidiary has any liabilities or
obligations of any nature (whether accrued, absolute, contingent or otherwise)
required by GAAP to be set forth on a consolidated balance sheet of EOP or in
the notes thereto and which, individually or in the aggregate, would reasonably
be expected to have an EOP Material Adverse Effect.

     3.7 Absence of Certain Changes or Events. Except as disclosed in the EOP
SEC Documents or in Schedule 3.7 to the EOP Disclosure Letter, since the date of
the most recent audited financial statements included in the EOP SEC Documents
(the "EOP Financial Statement Date"), EOP and the EOP Subsidiaries have
conducted their business only in the ordinary course (taking into account prior
practices, including the acquisition of properties and issuance of securities)
and there has not been (a) any material adverse change in the business,
financial condition or results of operations of EOP and the EOP Subsidiaries
taken as a whole (a "EOP Material Adverse Change"), nor has there been any
occurrence or circumstance that with the passage of time would reasonably be
expected to result in an EOP Material Adverse Change, (b) except for regular
quarterly distributions not in excess of $0.42 per EOP Common
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Share or EOP OP Unit or the stated distribution rate for each EOP Preferred
Share or EOP Preferred Unit, subject to rounding adjustments as necessary and
with customary record and payment dates, any authorization, declaration, setting
aside or payment of any dividend or other distribution (whether in cash, shares
or property) with respect to EOP Common Shares, EOP OP Units, EOP Preferred
Shares or EOP Preferred Units, (c) any split, combination or reclassification of
any of EOP's shares of beneficial interest, (d) any damage, destruction or loss,
whether or not covered by insurance, that has or would reasonably be expected to
have an EOP Material Adverse Effect or (e) any change made prior to the date of
this Agreement in accounting methods, principles or practices by EOP or any EOP
Subsidiary materially affecting its assets, liabilities or business, except
insofar as may have been disclosed in the EOP SEC Documents or required by a
change in GAAP.

     3.8 Litigation. Except as disclosed in the EOP SEC Documents or in Schedule
3.8 to the EOP Disclosure Letter, and other than personal injury and other
routine tort litigation arising from the ordinary course of operations of EOP
and the EOP Subsidiaries (a) which are covered by adequate insurance subject to
a reasonable deductible or retention limit or (b) for which all material costs
and liabilities arising therefrom are reimbursable pursuant to common area
maintenance or similar agreements, there is no suit, action or proceeding
pending (in which service of process has been received by an employee of EOP or
an EOP Subsidiary) or, to the Knowledge of EOP (as defined herein), threatened
in writing against or affecting EOP or any EOP Subsidiary that, individually or
in the aggregate, would reasonably be expected to (i) have an EOP Material
Adverse Effect or (ii) prevent the consummation of any of the transactions
contemplated by this Agreement, nor is there any judgment, decree, injunction,
rule or order of any Governmental Entity or arbitrator outstanding against EOP
or any EOP Subsidiary having, or which, insofar as reasonably can be foreseen,
in the future would have, any such effect.

     3.9 Properties.

     (a) Except as set forth in Schedule 3.9(a) to the EOP Disclosure Letter,
EOP or one of the EOP Subsidiaries owns fee simple title to each of the real
properties listed in the EOP SEC Filings as owned by it (the "EOP Properties"),
except where the failure to own such title would not have an EOP Material
Adverse Effect.

     (b) The EOP Properties are not subject to any Encumbrances or Property
Restrictions which reasonably could be expected to cause an EOP Material Adverse
Effect.

     (c) Valid policies of title insurance or fully-paid and enforceable
commitments therefor have been issued insuring EOP's or the applicable EOP
Subsidiary's fee simple title or leasehold estate, as the case may be, to the
EOP Properties in amounts which are, except in the case of San Felipe Plaza, at
least equal to the purchase price thereof paid by EOP or the applicable EOP
Subsidiaries therefor, except where the failure to obtain such title insurance
would not reasonably be expected to have an EOP Material Adverse Effect.

     (d) EOP has no Knowledge (i) that it has failed to obtain a certificate,
permit or license from any governmental authority having jurisdiction over any
of the EOP Properties where such failure would reasonably be expected to have an
EOP Material Adverse Effect or of any pending threat of modification or
cancellation of any of the same which would reasonably be expected to have an
EOP Material Adverse Effect, (ii) of any written notice of any violation of any
federal, state or municipal law, ordinance, order, rule, regulation or
requirement affecting any of the EOP Properties issued by any governmental
authorities which would reasonably be expected to have an EOP Material Adverse
Effect or (iii) of any structural defects relating to EOP Properties, EOP
Properties whose building systems are not in working order, physical damage to
any EOP Property for which there is no insurance in effect covering the cost of
restoration, any current renovation or uninsured restoration, except such
structural defects, building systems not in working order, physical damage,
renovation and restoration which, in the aggregate, would not reasonably be
expected to have an EOP Material Adverse Effect.

     (e) Except as set forth in Schedule 3.9(e) to the EOP Disclosure Letter,
neither EOP nor any of the EOP Subsidiaries has received any written or
published notice to the effect that (i) any condemnation or

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rezoning proceedings are pending or threatened with respect to any of the EOP
Properties or (ii) any zoning, building or similar law, code, ordinance, order
or regulation is or will be violated by the continued maintenance, operation or
use of any buildings or other improvements on any of the EOP Properties or by
the continued maintenance, operation or use of the parking areas, other than
such notices which, in the aggregate, would not reasonably be expected to have
an EOP Material Adverse Effect.

     (f) Except as set forth on Schedule 3.9(f) to the EOP Disclosure Letter,
all work to be performed, payments to be made and actions to be taken by EOP or
the EOP Subsidiaries prior to the date hereof pursuant to any agreement entered
into with a governmental body or authority in connection with a site approval,
zoning reclassification or similar action relating to any EOP Properties (e.g.,
Local Improvement District, Road Improvement District, Environmental
Mitigation), has been performed, paid or taken, as the case may be, except where
the failure to do so would, in the aggregate, not reasonably be expected to have
an EOP Material Adverse Effect, and EOP has no Knowledge of any planned or
proposed work, payments or actions that may be required after the date hereof
pursuant to such agreements.

     (g) The rent roll previously provided by EOP to Cornerstone (the "EOP Rent
Roll") lists each EOP Space Lease (as defined herein) in effect as of the
respective dates indicated in the EOP Rent Roll. "EOP Space Lease" means each
lease or other right of occupancy affecting or relating to a property in which
EOP Partnership (or an entity in which it directly or indirectly has an
interest) is the landlord, either pursuant to the terms of the lease agreement
or as successor to any prior landlord, but excluding any ground lease. EOP has
made available to Cornerstone true, correct and complete copies of all EOP Space
Leases, including all amendments, modifications, supplements, renewals,
extensions and guarantees related thereto, as of the date hereof. Except for
discrepancies that, either individually or in the aggregate, would not
reasonably be expected to have an EOP Material Adverse Effect, all information
set forth in the EOP Rent Roll is true, correct, and complete as of the date
thereof. Except as set forth in a delinquency report made available to
Cornerstone, neither EOP nor any EOP Subsidiary, on the one hand, nor, to the
Knowledge of EOP or EOP Partnership, any other party, on the other hand, is in
monetary default under any EOP Space Lease, except for such defaults that would
not reasonably be expected to have an EOP Material Adverse Effect.

     3.10 Environmental Matters.

     Except as disclosed in the EOP SEC Documents,

     (i) none of EOP, any of the EOP Subsidiaries or, to EOP's Knowledge, any
other Person has caused or permitted the presence of any Hazardous Materials at,
on or under any of the EOP Properties, such that the presence of such Hazardous
Materials (including the presence of asbestos in any buildings or improvements
at the EOP Properties) would, individually or in the aggregate, reasonably be
expected to have an EOP Material Adverse Effect;

     (ii) except in accordance with the Environmental Permits, there have been
no Releases of Hazardous Materials at, on, under or from (A) the EOP Properties,
or (B) any real property formerly owned, operated or leased by EOP or the EOP
Subsidiaries during the period of such ownership, operation or tenancy, which
would, individually or in the aggregate, reasonably be expected to have an EOP
Material Adverse Effect;

     (iii) EOP and the EOP Subsidiaries have not failed to comply in any
material respect with all Environmental Laws, and neither EOP nor any of the EOP
Subsidiaries has any liability under the Environmental Laws, except to the
extent such failure to comply or any such liability, individually or in the
aggregate, would not reasonably be expected to have an EOP Material Adverse
Effect; and

     (iv) EOP and the EOP Subsidiaries have been duly issued, and currently have
and will maintain through the Closing Date, all Environmental Permits except
where the failure to obtain and maintain such Environmental Permits would not
have a material adverse effect on the EOP Property necessary to operate their
businesses as currently operated. EOP and the EOP Subsidiaries have timely filed
applications for all Environmental Permits.

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     3.11 Taxes.

     (a) Each of EOP and the EOP Subsidiaries (i) has filed all Tax returns and
reports required to be filed by it (after giving effect to any filing extension
properly granted by a Governmental Entity having authority to do so), and all
such returns and reports are accurate and complete in all material respects,
(ii) has paid (or EOP has paid on its behalf) all Taxes shown on such returns
and reports as required to be paid by it and (iii) has complied in all material
respects with all applicable laws, rules and regulations relating to the payment
and withholding of Taxes (including, without limitation, withholding of Taxes
pursuant to Sections 1441, 1442, 1445, 3121, and 3402 of the Code or similar
provisions under any foreign laws) and has, within the time period prescribed by
law, withheld and paid over to the proper governmental entities all amounts
required to be so withheld and paid over under applicable laws and regulations,
except, with respect to all of the foregoing, where the failure to file such tax
returns or reports or failure to pay such Taxes or failure to comply with such
requirements would not reasonably be expected to have an EOP Material Adverse
Effect. The most recent audited financial statements contained in the EOP SEC
Documents reflect an adequate reserve for all material Taxes payable by EOP and
the EOP Subsidiaries for all taxable periods and portions thereof through the
date of such financial statements. Since the EOP Financial Statement Date, EOP
has incurred no liability for Taxes under Sections 857(b), 860(c) or 4981 of the
Code, including without limitation any Tax arising from a prohibited transaction
described in Section 857(b)(6) of the Code, and neither EOP nor any EOP
Subsidiary has incurred any material liability for Taxes other than in the
ordinary course of business. No event has occurred, and no condition or
circumstance exists, which presents a material risk that any material Tax
described in the preceding sentence will be imposed upon EOP or any EOP
Subsidiary. Neither EOP nor any EOP Subsidiary is the subject of any audit,
examination, or other proceeding in respect of federal income Taxes, and to
EOP's Knowledge, no audit, examination or other proceeding in respect of federal
income Taxes involving any of EOP or any EOP Subsidiary is being considered by
any Tax authority. To the Knowledge of EOP, no deficiencies for any Taxes have
been proposed, asserted or assessed against EOP or any of the EOP Subsidiaries,
and no requests for waivers of the time to assess any such Taxes are pending.

     (b) EOP (i) for all taxable years commencing with 1997, which is the first
year of EOP's existence for federal income tax purposes, through December 31,
1999, has been subject to taxation as a REIT within the meaning of Section 856
of the Code and has qualified as a REIT for all such years, (ii) has operated
since December 31, 1999 to the date of this representation, and intends to
continue to operate, in such a manner as to qualify as a REIT for the taxable
year that includes the Closing Date and (iii) has not taken or omitted to take
any action which would reasonably be expected to result in a challenge to its
status as a REIT and, to EOP's Knowledge, no such challenge is pending or
threatened. BeaMetFed, Inc. ("BeaMet") (i) for all taxable years commencing with
1997 through December 31, 1999 has been subject to taxation as a REIT within the
meaning of Section 856 of the Code and has qualified as a REIT for all such
years, (ii) has operated since December 31, 1999 to the date of this
representation, and intends to continue to operate, in such a manner as to
qualify as a REIT for the taxable year that includes the Closing Date and (iii)
has not taken or omitted to take any action which would reasonably be expected
to result in a challenge to its status as a REIT and, to EOP's Knowledge, no
such challenge is pending or threatened. Each EOP Subsidiary which is a
partnership, joint venture or limited liability company (i) has been treated
since its formation and continues to be treated for federal income tax purposes
as a partnership and not as a corporation or as an association taxable as a
corporation and (ii) has not since the later of its formation or the acquisition
by EOP of a direct or indirect interest therein, owned any assets (including,
without limitation, securities) that would cause EOP to violate Section
856(c)(4) of the Code. EOP Partnership is not a publicly-traded partnership
within the meaning of Section 7704(b) of the Code that is taxable as a
corporation pursuant to Section 7704(a) of the Code. Each EOP Subsidiary which
is a corporation has been since its formation a qualified REIT subsidiary under
Section 856(i) of the Code. Except as set forth in Schedule 3.11 to the EOP
Disclosure Letter, neither EOP nor any EOP Subsidiary holds any asset (x) the
disposition of which would be subject to rules similar to Section 1374 of the
Code as a result of an election under IRS Notice 88-19 or Temporary Treas. Reg.
sec.1.337(d)-5T or (y) which is subject to a consent filed pursuant to Section
341(f) of the Code and the regulations thereunder.
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     (c) To EOP's knowledge, as of the date hereof, EOP is a
"domestically-controlled REIT" within the meaning of Section 897(h)(4)(B) of the
Code.

     3.12 Brokers; Schedule of Fees and Expenses. No broker, investment banker,
financial advisor or other person, other than J.P. Morgan & Co. Incorporated,
the fees and expenses of which will be paid by EOP and are described in the
engagement letters between J.P. Morgan & Co. Incorporated and EOP, a true,
correct and complete copy of which has previously been given to Cornerstone, is
entitled to any broker's, finder's, financial advisor's or other similar fee or
commission in connection with the transactions contemplated hereby based upon
arrangements made by or on behalf of EOP or any EOP Subsidiary.

     3.13 Compliance with Laws. Neither EOP nor any of the EOP Subsidiaries has
violated or failed to comply with any statute, law, ordinance, regulation, rule,
judgment, decree or order of any Governmental Entity applicable to its business,
properties or operations, except to the extent that such violation or failure
would not reasonably be expected to have an EOP Material Adverse Effect.

     3.14 Contracts; Debt Instruments. Neither EOP nor any EOP Subsidiary has
received a written notice that EOP or any EOP Subsidiary is in violation of or
in default under (nor to the Knowledge of EOP does there exist any condition
which upon the passage of time or the giving of notice or both would cause such
a violation of or default under) any material loan or credit agreement, note,
bond, mortgage, indenture, lease, permit, concession, franchise, license or any
other material contract, agreement, arrangement or understanding, to which it is
a party or by which it or any of its properties or assets is bound, nor to the
Knowledge of EOP does such a violation or default exist, except to the extent
such violation or default, individually or in the aggregate, would not
reasonably be expected to have an EOP Material Adverse Effect, except as set
forth in the EOP SEC Documents or in Schedule 3.14 to the EOP Disclosure Letter.

     3.15 Opinion of Financial Advisor. EOP has received the opinion of J.P.
Morgan & Co. Incorporated, EOP's financial advisor, to the effect that the
consideration to be paid by EOP in connection with the Merger is fair, from a
financial point of view, to EOP.

     3.16 State Takeover Statutes. EOP has taken all action necessary to exempt
transactions between EOP and Cornerstone and its Affiliates from the operation
of Takeover Statutes.

     3.17 Investment Company Act of 1940. Neither EOP nor any of the EOP
Subsidiaries is, or at the Effective Time will be, required to be registered
under the 1940 Act.

     3.18 Definition of "Knowledge of EOP". As used in this Agreement, the
phrase "Knowledge of EOP" (or words of similar import) means the actual
knowledge of those individuals identified in Schedule 3.19 to the EOP Disclosure
Letter.

     3.19 Required Shareholder Approvals and Partner Approvals. The affirmative
vote of the holders of not less than a majority of all votes entitled to be cast
by holders of EOP Common Shares, and the affirmative vote of the partners of EOP
Partnership holding at least a majority of the outstanding EOP Partnership
interests (including partnership interests held by EOP), are the only votes of
the holders of any class or series of EOP capital shares necessary or required
under this Agreement or under applicable law to approve the Merger and this
Agreement. The approval of the Partnership Merger by EOP is the only vote
necessary or required under this Agreement or under applicable law to approve
the Partnership Merger and this Agreement.

                                   ARTICLE 4

                                   COVENANTS

     4.1 Conduct of Cornerstone's and Cornerstone Partnership's Business Pending
Merger. During the period from the date of this Agreement to the Effective
Times, except as consented to in writing by EOP or as expressly provided for in
this Agreement, Cornerstone and Cornerstone Partnership shall, and shall cause
(or, in the case of Cornerstone Subsidiaries and the Cornerstone Non-controlled
Subsidiary that

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Cornerstone or Cornerstone Partnership do not control, shall use commercially
reasonable efforts to cause) each of the Cornerstone Subsidiaries and
Cornerstone Non-controlled Subsidiary to:

     (a) conduct its business only in the usual, regular and ordinary course and
in substantially the same manner as heretofore conducted;

     (b) preserve intact its business organizations and goodwill and use
commercially reasonable efforts to keep available the services of its officers
and employees;

     (c) confer on a regular basis with one or more representatives of EOP to
report operational matters of materiality and, subject to Section 4.3, any
proposals to engage in material transactions;

     (d) promptly notify EOP of any material emergency or other material change
in the condition (financial or otherwise), business, properties, assets,
liabilities or the normal course of its businesses or in the operation of its
properties, or of any material governmental complaints, investigations or
hearings (or communications indicating that the same may be contemplated);

     (e) promptly deliver to EOP true and correct copies of any report,
statement or schedule filed with the SEC subsequent to the date of this
Agreement;

     (f) maintain its books and records in accordance with GAAP consistently
applied and not change in any material manner any of its methods, principles or
practices of accounting in effect at the Cornerstone Financial Statement Date,
except as may be required by the SEC, applicable law or GAAP;

     (g) duly and timely file all reports, tax returns and other documents
required to be filed with federal, state, local and other authorities, subject
to extensions permitted by law, provided Cornerstone notifies EOP that it is
availing itself of such extensions and provided such extensions do not adversely
affect Cornerstone's status as a qualified REIT under the Code;

     (h) not make or rescind any express or deemed election relative to Taxes
(unless required by law or necessary to preserve Cornerstone's status as a REIT
or the status of any Cornerstone Subsidiary as a partnership for federal income
tax purposes or as a qualified REIT subsidiary under Section 856(i) of the Code,
as the case may be);

     (i) not (A) acquire, enter into any option to acquire, or exercise an
option or other right or election or enter into any other commitment or
contractual obligation (each, a "Commitment") for the acquisition of any real
property or, except as permitted in a budget approved in writing by EOP, other
transaction (other than Commitments referred to in Schedule 4.1(i) to the
Cornerstone Disclosure Letter) involving in excess of $100,000, encumber assets
or commence construction of, or enter into any Commitment to develop or
construct other real estate projects, except in the ordinary course of its
office property business, including leasing activities pursuant to EOP-approved
guidelines (B) incur or enter into any Commitment to incur additional
indebtedness (secured or unsecured) except for working capital under its
revolving line(s) of credit and Commitments for indebtedness described on
Schedule 4.1(i) to the Cornerstone Disclosure Letter or (C) modify, amend or
terminate, or enter into any Commitment to modify, amend or terminate, any
indebtedness (secured or unsecured) in existence as of the date hereof;

     (j) not amend the Cornerstone Articles or the Cornerstone Bylaws, or the
articles or certificate of incorporation, bylaws, code of regulations,
partnership agreement, operating agreement or joint venture agreement or
comparable charter or organization document of any Cornerstone Subsidiary or
Cornerstone Non-controlled Subsidiary;

     (k) make no change in the number of shares of capital stock or units of
limited partnership interest issued and outstanding, other than pursuant to (i)
the exercise of options disclosed in Schedule 2.3 to the Cornerstone Disclosure
Letter, (ii) the conversion of the Cornerstone 7% Preferred Stock or the
Cornerstone Convertible Promissory Note if required by their terms, (iii) the
redemption of Cornerstone OP Units under existing contracts described on
Schedule 2.18, (iv) the redemption of Cornerstone OP Units pursuant to Section
1.1 of this Agreement, (v) the redemption of Cornerstone OP Units under the

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Cornerstone Partnership Agreement solely for shares of Cornerstone Common Stock,
or (vi) Cornerstone OP Units issuable upon the exercise of the First and Howard
option;

     (l) grant no options or other right or commitment relating to its shares of
capital stock or units of limited partnership interest or any security
convertible into its shares of capital stock or units of limited partnership
interest, or any security the value of which is measured by shares of beneficial
interest, or any security subordinated to the claim of its general creditors
and, other than or pursuant to Section 5.8(c) or (d) of this Agreement, not
amend or waive any rights under any of the Cornerstone Stock Options or
Cornerstone Stock Rights;

     (m) except as provided in Section 5.10 and in connection with the use of
Cornerstone Common Stock to pay the exercise price or tax withholding in
connection with equity-based employee benefit plans by the participants therein,
not (i) authorize, declare, set aside or pay any dividend or make any other
distribution or payment with respect to any Cornerstone Common Stock,
Cornerstone 7% Preferred Stock or Cornerstone OP Units or (ii) directly or
indirectly redeem, purchase or otherwise acquire any shares of capital stock or
units of partnership interest or any option, warrant or right to acquire, or
security convertible into, shares of capital stock or units of partnership
interest of Cornerstone, except for (A) deemed transfers of Cornerstone excess
shares required under Article 8 of the Cornerstone Articles in order to preserve
the status of Cornerstone as a REIT under the Code or Article 9 of the
Cornerstone Articles, and (B) redemptions of Cornerstone OP Units, whether or
not outstanding on the date of this Agreement, under the Cornerstone Partnership
Agreement in which solely Cornerstone Common Stock is utilized;

     (n) not sell, lease, mortgage, subject to Lien or otherwise dispose of any
of the Cornerstone Properties, except in connection with a transaction that is
permitted by Section 4.1(i), that is made in the ordinary course of business and
is the subject of a binding contract in existence on the date of this Agreement
and disclosed in Schedule 2.18 to the Cornerstone Disclosure Letter or in
connection with a transaction that is permitted by the leasing guidelines set
forth on Schedule 4.1(n) to the Cornerstone Disclosure Letter;

     (o) not sell, lease, mortgage, subject to Lien or otherwise dispose of any
of its personal property or intangible property, except in the ordinary course
of business and is not material, individually or in the aggregate;

     (p) not make any loans, advances or capital contributions to, or
investments in, any other Person, other than loans, advances and capital
contributions to Cornerstone Subsidiaries or the Cornerstone Non-controlled
Subsidiary in existence on the date hereof and ordinary course expense advances
to employees and except in connection with a transaction permitted by Section
4.1(i), and not enter into any new, or amend or supplement any existing,
contract, lease or other agreement with the Cornerstone Non-controlled
Subsidiary;

     (q) not pay, discharge or satisfy any claims, liabilities or obligations
(absolute, accrued, asserted or unasserted, contingent or otherwise), other than
the payment, discharge or satisfaction, in the ordinary course of business
consistent with past practice or in accordance with their terms, of liabilities
reflected or reserved against in, or contemplated by, the most recent
consolidated financial statements (or the notes thereto) furnished to EOP or
incurred in the ordinary course of business consistent with past practice;

     (r) not guarantee the indebtedness of another Person, enter into any "keep
well" or other agreement to maintain any financial statement condition of
another Person or enter into any arrangement having the economic effect of any
of the foregoing;

     (s) except as disclosed in Schedule 4.1(s) of the Cornerstone Disclosure
Letter, not enter into any Commitment with any officer, director or Affiliate of
Cornerstone or any of the Cornerstone Subsidiaries or the Cornerstone
Non-controlled Subsidiary or any material Commitment with any consultant;

     (t) except as disclosed in Schedule 4.1(t) of the Cornerstone Disclosure
Letter, not increase any compensation or enter into or amend any employment
agreement described in Schedule 2.18 to the

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Cornerstone Disclosure Letter with any of its officers, directors or employees
earning more than $100,000 per annum, other than as required by any contract or
Plan or in accordance with waivers by employees of benefits under such
agreements;

     (u) not adopt any new employee benefit plan or amend any existing plans or
rights;

     (v) not settle any stockholder derivative or class action claims arising
out of or in connection with any of the transactions contemplated by this
Agreement;

     (w) not change the ownership of any of its Subsidiaries or the Cornerstone
Non-controlled Subsidiary, except changes which arise as a result of the
acquisition of Cornerstone OP Units in exchange for Cornerstone Common Stock
pursuant to exercise of the Cornerstone OP Unit redemption right under Section
8.6 of the Cornerstone Partnership Agreement;

     (x) not accept a promissory note in payment of the exercise price payable
under any option to purchase shares of Cornerstone Common Stock;

     (y) not enter into any Tax Protection Agreement;

     (z) not settle or compromise any material federal, state, local or foreign
tax liability; and

     (aa) not authorize, recommend, propose or announce an intention to do any
of the foregoing prohibited actions, or enter into any contract, agreement,
commitment or arrangement to do any of the foregoing prohibited actions.

     4.2 Conduct of EOP's and EOP Partnership's Business Pending Merger.  During
the period from the date of this Agreement to the Effective Times, except as
consented to in writing by Cornerstone or as expressly provided for in this
Agreement, EOP and EOP Partnership shall, and shall cause (or, in the case of
Cornerstone Subsidiaries that Cornerstone or Cornerstone Partnership do not
control, shall use commercially reasonable efforts to cause) each of the EOP
Subsidiaries to:

     (a) preserve intact its business organizations and goodwill and use
commercially reasonable efforts to keep available the services of its officers
and employees;

     (b) confer on a regular basis with one or more representatives of
Cornerstone to report operational matters of materiality which would reasonably
be expected to have an EOP Material Adverse Effect;

     (c) promptly notify Cornerstone of any material emergency or other material
change in the condition (financial or otherwise), business, properties, assets,
liabilities, prospects or the normal course of its businesses or in the
operation of its properties, or of any material governmental complaints,
investigations or hearings (or communications indicating that the same may be
contemplated);

     (d) promptly deliver to Cornerstone true and correct copies of any report,
statement or schedule filed with the SEC subsequent to the date of this
Agreement;

     (e) maintain its books and records in accordance with GAAP consistently
applied and not change in any material manner any of its methods, principles or
practices of accounting in effect at the EOP Financial Statement Date, except as
may be required by the SEC, applicable law or GAAP;

     (f) duly and timely file all reports, tax returns and other documents
required to be filed with federal, state, local and other authorities, subject
to extensions permitted by law, provided such extensions do not adversely affect
EOP's status as a qualified REIT under the Code;

     (g) not make or rescind any express or deemed election relative to Taxes
(unless required by law or necessary to preserve EOP's status as a REIT or the
status of any EOP Subsidiary as a partnership for federal income tax purposes or
as a qualified REIT subsidiary under Section 856(i) of the Code, as the case may
be);

     (h) not amend the EOP Declaration of Trust, the EOP Bylaws or the EOP
Partnership Agreement (except for the Proposed EOP Charter Relating to Voting
Requirements, the Proposed EOP Charter Amendment Relating to Domestically
Controlled REIT Status (as defined herein), the proposed

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<PAGE>   271

amendment to Section 7.4 of the EOP Partnership Agreement, the amendments to the
EOP Partnership Agreement described in Section 5.4(c), the filing of Articles
Supplementary to elect to be subject to the provisions of Section 3-804(c) of
the Maryland General Corporation Law and to the extent necessary to reflect the
admission of additional limited partners and other amendments in connection
therewith that can be made by EOP without a vote of limited partners and that
will not, individually or in the aggregate, materially adversely affect the
rights or obligations of holders of EOP OP Units); as used herein, (i) "Proposed
EOP Charter Amendment Relating to Certain Voting Requirements" means the
proposed amendment to EOP's Declaration of Trust, substantially the form
attached hereto as Exhibit D, which has been approved by the Board of Trustees
of EOP and is proposed to be submitted to a vote of the shareholders of EOP,
(ii) "Proposed EOP Charter Amendment Relating to Domestically Controlled REIT
Status" means the proposed amendment to EOP's Declaration of Trust,
substantially the form attached hereto as Exhibit E, which has been approved by
the Board of Trustees of EOP and is proposed to be submitted to a vote of the
shareholders of EOP at the EOP Shareholders Meeting (as defined below) and (iii)
"Proposed EOP Charter Amendments" means, collectively, the Proposed EOP Charter
Relating to Voting Requirements and the Proposed EOP Charter Amendment Relating
to Domestically Controlled REIT Status;

     (i) except as provided in Section 5.10 hereof and in connection with the
use of EOP Common Shares to pay the exercise price or tax withholding in
connection with equity-based employee benefit plans by the participants therein,
not (i) authorize, declare, set aside or pay any dividend or make any other
distribution or payment with respect to any EOP Common Shares or EOP OP Units or
(ii) directly or indirectly redeem, purchase or otherwise acquire any shares of
capital stock, membership interests or units of partnership interest or any
option, warrant or right to acquire, or security convertible into, shares of
capital stock, membership interests, or units of partnership interest of EOP,
except for (A) redemptions of EOP Common Shares required under Section 7.3.6 of
the EOP Declaration of Trust in order to preserve the status of EOP as a REIT
under the Code, (B) redemptions of EOP OP Units, whether or not outstanding on
the date of this Agreement, under the EOP Partnership Agreement in which EOP
Common Shares are utilized, and (C) repurchases of EOP Common Shares pursuant to
its publicly announced share repurchase program;

     (j) not (A) enter into or agree to effect any merger, acquisition,
consolidation, reorganization or other business combination with any third party
in which EOP is not the surviving party thereto or (B) enter into or agree to
effect any merger, acquisition, exchange offer or other business combination
with a third party in which EOP is the surviving party that would result in the
issuance of equity securities representing in excess of 20% of the outstanding
EOP Common Shares on the date any such business combination is entered into or
agreed to unless, in either such case, such business combination is approved by
Cornerstone, which approval shall not be unreasonably withheld or delayed, or
the business combination agreement provides that the required vote of EOP
shareholders for approval of such business combination is no less than the
affirmative vote of holders of EOP Common Shares representing more than 50% of
the sum of (x) the number of EOP Common Shares outstanding at the time of such
approval plus (y) 50,000,000; and

     (k) not authorize, recommend, propose or announce an intention to do any of
the foregoing prohibited actions, or enter into any contract, agreement,
commitment or arrangement to do any of the foregoing prohibited actions.

     4.3 No Solicitation.

     (a) Prior to the Effective Time of the Merger, Cornerstone agrees, for
itself and in its capacity as the sole general partner of the Cornerstone
Partnership, that:

          (i) none of it, Cornerstone Partnership, any Cornerstone Subsidiary or
     the Cornerstone Non-controlled Subsidiary shall invite, initiate, solicit
     or encourage, directly or indirectly, any inquiries, proposals, discussions
     or negotiations or the making or implementation of any proposal or offer
     (including, without limitation, any proposal or offer to its stockholders)
     with respect to a merger, acquisition, tender offer, exchange offer,
     transaction resulting in the issuance of securities representing 10% or
     more of the outstanding equity securities of Cornerstone or Cornerstone
     Partnership,
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     consolidation, business combination, recapitalization, liquidation,
     dissolution, share exchange, business combination, sale, lease, exchange,
     mortgage, pledge, transfer or other disposition of 10% or more of the
     assets or equity securities (including, without limitation, partnership
     interests and units) of Cornerstone or Cornerstone Partnership, other than
     the Mergers (any such proposal or offer being hereinafter referred to as an
     "Acquisition Proposal"), or engage in any discussions or negotiations with
     or provide any confidential or non-public information or data to, any
     person relating to, or that may reasonably be expected to lead to, an
     Acquisition Proposal, or enter into any letter of intent, agreement in
     principle or agreement relating to an Acquisition Proposal, or propose
     publicly to agree to do any of the foregoing, or otherwise facilitate any
     effort or attempt to make or implement an Acquisition Proposal;

          (ii) none of it, Cornerstone Partnership, any Cornerstone Subsidiary
     or the Cornerstone Non-controlled Subsidiary will permit any officer,
     director, employee, affiliate, agent, investment banker, financial advisor,
     attorney, accountant, broker, finder, consultant or other agent or
     representative of Cornerstone to engage in any of the activities described
     in Section 4.3(a);

          (iii) it, Cornerstone Partnership and the Cornerstone Subsidiaries and
     Cornerstone Non-controlled Subsidiary will immediately cease and cause to
     be terminated any existing activities, discussions or negotiations with any
     parties conducted heretofore with respect to any of the foregoing and will
     take the necessary steps to inform the individuals or entities referred to
     in Section 4.3(b) of the obligations undertaken in this Section 4.3; and

          (iv) it will notify EOP promptly (but in any event within 24 hours) if
     Cornerstone, Cornerstone Partnership, any Cornerstone Subsidiary, the
     Cornerstone Non-controlled Subsidiary or any individual or entity referred
     to in Section 4.3(b) receives any such inquiries or proposals, or any
     requests for such information, or if any such negotiations or discussions
     are sought to be initiated or continued with it, and include in such notice
     the identity of the Person making such inquiry, proposal or request, the
     material terms of such inquiry, proposal or request and, if in writing,
     shall promptly deliver to EOP a copy of such inquiry, proposal or request
     along with all other related documentation and correspondence;

     (b) Notwithstanding Section 4.3(a), the Board of Directors of Cornerstone
(including with respect to Cornerstone's capacity as the sole general partner of
Cornerstone Partnership) shall not be prohibited from furnishing information to
or entering into discussions or negotiations with, any person or entity that
makes an unsolicited bona fide written Acquisition Proposal, if, and only to the
extent that (i) a majority of the Board of Directors of Cornerstone determines
in good faith, after consultation with its outside counsel, that such action is
required for the Board of Directors of Cornerstone to comply with its fiduciary
duties to stockholders imposed by applicable law, (ii) prior to furnishing such
information to, or entering into discussions or negotiations with, such person
or entity, Cornerstone provides written notice to EOP to the effect that it is
furnishing information to, or entering into discussions with such person or
entity and (iii) Cornerstone enters into a confidentiality agreement with such
Person on terms in the aggregate not more favorable to such Person than the
terms of the Confidentiality Agreement.

     (c) Notwithstanding anything to the contrary set forth in Section 4.3(a) or
4.3(b), in the event that an Acquisition Proposal constitutes a Superior
Acquisition Proposal (as defined herein), nothing contained in this Section 4.3
shall prohibit the Board of Directors of Cornerstone from withdrawing,
modifying, amending or qualifying its recommendation of this Agreement and the
Merger as required under Section 5.1(d) hereof and recommending such Superior
Acquisition Proposal to its stockholders: (i) if but only if, Cornerstone: (A)
complies fully with this Section 4.3 and (B) provides EOP with at least three
(3) business days' prior written notice of its intent to withdraw, modify, amend
or qualify its recommendation of this Merger Agreement and the Merger, (ii) if,
in the event that during such three (3) business days EOP makes a counter
proposal to such Superior Acquisition Proposal (any such counter proposal being
referred to in this Agreement as the "EOP Counter Proposal"), Cornerstone's
Board of Directors in good faith, taking into account the advice of its outside
financial advisors of nationally recognized reputation, determines (A) that the
EOP Counter Proposal is not at least as favorable to Cornerstone's stockholders
as the Superior Acquisition Proposal, from a financial point of view, and

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(B) the EOP Counter Proposal is not at least as favorable generally to
Cornerstone's stockholders (taking into account all financial and strategic
considerations and other relevant factors, including relevant legal, financial,
regulatory and other aspects of such proposals, and the conditions, prospects
and time required for completion of such proposal), and (iii) Cornerstone shall
have terminated this Agreement in accordance with Section 7.1(h).

     (d) For all purposes of this Agreement, "Superior Acquisition Proposal"
means a bona fide written proposal made by a third party to acquire, directly or
indirectly, Cornerstone and/or Cornerstone Partnership pursuant to a tender or
exchange offer, merger, share exchange, consolidation or sale of all or
substantially all of the assets of Cornerstone, Cornerstone Partnership, and the
Cornerstone Subsidiaries or otherwise (i) on terms which a majority of the Board
of Directors of Cornerstone determines in good faith, (A) taking into account
the advice of Cornerstone's financial advisors of nationally recognized
reputation, are superior, from a financial point of view, to Cornerstone's
stockholders to those provided for in the Merger and (B) to be more favorable
generally to Cornerstone's stockholders (taking into account all financial and
strategic considerations and other relevant factors, including relevant legal,
financial, regulatory and other aspects of such proposals, and the conditions,
prospects and time required for completion of such proposal), (ii) for which
financing, to the extent required, is then fully committed and capable of being
obtained and (iii) which the Board of Directors of Cornerstone determines in
good faith is reasonably capable of being consummated.

     (e) Any disclosure that the Board of Directors of Cornerstone may be
compelled to make with respect to the receipt of an Acquisition Proposal in
order to comply with its duties to shareholders imposed by applicable law or
Rule 14d-9 or 14e-2 of the Exchange Act will not constitute a violation of this
Section 4.3.

     (f) Nothing in this Section 4.3 shall (i) permit Cornerstone to terminate
this Agreement (except as expressly provided in Article 7) or (ii) affect any
other obligations of Cornerstone under this Agreement.

     4.4 Affiliates. Prior to the Effective Time of the Merger, Cornerstone
shall cause to be prepared and delivered to EOP a list (reasonably satisfactory
to counsel for EOP) identifying all persons who, at the time of the Cornerstone
Stockholders Meeting and the EOP Shareholders Meeting, may be deemed to be
"affiliates" of Cornerstone or Cornerstone Partnership as that term is used in
paragraphs (c) and (d) of Rule 145 under the Securities Act (the "Rule 145
Affiliates"). Cornerstone shall use its commercially reasonable efforts to cause
each person who is identified as a Rule 145 Affiliate in such list to deliver to
EOP on or prior to the Effective Time a written agreement, in the form
previously approved by the parties hereto, that such Rule 145 Affiliate will not
sell, pledge, transfer or otherwise dispose of any EOP Common Shares and EOP OP
Units issued to such Rule 145 Affiliate pursuant to the Merger, except pursuant
to an effective registration statement under the Securities Act or in compliance
with paragraph (d) of Rule 145 or as otherwise permitted by the Securities Act.
EOP shall be entitled to place legends as specified in such written agreements
on the certificates representing any EOP Common Shares to be received pursuant
to the terms of this Agreement by such Rule 145 Affiliates who have executed
such agreements and to issue appropriate stop transfer instructions to the
transfer agent for the EOP Common Shares and EOP OP Units issued to such Rule
145 Affiliates, consistent with the terms of such agreements. EOP and EOP OP
shall timely file the reports required to be filed by it under the Exchange Act
and the rules and regulations adopted by the SEC thereunder, and it will take
such further action as any Rule 145 Affiliate of Cornerstone or EOP may
reasonably request, all to the extent required from time to time to enable such
Rule 145 Affiliate to sell shares of beneficial interest of EOP received by such
Rule 145 Affiliate in the Merger without registration under the Securities Act
pursuant to (i) Rule 145(d)(1) under the Securities Act, as such rule may be
amended from to time, or (ii) any successor rule or regulation hereafter adopted
by the SEC.

     4.5 Other Actions. Each of Cornerstone and Cornerstone Partnership, on the
one hand, and EOP and EOP Partnership, on the other hand, shall not take, and
shall use commercially reasonable efforts to cause their respective Subsidiaries
not to take, any action that would result in (i) any of the representations and
warranties of such party (without giving effect to any "knowledge"
qualification) set forth in this Agreement that are qualified as to materiality
becoming untrue, (ii) any of such representations and

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warranties (without giving effect to any "knowledge" qualification) that are not
so qualified becoming untrue in any material respect or (iii) except as
contemplated by Section 4.3, any of the conditions to the Merger set forth in
Article 6 not being satisfied.

                                   ARTICLE 5

                              ADDITIONAL COVENANTS

     5.1 Preparation of the Form S-4 and the Proxy Statement; Cornerstone
Stockholders Meeting, Cornerstone Unitholders Consent Solicitation and EOP
Shareholders Meeting.

     (a) As promptly as practicable after execution of this Agreement, (i) each
of Cornerstone and EOP shall prepare and file with the SEC (with appropriate
requests for confidential treatment, unless the parties hereto otherwise agree)
under the Exchange Act, one or more joint proxy statements/prospectuses, forms
of proxies and information statements (such joint proxy statement(s)
/prospectus(es) and information statements together with any amendments to
supplements thereto, the "Joint Proxy Statement") relating to the stockholder
meeting of Cornerstone and the shareholder meeting of EOP, the vote of the
stockholders of Cornerstone with respect to this Agreement and the shareholders
of EOP with respect to the Merger and the Proposed EOP Charter Amendment
Relating to Domestically Controlled REIT Status, and the consent, if any, of
partners of Cornerstone Partnership and EOP Partnership in connection with any
required Partner Approvals and (ii) in connection with the clearance by the SEC
of the Joint Proxy Statement, EOP and Cornerstone, if applicable, shall prepare
and file with the SEC under the Securities Act one or more registration
statements on Form S-4 (such registration statements, together with any
amendments or supplements thereto, the "Form S-4"), in which the Joint Proxy
Statement will be included, as one or more prospectuses in connection with the
registration under the Securities Act of the EOP Common Shares and EOP OP Units
to be distributed to the holders of Cornerstone Common Stock and Cornerstone OP
Units in the Mergers. The respective parties will cause the Proxy Statement and
the Form S-4 to comply as to form in all material respects with the applicable
provisions of the Securities Act, the Exchange Act and the rules and regulations
thereunder. Each of Cornerstone, Cornerstone Partnership, EOP and EOP
Partnership shall furnish all information about itself and its business and
operations and all necessary financial information to the other as the other may
reasonably request in connection with the preparation of the Joint Proxy
Statement and the Form S-4. EOP and Cornerstone, if applicable, shall use its
commercially reasonable efforts, and Cornerstone will cooperate with it, to have
the Form S-4 declared effective by the SEC as promptly as practicable (including
clearing the Proxy Statement with the SEC. Each of Cornerstone and Cornerstone
Partnership, on the one hand, and EOP and EOP Partnership, on the other hand,
agree promptly to correct any information provided by it for use in the Joint
Proxy Statement and the Form S-4 if and to the extent that such information
shall have become false or misleading in any material respect, and each of the
parties hereto further agrees to take all steps necessary to amend or supplement
the Joint Proxy Statement and the Form S-4 and to cause the Joint Proxy
Statement and the Form S-4 as amended or supplemented to be filed with the SEC
and to be disseminated to their respective stockholders and shareholders and
partners, in each case as and to the extent required by applicable federal and
state securities laws. Each of Cornerstone, Cornerstone Partnership, EOP and EOP
Partnership agrees that the information provided by it for inclusion in the
Joint Proxy Statement or the Form S-4 and each amendment or supplement thereto,
at the time of mailing thereof and at the time of the respective meetings of
stockholders and shareholders of Cornerstone and EOP and at the time of the
respective taking of consents, if any, of partners of Cornerstone Partnership
and EOP Partnership, will not include an untrue statement of a material fact or
omit to state a material fact required to be stated therein or necessary to make
the statements therein, in light of the circumstances under which they were
made, not misleading. EOP will advise and deliver copies (if any) to
Cornerstone, promptly after it receives notice thereof, of any request by the
SEC for amendment of the Joint Proxy Statement or the Form S-4 or comments
thereon and responses thereto or requests by the SEC for additional information
(regardless of whether such requests relate to EOP or EOP Partnership, on the
one hand, and Cornerstone or Cornerstone Partnership, on the other hand), and
EOP shall promptly notify Cornerstone, and Cornerstone shall promptly notify
EOP, if applicable, of (i) the time

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<PAGE>   275

when the Form S-4 has become effective, (ii) the filing of any supplement or
amendment thereto, (iii) the issuance of any stop order, and (iv) the suspension
of the qualification and registration of the EOP Common Shares and EOP OP Units
issuable in connection with the Mergers.

     (b) Each of Cornerstone, Cornerstone Partnership, EOP and EOP Partnership
shall use its commercially reasonable efforts to timely mail the joint proxy
statement/prospectus contained in the Form S-4 to its stockholders or
shareholders. It shall be a condition to the mailing of the joint proxy
statement/prospectus that (i) EOP and EOP Partnership shall have received a
"comfort" letter from PricewaterhouseCoopers LLP, independent public accountants
for Cornerstone and Cornerstone Partnership, of the kind contemplated by the
Statement of Auditing Standards with respect to Letters to Underwriters
promulgated by the American Institute of Certified Public Accountants (the
"AICPA Statement"), dated as of the date on which the Form S-4 shall become
effective and as of the Effective Time, addressed to EOP and EOP Partnership, in
form and substance reasonably satisfactory to EOP and EOP Partnership,
concerning the procedures undertaken by PricewaterhouseCoopers LLP with respect
to the financial statements and information of Cornerstone and Cornerstone
Partnership and their subsidiaries and the Cornerstone Non-controlled Subsidiary
contained in the Form S-4 and the other matters contemplated by the AICPA
Statement and otherwise customary in scope and substance for letters delivered
by independent public accountants in connection with transactions such as those
contemplated by this Agreement and (ii) Cornerstone shall have received a
"comfort" letter from Ernst & Young LLP, independent public accountants for EOP
and EOP Partnership, of the kind contemplated by the AICPA Statement, dated as
of the date on which the Form S-4 shall become effective and as of the Effective
Time, addressed to Cornerstone and Cornerstone Partnership, in form and
substance reasonably satisfactory to Cornerstone, concerning the procedures
undertaken by Ernst & Young LLP with respect to the financial statements and
information of EOP, EOP Partnership and their subsidiaries contained in the Form
S-4 and the other matters contemplated by the AICPA Statement and otherwise
customary in scope and substance for letters delivered by independent public
accountants in connection with transactions such as those contemplated by this
Agreement.

     (c) EOP will duly call and give notice of and, as soon as practicable
following the date of this Agreement (but in no event sooner than 20 business
days following the date the Joint Proxy Statement is mailed to the shareholders
of EOP), convene and hold a meeting of its shareholders (the "EOP Shareholders
Meeting") for the purpose of obtaining the EOP Shareholder Approvals. EOP shall,
through its Board of Trustees, recommend to its shareholders approval of this
Agreement, the Merger and the transactions contemplated by this Agreement.

     (d) Cornerstone will duly call and give notice of and, as soon as
practicable following the date of this Agreement (but in no event sooner than 20
business days following the date the Joint Proxy Statement is mailed to the
stockholders of Cornerstone), convene and hold a meeting of its stockholders
(the "Cornerstone Stockholders Meeting") for the purpose of obtaining the
Cornerstone Stockholder Approvals. Cornerstone shall, through its Board of
Directors, recommend to its stockholders approval of this Agreement, the Merger
and the transactions contemplated by this Agreement and include such
recommendation in the Proxy Statement; provided, however, that prior to the
Cornerstone Stockholders Meeting, such recommendation may be withdrawn,
modified, amended or qualified if and only to the extent permitted by Section
4.3(c) hereof.

     (e) EOP and Cornerstone shall use their commercially reasonable efforts to
convene their respective shareholder and stockholder meetings on the same day,
which day, subject to the provisions of Sections 5.1(c), 5.1(d) and 5.3, shall
be a day not later than 60 days after the date the Joint Proxy Statement is
mailed.

     (f) If on the date for the EOP Shareholders Meeting and Cornerstone
Stockholders Meeting established pursuant to Section 5.1(e) of this Agreement,
either EOP or Cornerstone has not received duly executed proxies for a
sufficient number of votes to approve the Merger, then both parties shall
recommend the adjournment of their respective shareholders and stockholders
meetings until one or more dates not later than the date 10 days after the
originally scheduled date of the shareholders meetings.

                                      A-41
<PAGE>   276

     (g) Cornerstone shall request written consents for approval by the limited
partners of Cornerstone Partnership of each of the matters described in the
definition of Cornerstone Partner Approvals. Cornerstone hereby agrees to vote
in favor of or consent to, as applicable, the Partnership Merger, to the extent
approval thereof is required by the Cornerstone Partnership Agreement.
Cornerstone shall recommend to the limited partners of Cornerstone Partnership
that they approve such matters. EOP shall request written consents, if any is
required, by the limited partners, of EOP Partnership of each of the matters
described in the definition of EOP Partner Approvals. EOP hereby agrees to vote,
if any is required, in favor of such matters and to recommend to the limited
partners of EOP Partnership that they approve such matters.

     5.2 Access to Information; Confidentiality. Subject to the requirements of
confidentiality agreements with third parties in existence on the date hereof,
each of the parties shall, and shall cause each of its Subsidiaries (and, in the
case of Cornerstone, the Cornerstone Non-controlled Subsidiary) to, afford to
the other parties and to the officers, employees, accountants, counsel,
financial advisors and other representatives of such other parties, reasonable
access during normal business hours prior to the Effective Time to all their
respective properties, books, contracts, commitments, personnel and records and,
during such period, each of the parties shall, and shall cause each of its
Subsidiaries (and, in the case of Cornerstone, the Cornerstone Non-controlled
Subsidiary) to, furnish promptly to the other parties (a) a copy of each report,
schedule, registration statement and other document filed by it during such
period pursuant to the requirements of federal or state securities laws and (b)
all other information concerning its business, properties and personnel as such
other party may reasonably request. Each of the parties shall, and shall cause
its Subsidiaries (and in the case of Cornerstone, the Cornerstone Non-controlled
Subsidiary) to, use commercially reasonable efforts to cause its officers,
employees, accountants, counsel, financial advisors and other representatives
and affiliates to, hold any nonpublic information in confidence in accordance
with the Confidentiality Agreement, which shall remain in full force and effect
pursuant to the terms thereof, notwithstanding the execution and delivery of
this Agreement or the termination hereof.

     5.3 Commercially Reasonable Efforts; Notification.

     (a) Subject to the terms and conditions herein provided, each of the
parties shall: (i) use commercially reasonable efforts to cooperate with one
another in (A) determining which filings are required to be made prior to the
Effective Time with, and which consents, approvals, permits or authorizations
are required to be obtained prior to the Effective Time from, governmental or
regulatory authorities of the United States, the several states and foreign
jurisdictions and any third parties in connection with the execution and
delivery of this Agreement, and the consummation of the transactions
contemplated hereby, including, without limitation, any filing under the HSR
Act, and (B) timely making all such filings and timely seeking all such
consents, approvals, permits and authorizations; (ii) use commercially
reasonable efforts (other than the payment of money which is not contractually
required to be paid) to obtain in writing any consents required from third
parties to effectuate the Mergers, such consents to be in form reasonably
satisfactory to each of the parties (including, without limitation, taking the
actions contemplated under Schedule 5.3(a)(ii)); and (iii) use commercially
reasonable efforts to take, or cause to be taken, all other action and do, or
cause to be done, all other things necessary, proper or appropriate to
consummate and make effective the transactions contemplated by this Agreement.
If at any time after the Effective Time any further action is necessary or
desirable to carry out the purpose of this Agreement, each party shall take all
such necessary action.

     (b) Cornerstone and Cornerstone Partnership shall use commercially
reasonable efforts to obtain from PricewaterhouseCoopers LLP access to all work
papers relating to audits of Cornerstone and Cornerstone Partnership performed
by PricewaterhouseCoopers LLP, and the continued cooperation of
PricewaterhouseCoopers LLP with regard to the preparation of consolidated
financial statements for the Surviving Trust.

     (c) Cornerstone and Cornerstone Partnership shall give prompt notice to EOP
and EOP Partnership, and EOP and EOP Partnership shall give prompt notice to
Cornerstone and Cornerstone Partnership, (i) if any representation or warranty
made by it contained in this Agreement that is qualified as to

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materiality becomes untrue or inaccurate in any respect or any such
representation or warranty that is not so qualified becomes untrue or inaccurate
in any material respect or (ii) of the failure by it to comply with or satisfy
in any material respect any covenant, condition or agreement to be complied with
or satisfied by it under this Agreement; provided, however, that no such
notification shall affect the representations, warranties, covenants or
agreements of the parties or the conditions to the obligations of the parties
under this Agreement.

     5.4 Tax Matters.

     (a) Each of EOP and Cornerstone shall use its commercially reasonable
efforts before and after the Effective Time to cause the Merger to qualify as a
reorganization under the provisions of Sections 368(a) of the Code and to obtain
the opinions of counsel referred to in Sections 6.2(e) and 6.3(e).

     (b) Unless, and only to the extent, expressly provided otherwise in the Tax
Protection Agreements described in Schedule 2.18(j) to the Cornerstone
Disclosure Letter to be assumed by EOP pursuant to Section 5.14, EOP Partnership
and its Subsidiaries shall use the "traditional method" under Treasury
Regulations Section 1.704-3(b) for purposes of making allocations under Section
704(c) of the Code with respect to the properties of Cornerstone Partnership and
its Subsidiaries acquired in the Partnership Merger to take into account
differences as of the Effective Time of the Partnership Merger between the
adjusted tax bases of such properties and their respective fair market values
(referred to as the "Section 704(c) values"), with no curative allocations to
offset the effect of the "ceiling rule." EOP Partnership and Cornerstone
Partnership shall negotiate in good faith to agree upon the "Section 704(c)
values" of the properties of Cornerstone Partnership and its Subsidiaries as of
the Effective Time of the Partnership Merger. Unless, and only to the extent,
expressly provided otherwise in the Tax Protection Agreements described in
Schedule 2.18(j) to the Cornerstone Disclosure Letter to be assumed by EOP
pursuant to Section 5.14, EOP Partnership and its Subsidiaries shall determine
in their reasonable discretion the method to be used for allocating "excess
nonrecourse liabilities" of EOP Partnership pursuant to Treasury Regulations
Section 1.752-3(a)(3) following the Closing Date, provided that (i) EOP
Partnership shall not use with respect to the former limited partners in
Cornerstone Partnership a method that is less favorable than the method used by
EOP Partnership with respect to the other limited partners of EOP Partnership
who are not parties to an express agreement specifying a particular method to be
used for such purposes, and (ii) in the case of a Cornerstone Partner who, prior
to the Partnership Merger, had been specially allocated a portion of a
Cornerstone Partnership nonrecourse liability secured by a property with respect
to which such Cornerstone Partner has a built-in gain under Section 704(c) of
the Code to take into account such Cornerstone Partner's share of such built-in
gain that was not taken into account in making the allocation of such liability
under Treasury Regulation Section 1.752-3(a)(2), EOP Partnership shall continue
such method of allocating such liability following the Merger.

     (c) EOP Partnership shall amend the EOP Partnership Agreement at or prior
to the Effective Time of the Partnership Merger to incorporate provisions
relating to the restoration of deficit capital accounts that will permit each
limited partner of Cornerstone Partnership who has entered into an agreement
with Cornerstone Partnership prior to the Partnership Merger relating to the
restoration of deficit capital accounts to continue to be obligated to restore
any deficit in its capital account in EOP Partnership in an amount that is not
less than the maximum potential amount that such limited partner was obligated
to restore to Cornerstone Partnership immediately prior to the Effective Time of
the Partnership Merger. Such deficit capital account restoration provisions to
be incorporated in the EOP Partnership Agreement shall be in substantially the
form of the deficit capital account restoration provisions incorporated in the
Cornerstone Partnership Agreement pursuant to the Fourth Amendment of Agreement
of Limited Partnership of Cornerstone Properties Limited Partnership, with such
changes thereto as shall be approved by Cornerstone Partnership, provided,
however, that except as set forth in the next sentence below or in the Tax
Protection Agreements listed on Schedule 2.18(j) to the Cornerstone Disclosure
Letter, no Cornerstone Partner shall have the right to increase the amount of
its deficit restoration obligation following the Partnership Merger to an amount
in excess of the maximum potential amount that such limited partner was
obligated to restore to Cornerstone Partnership immediately prior to the
Effective Time of the Partnership Merger. Notwithstanding the proviso in the
immediately preceding sentence, the
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Cornerstone Partners as a group shall have the right, at any time following the
Merger and without the consent of EOP, to increase their maximum potential
deficit restoration obligations as a group (as determined immediately prior to
the Merger) by an aggregate amount of up to $50 million, reduced by the amount
of any increase therein that shall occur under the Cornerstone Partnership
Agreement during the period commencing on the date hereof and ending immediately
prior to the Effective Time of the Partnership Merger. Any election to increase
or to take on a deficit restoration obligation election permitted under a Tax
Protection Agreement listed on Schedule 2.18(j) to the Cornerstone Disclosure
Letter shall not be taken into account in applying the foregoing $50 million
limitation. Notwithstanding any the foregoing, EOP Partnership shall not be
obligated to maintain any level of partnership recourse debt in excess of the
amounts otherwise specifically required to be maintained under the Tax
Protection Agreements listed on Schedule 2.18(j) to the Cornerstone Disclosure
Letter. In addition, the amendment to the EOP Partnership Agreement will contain
a provision to the effect that (i) EOP Partnership will consider in good faith a
request from a former Cornerstone Partner to increase the amount of its deficit
restoration obligation from time to time after the Partnership Merger if the
former Cornerstone Partner shall provide information from its professional tax
advisor satisfactory to EOP Partnership showing that, in the absence of such an
increase, such former Cornerstone Partner would not likely be allocated from EOP
Partnership sufficient indebtedness under Section 752 of the Code and the
at-risk provisions under Section 465 of the Code to avoid the recognition of
gain (other than gain required to be recognized by reason of actual cash
distributions from EOP Partnership following the Partnership Merger); (ii) EOP
Partnership and its professional tax advisors will cooperate in good faith with
the former Cornerstone Partner and its professional tax advisor to provide such
information regarding the allocation of the EOP Partnership liabilities and the
nature of such liabilities as is reasonably necessary in order to determine the
former Cornerstone Partner's adjusted tax basis in its EOP OP Units and at-risk
amount; (iii) in deciding whether or not to grant such request, EOP Partnership
shall be entitled to take into account all factors related to EOP Partnership,
including, without limitation, the existing and anticipated debt structure of
EOP Partnership, the tax situations of other holders of EOP OP Units and the
effect that such a deficit restoration commitment might have on their tax
situation, and the anticipated term long term business needs of EOP; (iv) in no
event shall EOP Partnership be required to incur additional indebtedness that
would be considered a "recourse liability" for purposes of Section 752 of the
Code to facilitate such additional deficit capital account restoration
commitments; and (v) EOP Partnership's only obligation shall be to act in good
faith, and a former Cornerstone Partner's exclusive remedy under such provision
would be an action for specific performance, with no entitlement to monetary
damages.

     5.5 Public Announcements. Each party will consult with each other party
before issuing, and provide each other the opportunity to review and comment
upon, any press release or other written public statements, including, without
limitation, any press release or other written public statement which address in
any manner the transactions contemplated by this Agreement, and shall not issue
any such press release or make any such written public statement prior to such
consultation, except as may be required by applicable law, court process or by
obligations pursuant to any listing agreement with any national securities
exchange. The parties agree that the initial press release to be issued with
respect to the transactions contemplated by this Agreement will be in the form
agreed to by the parties prior to the execution of this Agreement.

     5.6 Listing. EOP shall use commercially reasonable efforts to cause the EOP
Common Shares to be issued in the Merger, and the EOP Common Shares reserved for
issuance upon redemption of EOP OP Units issued in the Partnership Merger, to be
approved for listing on the NYSE, subject to official notice of issuance, prior
to the Effective Time.

     5.7 Transfer and Gains Taxes. Each party shall cooperate in the
preparation, execution and filing of all returns, questionnaires, applications
or other documents regarding any real property transfer or gains, sales, use,
transfer, value added stock transfer and stamp taxes, any transfer, recording,
registration and other fees and any similar taxes which become payable in
connection with the transactions contemplated by this Agreement (together with
any related interests, penalties or additions to tax, "Transfer and Gains
Taxes"). From and after the Effective Time, EOP shall pay or cause EOP Operating
Partnership, as

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appropriate, to pay or cause to be paid, without deduction or withholding from
any amounts payable to the holders of EOP Common Shares or EOP OP Units, as
applicable, all Transfer and Gains Taxes (which term shall not in any event be
construed to include for these purposes any Tax imposed under the Code).

     5.8 Benefit Plans and Other Employee Arrangements.

     (a) Benefit Plans. After the Effective Time, all employees of Cornerstone
who are employed by the Surviving Trust shall, at the option of the Surviving
Trust, either continue to be eligible to participate in an "employee benefit
plan", as defined in Section 3(3) of ERISA, of Cornerstone which is, at the
option of the Surviving Trust, continued by the Surviving Trust, or
alternatively shall be eligible to participate in the same manner as other
similarly situated employees of the Surviving Trust who were formerly employees
of EOP in any "employee benefit plan," as defined in Section 3(3) of ERISA,
sponsored or maintained by the Surviving Trust after the Effective Time. With
respect to each such employee benefit plan, service with Cornerstone or any
Cornerstone Subsidiary (as applicable) and the predecessor of any of them shall
be included for purposes of determining eligibility to participate, vesting (if
applicable) and determination of the level of entitlement to, benefits under
such employee benefit plan. EOP shall, or shall cause the Surviving Trust and
its Subsidiaries to, (i) waive all limitations, as to preexisting conditions
exclusions and waiting periods with respect to participation and coverage
requirements applicable to all employees of Cornerstone who are employed by the
Surviving Trust under any welfare plan that such employees may be eligible to
participate in after the Effective Time, other than limitations or waiting
periods that are already in effect with respect to such employees and that have
not been satisfied as of the Effective Time under any welfare plan maintained
for such employees immediately prior to the Effective Time, and (ii) provide
each such employee of Cornerstone who is employed by the Surviving Trust with
credit for any co-payments and deductibles paid prior to the Effective Time in
satisfying any applicable deductible or out-of-pocket requirements under any
welfare plans that such employees are eligible to participate in after the
Effective Time.

     (b) Stock Option and Restricted Stock Plans. The stock option plans or
programs of Cornerstone and the restricted stock plans or programs of
Cornerstone shall be discontinued.

     (c) Cornerstone Stock Options. As of the Effective Time, each outstanding
Cornerstone Stock Option shall, whether or not then vested or exercisable,
effective as of the Effective Time, become fully exercisable and vested and each
such Cornerstone Stock Option shall be automatically converted at the Effective
Time into an option (a "Substituted Option") to purchase a number of shares of
EOP Common Shares equal to the number of shares of Cornerstone Common Stock that
could have been purchased (assuming full vesting) under such Cornerstone Stock
Option multiplied by 0.7009 (rounded down to the nearest whole number of shares
of Cornerstone Common Stock) at an exercise price per share of EOP Common Shares
equal to the per-share option exercise price specified in the Cornerstone Stock
Option divided by 0.7009 (rounded up to the nearest whole cent). Such
Substituted Option shall otherwise be subject to the same terms and conditions
as such Cornerstone Stock Option. For purposes of expiration and otherwise, the
date of grant of the Substituted Option shall be the date on which the
corresponding Cornerstone Stock Option was granted. If the holder of such
Cornerstone Stock Option surrenders such option after the Effective Time and
prior to 11:59 p.m., Eastern Time, on the second business day immediately
following the Effective Time, EOP shall, subject to reduction for required
withholding taxes, pay to each such holder of Cornerstone Stock Options an
amount in cash in respect thereof equal to the product of (i) the excess, if
any, of $18.00 over the exercise price of such Cornerstone Stock Option and (ii)
the number of shares of Cornerstone Common Stock subject thereto. At the
Effective Time, (i) all references in the related stock option agreements to
Cornerstone shall be deemed to refer to EOP and (ii) EOP shall assume all of
Cornerstone's obligations with respect to Cornerstone Stock Options as so
amended. As promptly as reasonably practicable after the Effective Time, EOP
shall issue to each holder of an outstanding Cornerstone Stock Option a document
evidencing the foregoing assumption by EOP.

     In respect of each Cornerstone Stock Option assumed by EOP and converted
into a Substituted Option, and the EOP Common Shares underlying such Substituted
Option, EOP shall, as soon as

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practicable after the Effective Time, file and keep current a Registration
Statement on Form S-8 or other appropriate registration statement for as long as
Substituted Options remain outstanding.

     (d) Restricted Stock. All unvested shares of restricted stock of
Cornerstone set forth in Schedule 5.8(d) of the Cornerstone Disclosure Schedule,
shall, by virtue of this Agreement and without further action of Cornerstone,
EOP or the holder of such shares of restricted stock, to the extent required in
the plan, agreement or instrument pursuant to which such shares of restricted
stock were granted, vest and become free of all restrictions immediately prior
to the Effective Time and shall be converted into the Merger Consideration
pursuant to Section 1.10.

     (e) Retention Agreements and Retention Plan. From and after the Effective
Time, EOP or EOP Partnership shall assume the obligations of Cornerstone under
the Retention Agreements and the Cornerstone retention plan set forth on
Schedule 5.9(e) of the Cornerstone Disclosure Letter. The transactions
contemplated by this Agreement shall be deemed a "Change in Control" for
purposes of such agreements, and EOP shall perform the obligations of
Cornerstone under such agreements and plan in accordance with the terms thereof.

     (f) Withholding. To the extent required by applicable law, Cornerstone
shall require each employee who exercises a Cornerstone Stock Option or who
receives Cornerstone Common Stock pursuant to any existing commitment to pay to
Cornerstone in cash or Cornerstone Common Stock an amount sufficient to satisfy
in full Cornerstone's obligation to withhold Taxes incurred by reason of such
exercise or issuance (unless and to the extent such withholding is satisfied
pursuant to the provision regarding withholding in Section 1.15(c)).

     5.9 Indemnification.

     (a) From and after the Effective Time, EOP and EOP Partnership
(collectively, the "Indemnifying Parties") shall provide exculpation and
indemnification for each person who is now or has been at any time prior to the
date hereof or who becomes prior to the Effective Time of the Merger, an officer
or director of Cornerstone or any Cornerstone Subsidiary (the "Indemnified
Parties") which is the same as the exculpation and indemnification provided to
the Indemnified Parties by Cornerstone and the Cornerstone Subsidiaries
immediately prior to the Effective Time of the Merger in its charter, Bylaws or
in its partnership, operating or similar agreement, as in effect on the date
hereof.

     (b) In addition to the rights provided in Section 5.9(a) above, in the
event of any threatened or actual claim, action, suit, proceeding or
investigation, whether civil, criminal or administrative, including, without
limitation, any action by or on behalf of any or all security holders of
Cornerstone or EOP, or any Cornerstone Subsidiary or EOP Subsidiary, or by or in
the right of Cornerstone or EOP, or any Cornerstone Subsidiary or EOP
Subsidiary, or any claim, action, suit, proceeding or investigation in which any
person who is now, or has been, at any time prior to the date hereof, or who
becomes prior to the Effective Time of the Merger, an officer, employee or
director of Cornerstone or any Cornerstone Subsidiary (the "Indemnification
Parties") is, or is threatened to be, made a party based in whole or in part on,
or arising in whole or in part out of, or pertaining to (i) the fact that he is
or was an officer, employee or director of Cornerstone or any of the Cornerstone
Subsidiaries or any action or omission by such person in his capacity as a
director, or (ii) this Agreement or the transactions contemplated by this
Agreement, whether in any case asserted or arising before or after the Effective
Time of the Merger, the Indemnifying Parties shall, from and after the Effective
Time of the Merger, indemnify and hold harmless, as and to the full extent
permitted by applicable law, each Indemnification Party against any losses,
claims, liabilities, expenses (including reasonable attorneys' fees and
expenses), judgments, fines and amounts paid in settlement in accordance
herewith in connection with any such threatened or actual claim, action, suit,
proceeding or investigation. Any Indemnification Party proposing to assert the
right to be indemnified under this Section 5.9(b) shall, promptly after receipt
of notice of commencement of any action against such Indemnification Party in
respect of which a claim is to be made under this Section 5.9(b) against the
Indemnifying Parties, notify the Indemnifying Parties of the commencement of
such action, enclosing a copy of all papers served; provided, however, that the
failure to provide such notice shall not affect the obligations of the
Indemnifying Parties except to the extent such failure to notify
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materially prejudices the Indemnifying Parties' ability to defend such claim,
action, suit, proceeding or investigation; and provided, further, however, that,
in the case of any action pending at the Effective Time of the Merger,
notification pursuant to this Section 5.9(b) shall be received by EOP prior to
such Effective Time. If any such action is brought against any of the
Indemnification Parties and such Indemnification Parties notify the Indemnifying
Parties of its commencement, the Indemnifying Parties will be entitled to
participate in and, to the extent that they elect by delivering written notice
to such Indemnification Parties promptly after receiving notice of the
commencement of the action from the Indemnification Parties, to assume the
defense of the action and after notice from the Indemnifying Parties to the
Indemnification Parties of their election to assume the defense, the
Indemnifying Parties will not be liable to the Indemnification Parties for any
legal or other expenses except as provided below. If the Indemnifying Parties
assume the defense, the Indemnifying Parties shall have the right to settle such
action without the consent of the Indemnification Parties; provided, however,
that the Indemnifying Parties shall be required to obtain such consent (which
consent shall not be unreasonably withheld) if the settlement includes any
admission of wrongdoing on the part of the Indemnification Parties or any decree
or restriction on the Indemnification Parties; provided, further, that no
Indemnifying Parties, in the defense of any such action shall, except with the
consent of the Indemnification Parties (which consent shall not be unreasonably
withheld), consent to entry of any judgment or enter into any settlement that
does not include as an unconditional term thereof the giving by the claimant or
plaintiff to such Indemnification Parties of a release from all liability with
respect to such action. The Indemnification Parties will have the right to
employ their own counsel in any such action, but the fees, expenses and other
charges of such counsel will be at the expense of such Indemnification Parties
unless (i) the employment of counsel by the Indemnification Parties has been
authorized in writing by the Indemnifying Parties, (ii) the Indemnification
Parties have reasonably concluded (based on written advice of counsel to the
Indemnification Parties) that there may be legal defenses available to them that
are different from or in addition to and inconsistent with those available to
the Indemnifying Parties, (iii) a conflict or potential conflict exists (based
on written advice of counsel to the Indemnification Parties) between the
Indemnification Parties and the Indemnifying Parties (in which case the
Indemnifying Parties will not have the right to direct the defense of such
action on behalf of the Indemnification Parties) or (iv) the Indemnifying
Parties have not in fact employed counsel to assume the defense of such action
within a reasonable time after receiving notice of the commencement of the
action from the Indemnification Parties, in each of which cases the reasonable
fees, disbursements and other charges of counsel will be at the expense of the
Indemnifying Parties and shall promptly be paid by each Indemnifying Party as
they become due and payable in advance of the final disposition of the claim,
action, suit, proceeding or investigation to the fullest extent and in the
manner permitted by law; provided, however, that in no event shall any
contingent fee arrangement be considered reasonable. Notwithstanding the
foregoing, the Indemnifying Parties shall not be obligated to advance any
expenses or costs prior to receipt of an undertaking by or on behalf of the
Indemnification Party to repay any expenses advanced if it shall ultimately be
determined that the Indemnification Party is not entitled to be indemnified
against such expense. It is understood that the Indemnifying Parties shall not,
in connection with any proceeding or related proceedings in the same
jurisdiction, be liable for the reasonable fees, disbursements and other charges
of more than one separate firm admitted to practice in such jurisdiction at any
one time for all such Indemnification Parties unless (a) the employment of more
than one counsel has been authorized in writing by the Indemnifying Parties, (b)
any of the Indemnification Parties have reasonably concluded (based on written
advice of counsel to the Indemnification Parties) that there may be legal
defenses available to them that are different from or in addition to and
inconsistent with those available to other Indemnification Parties or (c) a
conflict or potential conflict exists (based on written advice of counsel to the
Indemnification Parties) between any of the Indemnification Parties and the
other Indemnification Parties, in each case of which the Indemnifying Parties
shall be obligated to pay the reasonable fees and expenses of such additional
counsel or counsels. Notwithstanding anything to the contrary set forth in this
Agreement, the Indemnifying Parties (i) shall not be liable for any settlement
effected without their prior written consent and (ii) shall not have any
obligation hereunder to any Indemnification Party to the extent that a court of
competent jurisdiction shall determine in a final and non-appealable order that
such indemnification is prohibited by applicable law. In the event of a final
and non-appealable determination
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by a court that any payment of expenses is prohibited by applicable law, the
Indemnification Parties shall promptly refund to the Indemnifying Parties the
amount of all such expenses theretofore advanced pursuant hereto.

     (c) At or prior to the Effective Time of the Merger, EOP shall purchase
directors' and officers' liability insurance covering acts or omissions
occurring prior to the Effective Time of the Merger for a period of six years
with respect to those persons who are currently covered by Cornerstone's
directors' and officers' liability insurance policy on terms with respect to
such coverage and amount no less favorable to Cornerstone's directors and
officers currently covered by such insurance than those of such policy in effect
on the date hereof.

     (d) This Section 5.9 is intended for the irrevocable benefit of, and to
grant third-party rights to, the Indemnified Parties, the Indemnification
Parties and their successors, assigns and heirs and shall be binding on all
successors and assigns of EOP and EOP Operating Partnership. Each of the
Indemnified Parties and the Indemnification Parties shall be entitled to enforce
the covenants contained in this Section 5.9 and EOP and EOP Partnership
acknowledge and agree that each Indemnified Party and Indemnification Party
would suffer irreparable harm and that no adequate remedy at law exists for a
breach of such covenants and such Indemnified Party or such Indemnification
Party shall be entitled to injunctive relief and specific performance in the
event of any breach of any provision in this Section 5.9.

     (e) If EOP or EOP Partnership or any of its respective successors or
assigns (i) consolidates with or merges into any other person and shall not be
the continuing or surviving corporation or entity of such consolidation or
merger or (ii) transfers all or substantially all of its properties and assets
to any person, then, and in each such case the successors and assigns of such
entity shall assume the obligations set forth in this Section 5.9, which
obligations are expressly intended to be for the irrevocable benefit of, and
shall be enforceable by, each director and officer covered hereby.

     5.10 Declaration of Dividends and Distributions. From and after the date of
this Agreement, neither Cornerstone nor EOP shall make any dividend or
distribution to its respective stockholders or shareholders without the prior
written consent of the other party; provided, however, the written consent of
the other party shall not be required for the authorization and payment of (a)
distributions at their respective stated dividend or distribution rates with
respect to EOP Preferred Shares or Cornerstone 7% Preferred Stock, (b) quarterly
distribution with respect to the Cornerstone Common Stock of up to $0.24 per
share for the quarter ending March 31, 2000 and up to $0.31 per share thereafter
and (c) quarterly distributions with respect to the EOP Common Share of up to
$0.42 per share for the quarter ending March 31, 2000 and for each quarter
thereafter; provided, however, except for the record date previously set on
January 31, 2000, the record date for each distribution with respect to the
Cornerstone Common Stock shall be the same date as the record date for the
quarterly distribution for the EOP Common Shares, as provided to Cornerstone by
notice not less than twenty (20) business days prior to the record date for any
quarterly EOP distribution. From and after the date of this Agreement,
Cornerstone Partnership shall not make any distribution to the holders of
Cornerstone OP Units except a distribution per Cornerstone OP Unit in the same
amount as a dividend per share of Cornerstone Common Stock permitted pursuant to
this Section 5.10, with the same record and payment dates as such dividend on
the Cornerstone Common Stock. The foregoing restrictions shall not apply,
however, to the extent a distribution (or an increase in a distribution) by
Cornerstone or EOP is necessary for Cornerstone or EOP, as applicable, to
maintain REIT status, avoid the incurrence of any taxes under Section 857 of the
Code, avoid the imposition of any excise taxes under Section 4981 of the Code,
or avoid the need to make one or more extraordinary or disproportionately larger
distributions to meet any of the three preceding objectives.

     5.11 Transfer of Non-Controlled Subsidiary Voting Shares. At the Closing
and pursuant to the Stock Purchase Agreement, each of the holders of voting
capital stock of the Cornerstone Non-controlled Subsidiary (other than
Cornerstone Partnership, to the extent it owns any such voting capital stock)
shall transfer to EOP NCS Sub or such person or persons as EOP NCS Sub shall
designate by written notice delivered to them prior to the Closing, all of the
shares of each such Company owned by them, constituting all the outstanding
shares of such companies which are not owned by Cornerstone Partnership,

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for an aggregate consideration in an amount equal to the purchase price set
forth in the Stock Purchase Agreement. EOP shall use commercially reasonable
efforts to cause EOP NCS Sub to perform its obligations under the Stock Purchase
Agreement

     5.12 Notices. EOP shall provide such notice to its preferred shareholders
of the Merger as is required under Maryland law or the EOP Declaration of Trust.

     5.13 Resignations. On the Closing Date, Cornerstone shall cause the
directors and officers of Cornerstone and of each of the Cornerstone
Subsidiaries to submit their resignations from such positions, effective as of
the Effective Time of the Merger.

     5.14 Assumption of Existing Tax Protection Agreements. Effective as of the
Effective Time of the Partnership Merger, EOP and EOP Partnership shall assume
the obligations of Cornerstone, Cornerstone Partnership and/or the applicable
Cornerstone Subsidiary, as the case may be, under the Tax Protection Agreements
as described in Schedule 2.18(j) to the Cornerstone Disclosure Letter.
Immediately prior to the Effective Time of the Partnership Merger, EOP and EOP
Partnership shall enter into agreements with Cornerstone and Cornerstone
Partnership, for the benefit of and enforceable by the individuals and entities
who are intended to be protected by the provisions of the Tax Protection
Agreements, confirming such assumption effective as of the Effective Time of the
Partnership Merger.

     5.15 EOP Partnership Agreement. At the Closing, EOP Partnership shall
assume and perform any obligations that Cornerstone Partnership or any
Cornerstone Subsidiary has immediately prior to the Effective Time to issue
securities in accordance with the terms of any partnership or other agreement to
which Cornerstone Partnership or such Cornerstone Subsidiary is a party and that
are described on Schedule 5.15, in the same manner and to the same extent that
Cornerstone Partnership or such Cornerstone Subsidiary would be required to
perform such obligation if no Merger had been consummated.

     5.16 Registration Rights Agreements. At the Closing, (a) Cornerstone shall
assign and EOP shall assume by appropriate instrument the Registration Rights
Agreements described on Schedule 5.16 to the Cornerstone Disclosure Letter, and
(b) Cornerstone shall assign and EOP shall assume the obligations of Cornerstone
under the Amended and Restated Registration Rights and Voting Agreement dated
December 16, 1998 between Cornerstone, PGGM and Dutch Institutional Holding
Company, Inc., as and to the extent set forth in PGGM's Cornerstone Voting
Agreement.

     5.17 Cornerstone Convertible Promissory Note. Following the Effective Time
of the Mergers, the holders of the Cornerstone Convertible Promissory Note shall
have the right to obtain upon the exercise of its conversion rights pursuant to
such Cornerstone Convertible Promissory Note, in lieu of each share of
Cornerstone Common Stock theretofor issuable upon exercise of such conversion
rights, EOP Common Shares that it would have owned immediately after the Merger
if it had converted the Cornerstone Convertible Promissory Note immediately
before the Effective Time of the Merger.

                                   ARTICLE 6

                                   CONDITIONS

     6.1 Conditions to Each Party's Obligation to Effect the Mergers. The
obligations of each party to effect the Mergers and to consummate the other
transactions contemplated by this Agreement to occur on the Closing Date shall
be subject to the fulfillment at or prior to the Closing Date of the following
conditions:

     (a) Shareholder and Partner Approvals. The Cornerstone Stockholder
Approvals, the EOP Shareholder Approvals and the Partner Approvals shall have
been obtained.

     (b) HSR Act. The waiting period (and any extension thereof) applicable to
the Partnership Merger, the Merger or the transactions contemplated by the Stock
Purchase Agreement under the HSR Act, if

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applicable to the Partnership Merger, the Merger or and the transactions
contemplated by the Stock Purchase Agreement, shall have expired or been
terminated.

     (c) Listing of Shares. The NYSE shall have approved for listing the EOP
Common Shares to be issued in the Merger and the EOP Common Shares reserved for
issuance upon redemption of EOP OP Units issued in the Partnership Merger,
subject to official notice of issuance.

     (d) Form S-4. The Form S-4 shall have become effective under the Securities
Act and shall not be the subject of any stop order or proceedings by the SEC
seeking a stop order.

     (e) No Injunctions or Restraints. No temporary restraining order,
preliminary or permanent injunction or other order issued by any court of
competent jurisdiction or other legal restraint or prohibition preventing the
consummation of the Mergers or any of the other transactions contemplated hereby
shall be in effect.

     (f) Blue Sky Laws. EOP and EOP Partnership shall have received all state
securities or "blue sky" permits and other authorizations necessary to issue the
EOP Common Shares and EOP OP Units issuable in the Mergers.

     6.2 Conditions to Obligations of EOP and EOP Partnership. The obligations
of EOP and EOP Partnership to effect the Mergers and to consummate the other
transactions contemplated to occur on the Closing Date are further subject to
the following conditions, any one or more of which may be waived by EOP:

     (a) Representations and Warranties. Each of the representations and
warranties of Cornerstone and Cornerstone Partnership set forth in this
Agreement, disregarding all qualifications and exceptions contained therein
relating to materiality or Cornerstone Material Adverse Effect, shall be true
and correct as of the date of this Agreement and as of the Closing Date as
though made on and as of the Closing Date (except to the extent that such
representations and warranties are expressly limited by their terms to another
date, in which case such representations and warranties shall be true and
correct as of such other date), except where the failure of such representations
and warranties to be true and correct would not, individually or in the
aggregate, reasonably be expected to have a Cornerstone Material Adverse Effect;
and EOP shall have received a certificate (which certificate may be qualified by
Knowledge to the same extent as the representations and warranties of
Cornerstone and Cornerstone Partnership contained herein are so qualified)
signed on behalf of Cornerstone by the chief executive officer or the chief
financial officer of Cornerstone, in such capacity, to such effect.

     (b) Performance of Obligations of Cornerstone and Cornerstone
Partnership.  Cornerstone and Cornerstone Partnership shall have performed in
all material respects all obligations required to be performed by them under
this Agreement at or prior to the Effective Time, and EOP shall have received a
certificate signed on behalf of Cornerstone by the chief executive officer or
the chief operating officer of Cornerstone, in such capacity, to such effect.

     (c) Material Adverse Change. Since the date of this Agreement, there shall
have been no Cornerstone Material Adverse Change and EOP shall have received a
certificate of the chief executive officer or chief operating officer of
Cornerstone, in such capacity, certifying to such effect.

     (d) Tax Opinions Relating to REIT Status and Partnership Status. EOP shall
have received (i) an opinion of King & Spalding or other counsel to Cornerstone
reasonably satisfactory to EOP, dated as of the Closing Date, to the effect
that, commencing with its taxable year ended December 31, 1997, (x) Cornerstone
was organized and has operated in conformity with the requirements for
qualification as a REIT under the Code, and (y) Cornerstone Partnership has been
during and since December 23, 1997, and continues to be, treated for federal
income tax purposes as a partnership and not as a corporation or association
taxable as a corporation (with customary exceptions, assumptions and
qualifications and based upon customary representations) and (ii) an opinion of
Hogan & Hartson L.L.P. or other counsel to EOP reasonably satisfactory to
Cornerstone, dated as of the Closing Date, to the effect that, commencing with
its taxable year ended December 31, 1997, EOP was organized and has operated in
conformity with the

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requirements for qualification as a REIT under the Code and that, after giving
effect to the Merger, EOP's proposed method of operation will enable it to
continue to meet the requirements for qualification and taxation as a REIT under
the Code (with customary exceptions, assumptions and qualifications and based
upon customary representations and based upon and subject to the opinion of
counsel to Cornerstone described in clause (i) above).

     (e) Tax Opinion Relating to the Merger. EOP shall have received an opinion
dated the Closing Date from Hogan & Hartson L.L.P. or other counsel reasonably
satisfactory to EOP, based upon customary certificates and letters, which
letters and certificates are to be in a form to be agreed upon by the parties
and dated the Closing Date, to the effect that the Merger will qualify as a
reorganization under the provisions of Section 368(a) of the Code.

     (f) "Comfort" Letter. EOP and EOP Partnership shall have received a
"comfort" letter from PricewaterhouseCoopers LLP, as described in Section
5.1(b).

     (g) Noncompetition Agreements. Each of William Wilson III and John S. Moody
shall have entered into noncompetition and confidentiality agreements
substantially in the forms set forth in Schedule 6.2(g) hereto.

     6.3 Conditions to Obligations of Cornerstone and Cornerstone
Partnership.  The obligations of Cornerstone and Cornerstone Partnership to
effect the Mergers and to consummate the other transactions contemplated to
occur on the Closing Date is further subject to the following conditions, any
one or more of which may be waived by Cornerstone:

     (a) Representations and Warranties. Each of the representations and
warranties of EOP and EOP Partnership set forth in this Agreement, disregarding
all qualifications and exceptions contained therein relating to materiality or
EOP Material Adverse Effect, shall be true and correct as of the date of this
Agreement and as of the Closing Date as though made on and as of the Closing
Date (except to the extent that such representations and warranties are
expressly limited by their terms to another date, in which case such
representations and warranties shall be true and correct as of such other date),
except where the failure of such representations and warranties to be true and
correct would not, individually or in the aggregate, reasonably be expected to
have a EOP Material Adverse Effect; and Cornerstone shall have received a
certificate (which certificate may be qualified by Knowledge to the same extent
as the representations and warranties of EOP and EOP Partnership contained
herein are so qualified) signed on behalf of EOP by the chief executive officer
or the chief financial officer of EOP, in such capacity, to such effect.

     (b) Performance of Obligations of EOP and EOP Partnership. EOP and EOP
Partnership shall have performed in all material respects all obligations
required to be performed by it under this Agreement at or prior to the Effective
Time, and Cornerstone shall have received a certificate of EOP signed on behalf
of EOP by a duly authorized executive officer of EOP, in such capacity, to such
effect.

     (c) Material Adverse Change. Since the date of this Agreement, there shall
have been no EOP Material Adverse Change and Cornerstone shall have received a
certificate of a duly authorized executive officer of EOP, in such capacity,
certifying to such effect.

     (d) Tax Opinions Relating to REIT Status and Partnership Status.
Cornerstone shall have received the opinion of Hogan & Hartson L.L.P. or other
counsel to EOP reasonably satisfactory to Cornerstone, dated as of the Closing
Date, that, commencing with its taxable year ended December 31, 1997, (i) EOP
was organized and has operated in conformity with the requirements for
qualification as a REIT under the Code and that, after giving effect to the
Merger, EOP's proposed method of operation will enable it to continue to meet
the requirements for qualification and taxation as a REIT under the Code (with
customary exceptions, assumptions and qualifications and based upon customary
representations and based upon and subject to the opinion of counsel to
Cornerstone described in Section 6.2(d) of this Agreement), (ii) BeaMet was
organized and has operated in conformity with the requirements for qualification
as a REIT under the Code (with customary exceptions, assumptions and
qualifications and based upon customary representations), and (iii) EOP
Partnership has been during and since 1997, and continues to
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be, treated for federal income tax purposes as a partnership and not as a
corporation or association taxable as a corporation (with customary exceptions,
assumptions and qualifications and based upon customary representations).

     (e) Tax Opinion Relating to the Merger. Cornerstone shall have received an
opinion dated the Closing Date from King & Spalding or other counsel reasonably
satisfactory to Cornerstone, based upon customary certificates and letters,
which letters and certificates are to be in a form to be agreed upon by the
parties and dated the Closing Date, to the effect that the Merger will qualify
as a reorganization under the provisions of Section 368(a) of the Code.

     (f) Proposed EOP Charter Amendment Relating to Domestically Controlled REIT
Status. The EOP Shareholders shall have approved the Proposed EOP Charter
Amendment Relating to Domestically Controlled REIT Status at the EOP
Shareholders Meeting.

     (g) "Comfort" Letter. Cornerstone and Cornerstone Partnership shall have
received a "comfort" letter from Ernst & Young LLP, as described in Section
5.1(b).

     (h) Certificate Regarding "Domestically Controlled REIT" Status to PGGM.
EOP shall have delivered to Stichting Pensioenfonds voor de Gezondheid,
Geestelijke en Maatschappelijke Belangen ("PGGM") a certification dated within
fifteen (15) days of the Closing Date that to EOP's knowledge, after reasonable
inquiry, EOP is a "domestically controlled REIT" within the meaning of Section
897(h)(4)(B) of the Code as of the date thereof. For purposes of such
certification, reasonable inquiry shall include (but not necessarily be limited
to) review of all Schedule 13D and 13G filings made under the Exchange Act with
the SEC with respect to EOP, all IRS Form 1042 filings made by or on behalf of
EOP, the list of EOP's registered shareholders as of a date within 60 days of
such certificate (and to the extent reasonably available, as of a date within 60
days of the end of each of 1997, 1998, and 1999), a list of "non-objecting
beneficial owners" of shares of EOP obtained as of a date within 60 days of such
certificate (and to the extent reasonably available, as of a date within 60 days
of the end of each of 1997, 1998, and 1999), and a report of a shareholder
tracking service obtained within 60 days of such certificate (together with such
other reports as are in the possession of EOP). Such certificate shall be
accompanied by copies of information that has been obtained or relied upon by
EOP for purposes of such certificate, provided that PGGM shall have executed an
agreement with EOP to treat such information as confidential and to use such
information solely for the purposes of evaluating the accuracy of such
certification.

                                   ARTICLE 7

                       TERMINATION, AMENDMENT AND WAIVER

     7.1 Termination. This Agreement may be terminated at any time prior to the
Effective Time of the Partnership Merger, whether such action occurs before or
after any of the Cornerstone Stockholder Approvals, the EOP Shareholder
Approvals or either of the Cornerstone Partner Approvals are obtained:

     (a) by mutual written consent duly authorized by the Board of Trustees of
EOP and the Board of Directors of Cornerstone;

     (b) by EOP, upon a breach of or failure to perform any representation,
warranty, covenant, obligation or agreement on the part of Cornerstone or
Cornerstone Partnership set forth in this Agreement, or if any representation or
warranty of Cornerstone or Cornerstone Partnership shall become untrue, in
either case such that the conditions set forth in Section 6.2(a) or Section
6.2(b), as the case may be, would be incapable of being satisfied by December
31, 2000 (or as otherwise extended);

     (c) by Cornerstone, upon a breach of any representation, warranty, covenant
obligation or agreement on the part of EOP or EOP Partnership set forth in this
Agreement, or if any representation or warranty of EOP or EOP Partnership shall
become untrue, in either case such that the conditions set forth in Section
6.3(a) or Section 6.3(b), as the case may be, would be incapable of being
satisfied by December 31, 2000 (or as otherwise extended);

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     (d) by either EOP or Cornerstone, if any judgment, injunction, order,
decree or action by any Governmental Entity of competent authority preventing
the consummation of either of the Mergers shall have become final and
non-appealable;

     (e) by either EOP or Cornerstone, if the Mergers shall not have been
consummated before December 31, 2000; provided, however, that a party may not
terminate pursuant to this clause (e) if the terminating party shall have
breached in any material respect its obligations under this Agreement in any
manner that shall have caused either of the Mergers not to have been consummated
by such date;

     (f) by either EOP or Cornerstone (unless Cornerstone or Cornerstone
Partnership is in breach in any material respect of its obligations under
Section 5.1) if, upon a vote at a duly held Cornerstone Stockholders Meeting or
any adjournment thereof, the Cornerstone Stockholder Approvals shall not have
been obtained as contemplated by Section 5.1 or if the Cornerstone Partner
Approvals have not been obtained as contemplated by Section 5.1;

     (g) by either Cornerstone or EOP (unless EOP or EOP Partnership is in
breach in any material respect of its obligations under Section 5.1 if, upon a
vote at a duly held EOP Shareholders Meeting or any adjournment thereof, the EOP
Shareholder Approvals shall not have been obtained as contemplated by Section
5.1 or if the EOP Partner Approvals have not been obtained as contemplated by
Section 5.1;

     (h) by Cornerstone (i) if the Board of Directors of Cornerstone shall have
withdrawn, modified, amended or qualified in any manner adverse to EOP its
approval or recommendation of either of the Merger or this Agreement in
connection with, or approved or recommended, any Superior Acquisition Proposal,
or, (ii) in order to enter into a binding written agreement with respect to a
Superior Acquisition Proposal, provided that, in each case, Cornerstone shall
have complied with the terms of Section 4.3 and, prior to terminating pursuant
to this Section 7.1(h), has paid to EOP Partnership the Break-Up Fee (as defined
herein) as provided by Section 7.2 hereof; and

     (i) by EOP, if (1) the Board of Directors of Cornerstone shall have failed
to recommend or withdrawn, modified, amended or qualified, or proposed publicly
not to recommend or to withdraw, modify, amend or qualify, in any manner adverse
to EOP its approval or recommendation of either of the Mergers or this Agreement
or approved or recommended any Superior Acquisition Proposal, (2) following the
announcement or receipt of an Acquisition Proposal, Cornerstone shall have
failed to call the Cornerstone Stockholders Meeting in accordance with Section
5.1(a) or failed to prepare and mail to its stockholders the Joint Proxy
Statement in accordance with Section 5.1(a) or 5.1(b), or (3) the Board of
Directors of Cornerstone or any committee thereof shall have resolved to do any
of the foregoing.

     7.2 Certain Fees and Expenses. If this Agreement shall be terminated (i)
pursuant to Section 7.1(h), 7.1(i)(1) or 7.1(i)(3), then Cornerstone and
Cornerstone Partnership thereupon shall pay to EOP Partnership a fee equal to
the Break-Up Fee (as defined herein), and (ii) pursuant to Section 7.1(b) or
7.1(f), then Cornerstone and Cornerstone Partnership shall pay to EOP
Partnership (provided that Cornerstone was not entitled to terminate this
Agreement pursuant to Section 7.1(c) at the time of such termination) an amount
equal to the Break-Up Expenses (as defined herein). If this Agreement shall be
terminated pursuant to Section 7.1(c) or 7.1(g), then EOP and EOP Partnership
shall pay to Cornerstone Partnership (provided that EOP was not entitled to
terminate this Agreement pursuant to Section 7.1(b) at the time of such
termination) an amount equal to the Break-Up Expenses. If this Agreement shall
be terminated pursuant to Section 7.1(b), 7.1(d) (if primarily resulting from
any action or inaction of Cornerstone, Cornerstone Partnership or any
Cornerstone Subsidiary or the Cornerstone Non-controlled Subsidiary), 7.1(e),
7.1(f), 7.1(i)(2) and prior to the time of such termination an Acquisition
Proposal has been received by Cornerstone or Cornerstone Partnership, and either
prior to the termination of this Agreement or within twelve (12) months
thereafter, Cornerstone or Cornerstone Partnership enters into any written
agreement to consummate a transaction or series of transactions which, had such
agreement been proposed or negotiated during the term of this Agreement, would
have constituted an Acquisition Proposal pursuant to Section 4.3 (each, a
"Cornerstone Acquisition Agreement"), which is subsequently consummated (whether
or not any Cornerstone Acquisition Agreement relates to the same Acquisition

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<PAGE>   288

Proposal which had been received at the time of the termination of this
Agreement), then Cornerstone and Cornerstone Partnership shall pay the Break-Up
Fee to EOP Partnership.

     The payment of the Break-Up Fee shall be compensation for the loss suffered
by EOP and EOP Partnership as a result of the failure of the Mergers to be
consummated (including, without limitation, opportunity costs and out-of-pocket
costs and expenses) and to avoid the difficulty of determining damages under the
circumstances. The Break-Up Fee shall be paid by Cornerstone and Cornerstone
Partnership to EOP Partnership, or the Break-Up Expenses shall be paid by
Cornerstone and Cornerstone Partnership to EOP Partnership or EOP Partnership to
Cornerstone Partnership (as applicable), in immediately available funds within
two (2) business days after the date the event giving rise to the obligation to
make such payment occurred (except as otherwise provided in Section 7.1(h) or
7.1(i)). Cornerstone acknowledges that the agreements contained in this Section
7.2 are integral parts of this Agreement; accordingly, if Cornerstone and
Cornerstone Partnership fail to promptly pay the Break-Up Fee or Break-Up
Expenses due pursuant to this Section 7.2 and, in order to obtain payment, EOP
commences a suit which results in a judgment against Cornerstone or Cornerstone
Partnership for any amounts owed pursuant to this Section 7.2, Cornerstone and
Cornerstone Partnership shall pay to EOP its costs and expenses (including
attorneys' fees and expenses) in connection with such suit, together with
interest on the amount owed at the rate on six-month U.S. Treasury obligations
in effect on the date such payment was required to be made plus 300 basis
points.

     As used in this Agreement, "Break-Up Fee" shall be an amount equal to the
lesser of (i) $100,000,000 less Break-Up Expenses paid or payable under this
Section 7.2 (the "Base Amount") and (ii) the sum of (A) the maximum amount that
can be paid to EOP Partnership without causing EOP to fail to meet the
requirements of Sections 856(c)(2) and (3) of the Code determined as if the
payment of such amount did not constitute income described in Sections
856(c)(2)(A)-(H) and 856(c)(3)(A)-(I) of the Code ("Qualifying Income"), as
determined by independent accountants to EOP, and (B) in the event EOP receives
a letter from outside counsel (the "Break-Up Fee Tax Opinion") indicating that
EOP has received a ruling from the IRS holding that EOP Partnership's receipt of
the Base Amount would either constitute Qualifying Income or would be excluded
from gross income of EOP within the meaning of Sections 856(c)(2) and (3) of the
Code (the "REIT Requirements") or that the receipt by EOP Partnership of the
remaining balance of the Base Amount following the receipt of and pursuant to
such ruling would not be deemed constructively received prior thereto, the Base
Amount less the amount payable under clause (A) above. Cornerstone's and
Cornerstone Partnership's obligation to pay any unpaid portion of the Break-Up
Fee shall terminate three years from the date of this Agreement. In the event
that EOP Partnership is not able to receive the full Base Amount, Cornerstone
and Cornerstone Partnership shall place the unpaid amount in escrow and shall
not release any portion thereof to EOP Partnership unless and until Cornerstone
receives either one of the following: (i) a letter from EOP's independent
accountants indicating the maximum amount that can be paid at that time to EOP
Partnership without causing EOP to fail to meet the REIT Requirements or (ii) a
Break-Up Fee Tax Opinion, in either of which events Cornerstone and Cornerstone
Partnership shall pay to EOP Partnership the lesser of the unpaid Base Amount or
the maximum amount stated in the letter referred to in (i) above.

     The "Break-Up Expenses" payable to EOP Partnership or Cornerstone
Partnership, as the case may be (the "Recipient"), shall be an amount equal to
the lesser of (i) $7,500,000 or (ii) the Recipient's out-of-pocket expenses
incurred in connection with this Agreement and the transactions contemplated
hereby (including, without limitation, all attorneys', accountants' and
investment bankers' fees and expenses). If the Break-Up Expenses payable to the
Recipient exceed the maximum amount that can be paid to the Recipient without
causing the Recipient to fail to meet the requirements of Sections 856(c)(2) and
(3) of the Code determined as if the payment of such amount did not constitute
Qualifying Income, as determined by independent accountants to the Recipient
(the "Maximum Amount"), the amount initially payable to the Recipient shall be
limited to the Maximum Amount. If, however, within the three-year period
commencing on the date of this Agreement, the Recipient receives a Break-Up Fee
Tax Opinion indicating that it has received a ruling from the IRS holding that
the Recipient's receipt of the Break-Up

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<PAGE>   289

Expenses would either constitute Qualifying Income or would be excluded from
gross income of the Recipient within the meaning of the REIT Requirements or
that receipt by the Recipient of the balance of the Break-Up Expenses above the
Maximum Amount following the receipt of and pursuant to such ruling would not be
deemed constructively received prior thereto, the Recipient shall be entitled to
have payable to it the full amount of the Break-Up Expenses. The obligation of
EOP and EOP Partnership or Cornerstone and Cornerstone Partnership, as
applicable ("Payor"), to pay any unpaid portion of the Break-Up Expenses shall
terminate three years from the date of this Agreement. In the event that the
Recipient is not able to receive the full Break-Up Expenses, the Payor shall
place the unpaid amount in escrow and shall not release any portion thereof to
the Recipient unless and until the Payor receives either one of the following:
(i) a letter from the independent accountants of EOP or Cornerstone, as the case
may be, indicating the maximum amount that can be paid at that time to the
Recipient without causing it to fail to meet the REIT Requirements or (ii) a
Break-Up Expense Tax Opinion, in either of which events the Payor shall pay to
the Recipient the lesser of the unpaid Break-Up Expenses or the maximum amount
stated in the letter referred to in (i) above.

     7.3 Effect of Termination. In the event of termination of this Agreement by
either Cornerstone or EOP as provided in Section 7.1, this Agreement shall
forthwith become void and have no effect, without any liability or obligation on
the part of EOP, EOP Partnership, Cornerstone or Cornerstone Partnership, other
than the last sentence of Section 5.2, Section 7.2, this Section 7.3 and Article
8, and except to the extent that such termination results from a material breach
by any party of any of its representations, warranties, covenants or agreements
set forth in this Agreement.

     7.4 Amendment. This Agreement may be amended by the parties in writing by
action of the respective Board of Trustees or Board of Directors of EOP and
Cornerstone at any time before or after any Shareholder Approvals are obtained
and prior to the filing of the Articles of Merger with the Department; provided,
however, that, after the Shareholder Approvals and Partner Approvals are
obtained, no such amendment, modification or supplement shall be made which by
law requires the further approval of shareholders or partners without obtaining
such further approval. The parties agree to amend this Agreement in the manner
provided in the immediately preceding sentence to the extent required to (a)
continue the status of each party as a REIT or (b) preserve the Merger as a
reorganization under Section 368(a) of the Code.

     7.5 Extension; Waiver. At any time prior to the Effective Time, the parties
may (a) extend the time for the performance of any of the obligations or other
acts of the other party, (b) waive any inaccuracies in the representations and
warranties of the other party contained in this Agreement or in any document
delivered pursuant to this Agreement or (c) subject to the proviso of Section
7.4, waive compliance with any of the agreements or conditions of the other
party contained in this Agreement. Any agreement on the part of a party to any
such extension or waiver shall be valid only if set forth in an instrument in
writing signed on behalf of such party. The failure of any party to this
Agreement to assert any of its rights under this Agreement or otherwise shall
not constitute a waiver of those rights.

                                   ARTICLE 8

                               GENERAL PROVISIONS

     8.1 Nonsurvival of Representations and Warranties. None of the
representations and warranties in this Agreement or in any instrument delivered
pursuant to this Agreement confirming the representations and warranties in this
Agreement shall survive the Effective Time. This Section 8.1 shall not limit any
covenant or agreement of the parties which by its terms contemplates performance
after the Effective Time.

     8.2 Notices. All notices, requests, claims, demands and other
communications under this Agreement shall be in writing and shall be delivered
personally, sent by overnight courier (providing proof of delivery) to the
parties or sent by telecopy (providing confirmation of transmission) at the
following addresses or

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telecopy numbers (or at such other address or telecopy number for a party as
shall be specified by like notice):

     (a) if to EOP or EOP Partnership, to:

        Equity Office Properties Trust
        Two North Riverside Plaza, 22nd Floor
        Chicago, Illinois 60606
        Attention: Timothy H. Callahan, President
                   Stanley M. Stevens, Chief Counsel
        Fax No.: (312) 559-5021

     with a copy to:

        Hogan & Hartson L.L.P.
        555 Thirteenth Street, N.W.
        Washington, D.C. 20004-1109
        Attention: J. Warren Gorrell, Jr., Esq.
                   George P. Barsness, Esq.
        Fax No.: (202) 637-5910

     (b) if to Cornerstone or Cornerstone Partnership, to:

        Cornerstone Properties Inc.
        Tower 56
        126 East 56th Street, 6th Floor
        New York, New York 10022
        Attention: John S. Moody, President
        Fax No.: (212) 605-7199

     with a copy to:

        King & Spalding
        191 Peachtree Street
        Atlanta, GA 30303-1763
        Attention: William B. Fryer, Esq.
        Fax No.: (404) 572-5100

     All notices shall be deemed given only when actually received.

     8.3 Interpretation. When a reference is made in this Agreement to a
Section, such reference shall be to a Section of this Agreement unless otherwise
indicated. The table of contents and headings contained in this Agreement are
for reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement. Whenever the words "include", "includes" or
"including" are used in this Agreement, they shall be deemed to be followed by
the words "without limitation."

     8.4 Counterparts. This Agreement may be executed in one or more
counterparts, all of which shall be considered one and the same agreement and
shall become effective when one or more counterparts have been signed by each of
the parties and delivered to the other party.

     8.5 Entire Agreement; No Third-Party Beneficiaries. This Agreement, the
Cornerstone Disclosure Letter, the EOP Disclosure Letter, the Confidentiality
Agreement, the Voting Agreements and the other agreements entered into in
connection with the Mergers (a) constitute the entire agreement and supersede
all prior agreements and understandings, both written and oral between the
parties with respect to the subject matter of this Agreement and (b) except as
provided in Section 5.9 ("Third Party Provisions"), are not intended to confer
upon any person other than the parties hereto any rights or remedies.

     8.6 Governing Law. THE PARTNERSHIP MERGER SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF DELAWARE,

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REGARDLESS OF THE LAWS THAT MIGHT OTHERWISE GOVERN UNDER APPLICABLE PRINCIPLES
OF CONFLICT OF LAWS THEREOF. EXCEPT AS PROVIDED IN THE IMMEDIATELY PRECEDING
SENTENCE, THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE LAWS OF THE STATE OF MARYLAND, REGARDLESS OF THE LAWS THAT MIGHT OTHERWISE
GOVERN UNDER APPLICABLE PRINCIPLES OF CONFLICT OF LAWS THEREOF.

     8.7 Assignment. Neither this Agreement nor any of the rights, interests or
obligations under this Agreement shall be assigned or delegated, in whole or in
part, by operation of law or otherwise by any of the parties without the prior
written consent of the other parties. Subject to the preceding sentence, this
Agreement will be binding upon, inure to the benefit of, and be enforceable by,
the parties and their respective successors and assigns.

     8.8 Enforcement. The parties agree that irreparable damage would occur in
the event that any of the provisions of this Agreement were not performed in
accordance with their specific terms or were otherwise breached. It is
accordingly agreed that the parties shall be entitled to an injunction or
injunctions to prevent breaches of this Agreement and to enforce specifically
the terms and provisions of this Agreement in any federal court located in
Maryland or in any state court located in Maryland this being in addition to any
other remedy to which they are entitled at law or in equity. In addition, each
of the parties hereto (a) consents to submit itself (without making such
submission exclusive) to the personal jurisdiction of any federal court located
in Maryland or any state court located in Maryland in the event any dispute
arises out of this Agreement or any of the transactions contemplated by this
Agreement and (b) agrees that it will not attempt to deny or defeat such
personal jurisdiction by motion or other request for leave from any such court.

     8.9 Severability. Any term or provision of this Agreement which is invalid
or unenforceable in any jurisdiction shall, as to that jurisdiction, be
ineffective to the extent of such invalidity or unenforceability without
rendering invalid or unenforceable the remaining terms and provisions of this
Agreement or affecting the validity or enforceability of any of the terms or
provisions of this Agreement in any other jurisdiction. If any provision of this
Agreement is so broad as to be unenforceable, the provision shall be interpreted
to be only so broad as is enforceable.

     8.10 Exculpation. This Agreement shall not impose any personal liability on
any shareholder, trustee, trust manager, officer, employee or agent of EOP or
Cornerstone, and all Persons shall look solely to the property of EOP or
Cornerstone for the payment of any claim hereunder or for the performance of
this Agreement.

     8.11 Joint and Several Obligations. In each case where both Cornerstone and
Cornerstone Partnership, on the one hand, or EOP and EOP Partnership, on the
other hand, are obligated to perform the same obligation hereunder, such
obligation shall be joint and several.

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     IN WITNESS WHEREOF, EOP, EOP Partnership, Cornerstone and Cornerstone
Partnership have caused this Agreement to be signed by their respective officers
(or general partners) thereunto duly authorized all as of the date first written
above.

                                            EQUITY OFFICE PROPERTIES TRUST

                                            By:   /s/ TIMOTHY H. CALLAHAN
                                              ----------------------------------
                                                Name: Timothy H. Callahan
                                                Title: President

                                            EOP OPERATING LIMITED PARTNERSHIP

                                            By: Equity Office Properties Trust,
                                                its managing general partner

                                            By:   /s/ TIMOTHY H. CALLAHAN
                                              ----------------------------------
                                                Name: Timothy H. Callahan
                                                Title: President

                                            CORNERSTONE PROPERTIES INC.

                                            By:      /s/ JOHN S. MOODY
                                              ----------------------------------
                                                Name: John S. Moody
                                                Title: President & CEO

                                            CORNERSTONE PROPERTIES LIMITED
                                            PARTNERSHIP

                                            By: Cornerstone Properties Inc.,
                                                its sole general partner

                                            By:      /s/ JOHN S. MOODY
                                              ----------------------------------
                                                Name: John S. Moody
                                                Title: President & CEO

                                      A-58
<PAGE>   293

                                                                         ANNEX B

                          [LETTERHEAD OF J.P. MORGAN]

February 11, 2000

The Board of Trustees
Equity Office Properties Trust
Two N. Riverside Plaza
Chicago, IL 60606

Attention: Mr. Samuel Zell
           Chairman

Ladies and Gentlemen:

     You have requested our opinion as to the fairness, from a financial point
of view, to Equity Office Properties Trust ("EOP" or the "Company") of the
consideration proposed to be paid by the Company in connection with the proposed
merger (the "Merger") of Cornerstone Properties Inc. (the "Seller") with and
into the company. Pursuant to the Agreement and Plan of Merger, dated as of
February 11, 2000 (the "Agreement"), among the Company, the Seller, and their
operating partnership subsidiaries, the Seller will be merged with and into the
Company, with the Company as the survivor of such merger, and each share of
common stock, no par value, of the Seller will be converted into the right to
receive either $18.00 or 0.7009 common shares of beneficial interest, $.01 par
value, of the Company, or a combination of such cash and stock consideration
according to the election and proration provisions in the Agreement.

     In arriving at our opinion, we have reviewed (i) the Agreement; (ii)
certain publicly available information concerning the business of the Seller and
of certain other companies engaged in businesses comparable to those of the
Seller, and the reported market prices for certain other companies' securities
deemed comparable; (iii) publicly available terms of certain transactions
involving companies comparable to the Seller and the consideration received for
such companies; (iv) current and historical market prices of the common stock of
the Seller and the Company; (v) the audited financial statements of the Company
and the Seller for the fiscal year ended December 31, 1998, and the unaudited
financial statements of the Company and the Seller for the period ended
September 30, 1999; (vi) certain agreements with respect to outstanding
indebtedness or obligations of the Company and the Seller; (vii) certain
internal financial analyses and forecasts prepared by the Company and the Seller
and their respective managements; and (viii) the terms of other business
combinations that we deemed relevant.

     In addition, we have held discussions with certain members of the
management of the Company and the Seller with respect to certain aspects of the
Merger, and the past and current business operations of the Company and the
Seller, the financial condition and future prospects and operations of the
Company and the Seller, the effects of the Merger on the financial condition and
future prospects of the Company and the Seller, and certain other matters we
believed necessary or appropriate to our inquiry. We have reviewed such other
financial studies and analyses and considered such other information as we
deemed appropriate for the purposes of this opinion.

     In giving our opinion, we have relied upon and assumed, without independent
verification, the accuracy and completeness in all material respects of all
information that was publicly available or was furnished to us by the Company
and the Seller or otherwise reviewed by us, and we have not assumed any
responsibility or liability therefor. We have not conducted any valuation or
appraisal of any assets or liabilities, nor have any such valuations or
appraisals been provided to us. In relying on financial analyses and forecasts
provided to us, we have assumed that they have been reasonably prepared based on
assumptions reflecting the best currently available estimates and judgments by
management as to the expected future results of operations and financial
condition of the Company and the Seller to which such analyses or forecasts
relate. We have also assumed that the Merger will have the tax consequences

                                       B-1
<PAGE>   294

described in discussions with, and materials furnished to us by, representatives
of the Company, and that the other transactions contemplated by the Agreement
will be consummated as described in the Agreement. We have relied as to all
legal matters relevant to rendering our opinion upon the advice of counsel.

     Our opinion is necessarily based on economic, market and other conditions
as in effect on, and the information made available to us as of, the date
hereof. It should be understood that subsequent developments may affect this
opinion and that we do not have any obligation to update, revise, or reaffirm
this opinion. We are expressing no opinion herein as to the price at which the
Company's shares will trade at any future time.

     We have acted as financial advisor to the Company with respect to the
proposed Merger and will receive a fee from the Company for our services
performed to date. We will also receive an additional fee if the proposed Merger
is consummated. In the ordinary course of their businesses, our affiliates may
actively trade the debt and equity securities of the Company or the Seller for
their own account or for the accounts of customers and, accordingly, they may at
any time hold long or short positions in such securities.

     On the basis of and subject to the foregoing, it is our opinion as of the
date hereof that the consideration proposed to be paid by the Company in the
Merger is fair, from a financial point of view, to the Company.

     This letter is provided to the Board of Trustees of the Company in
connection with and for the purposes of its evaluation of the Merger. This
opinion does not constitute a recommendation to any shareholder of the Company
as to how such shareholder should vote with respect to the Merger. This opinion
may not be disclosed, referred to, or communicated (in whole or in part) to any
third party for any purpose whatsoever except with our prior written consent in
each instance. This opinion may be reproduced in full in any filing made by the
Company with the Securities and Exchange Commission in connection with the
Merger.

Very truly yours,

J.P. MORGAN SECURITIES INC.

By:       /s/ JOHN PERKINS
    --------------------------------
    Name: John Perkins
    Title: Vice President

                                       B-2
<PAGE>   295

                                                                         ANNEX C

                         [LETTERHEAD OF LAZARD FRERES]

                                                      February 11, 2000

The Board of Directors
Cornerstone Properties Inc.
126 East 56th Street
New York, NY

Dear Members of the Board:

     We understand that Cornerstone Properties Inc. ("Cornerstone") has entered
into an Agreement and Plan of Merger with Equity Office Properties Trust
("Equity Office") dated as of February 11, 2000 (the "Merger Agreement"),
pursuant to which Cornerstone will merge with and into Equity Office and
Cornerstone Properties Limited Partnership ("Cornerstone OP") will merge with
and into EOP Operating Limited Partnership ("Equity Office OP") (collectively,
the "Merger"). Pursuant to the Merger (as set out in the Merger Agreement), each
outstanding share of common stock of Cornerstone ("Common Stock") would be
converted into the right to receive either $18.00 in cash or .7009 shares of
Equity Office common stock as elected by the holders of Cornerstone Common
Stock, and subject to pro ration and adjustment as provided in the Merger
Agreement.

     You have requested our opinion as to the fairness, from a financial point
of view, to the holders of Common Stock of the consideration to be received by
such holders in the Merger. In connection with this opinion, we have:

          (i) Reviewed the financial terms and conditions of the Merger
     Agreement;

          (ii) Analyzed certain historical business and financial information
     relating to Cornerstone and Equity Office;

          (iii) Reviewed various financial forecasts and other data provided to
     us by each of Cornerstone and Equity Office and relating to their
     respective businesses;

          (iv) Held discussions with members of the senior management of
     Cornerstone and Equity Office with respect to the businesses, prospects and
     strategic objectives of each company;

          (v) Reviewed public information with respect to certain other
     companies in lines of business we believe to be generally comparable to the
     business of Cornerstone;

          (vi) Reviewed the financial terms of certain business combinations
     involving companies in lines of business we believe to be generally
     comparable to those of Cornerstone;

          (vii) Reviewed the historical stock prices and trading volumes of the
     Common Stock and the common stock of Equity Office; and

          (viii) Conducted such other financial studies, analyses and
     investigations as we deemed appropriate.

     We have relied upon the accuracy and completeness of the foregoing
information, and have not assumed any responsibility for any independent
verification of such information or any independent valuation or appraisal of
any of the assets or liabilities of Cornerstone or Equity Office, or concerning
the solvency or fair value of Cornerstone, Cornerstone OP, Equity Office, Equity
Office OP or any other entity. With respect to financial forecasts, we have
assumed that they have been reasonably prepared on bases reflecting the best
currently available estimates and judgments of management of Cornerstone and
Equity Office as to the future financial performance of Cornerstone and Equity
Office, respectively. We

                                       C-1
<PAGE>   296

assume no responsibility for and express no view as to such forecasts or the
assumptions on which they are based.

     Further, our opinion is necessarily based on economic, monetary, market and
other conditions as in effect on, and the information made available to us as of
the date hereof. As you know, we have not been asked to solicit nor have we
solicited indications of interest from any other parties.

     In rendering our opinion, we have assumed that the Merger will be
consummated on the terms described in the Merger Agreement, without any waiver
of any material terms or conditions by Cornerstone or Cornerstone OP, and that
obtaining the necessary regulatory approvals for the Merger will not have an
adverse effect on Cornerstone or Cornerstone OP. We note that Cornerstone OP
unitholders have an option, exercisable prior to the Merger, to receive Equity
Office OP Units to be issued in the partnership merger or to redeem their units
for shares of Cornerstone Common Stock and elect to receive cash in the Merger
of Cornerstone into Equity Office, with respect to which we do not express a
view. However, our analysis has assumed that prior to the Merger each holder of
units in Cornerstone OP has elected to exercise its redemption right and receive
shares of Common Stock in Cornerstone in exchange therefor in the manner
provided in the Merger Agreement.

     Lazard Freres & Co. LLC is acting as investment banker to Cornerstone in
connection with the Merger and will receive a fee for our services paid partly
upon announcement and the balance upon the closing of the Merger. We have in the
past provided investment banking services to Cornerstone for which we have
received customary fees.

     Our engagement and the opinion expressed herein are for the benefit of
Cornerstone's Board of Directors and our opinion does not constitute a
recommendation as to how the holders of Common Stock of Cornerstone (and the
holders of limited partnership interests in Cornerstone OP) should vote with
respect to the matters contemplated by the Merger Agreement. Except as provided
in the engagement letter dated January 28, 2000, between Cornerstone and us, it
is understood that this letter may not be disclosed or otherwise referred to
without our prior consent, except as may otherwise be required by law or by a
court of competent jurisdiction.

     Based on and subject to the foregoing, we are of the opinion that the
consideration to be received in the Merger as set forth above is fair, from a
financial point of view, to the holders of Common Stock of Cornerstone.

                                            Very truly yours,

                                            LAZARD FRERES & CO. LLC

                                            By    /s/ MATTHEW J. LUSTIG
                                            ------------------------------------
                                                     Matthew J. Lustig
                                                     Managing Director

                                       C-2
<PAGE>   297

                                                                         ANNEX D

                AMENDMENTS TO EQUITY OFFICE DECLARATION OF TRUST
               RELATING TO "DOMESTICALLY-CONTROLLED" REIT STATUS

1. AMENDMENT TO SECTION 7.2.1(a)

     Section 7.2.1(a) is amended to add the following new subparagraph (iv):

          (iv) No Person shall acquire Beneficial Ownership of any Shares after
     the Effective Time if, as a result of such acquisition of Beneficial
     Ownership, the fair market value of the Shares owned directly and
     indirectly by Non-U.S. Persons for purposes of Section 897(h)(4)(B) of the
     Code would comprise forty three percent (43%) or more of the fair market
     value of the issued and outstanding Shares; provided, however, that the
     foregoing shall not apply to any acquisition of Beneficial Ownership of any
     Preferred Shares outstanding at the Effective Time or any Common Shares
     upon the conversion of any such Preferred Shares.

2. AMENDMENTS TO SECTION 7.1

     Section 7.1 is amended to add the following new definitions:

          Effective Time.  The term "Effective Time" shall mean the later of (i)
     the time the SDAT accepts for record articles of merger relating to the
     merger of Cornerstone Properties, Inc. with and into the Trust or (ii) the
     time established under such articles, not to exceed 30 days after the
     articles are accepted for record by the SDAT.

          Non-U.S. Person.  The term "Non-U.S. Person" shall mean a Person other
     than a U.S. Person.

          U.S. Person.  The term "U.S. Person" shall mean (a) a citizen or
     resident of the United States, (b) a partnership created or organized in
     the United States or under the laws of the United States or any state
     therein (including the District of Columbia), (c) a corporation created or
     organized in the United States or under the laws of the United States or
     any state therein (including the District of Columbia), and (d) any estate
     or trust (other than a foreign estate or foreign trust, within the meaning
     of Section 7701(a)(31) of the Code).

3. AMENDMENTS TO SECTION 7.2.1(b)

     Section 7.2.1(b) is amended to read as follows:

          (b) Transfer in Trust.  If any Transfer of Shares (whether or not such
     Transfer is the result of transaction entered into through the facilities
     of the NYSE or any other national securities exchange or automated
     inter-dealer quotation system) occurs which, if effective, would result in
     any Person Beneficially Owning or Constructively Owning Shares in violation
     of Section 7.2.1(a)(i), (ii) or (iv),

             (i) then that number of Shares the Beneficial or Constructive
        Ownership of which otherwise would cause such Person to violate Section
        7.2.1(a)(i), (ii) or (iv), as applicable (rounded up to the nearest
        whole share) shall be automatically transferred to a Charitable Trust
        for the benefit of a Charitable Beneficiary, as described in Section
        7.3, effective as of the close of business on the Business Day prior to
        the date of such Transfer, and such Person shall acquire no rights in
        such Shares; or

             (ii) if the transfer to the Charitable Trust described in clause
        (i) of this sentence would not be effective for any reason to prevent
        the violation of Section 7.2.1(a)(i), (ii) or (iv), as applicable, then
        the Transfer of that number of Shares that otherwise would cause such
        Person to violate Section 7.2.1(a)(i), (ii) or (iv), as applicable
        (rounded up to the nearest whole share) shall be void ab initio, and the
        intended transferee shall acquire no rights in such Shares.

                                       D-1
<PAGE>   298

4. AMENDMENT TO SECTION 7.2.4(b)

     The existing Section 7.2.4(b) is amended to read as follows:

          (b) each Person who is a Beneficial or Constructive Owner of Shares
     and each Person (including the shareholder of record) who is holding Shares
     for a Beneficial or Constructive Owner shall provide to the Trust such
     information as the Trust may require, in good faith, in order to determine
     the Trust's status as a REIT or a "domestically controlled REIT" (within
     the meaning of Section 897(h)(4)(B) of the Code) and to comply with the
     requirements of any taxing authority or to determine such compliance.

5. AMENDMENT TO ADD NEW SECTION 7.2.9

     The existing Section 7.2.9 is renumbered as Section 7.2.10 and the
following new Section 7.2.9 is added:

          Section 7.2.9 Increase in Percentage Set Forth in Section
     7.2.1(a)(iv).  The Board of Trustees may from time to time increase the
     percentage set forth in Section 7.2.1(a)(iv) from forty three percent (43%)
     to such higher percentage as shall be determined by the Board of Trustees;
     provided, however, that in no event shall such percentage exceed forty nine
     percent (49%) less the percentage of the aggregate fair market value of the
     total issued and outstanding Shares represented by the fair market value of
     any Preferred Shares then outstanding that were outstanding at the
     Effective Time (as such fair market values are determined by the Board of
     Trustees in good faith).

6. AMENDMENTS TO SECTION 7.2.10

     The first sentence of the legend set forth in Section 7.2.10 (as renumbered
pursuant to the other amendments made pursuant hereto) is amended to delete the
word "and" immediately preceding the following: "(iv) no Person may Transfer
Shares . . .", and to insert the following new language at the end of such first
sentence:

          ; and (v) no Person may acquire Beneficial Ownership of any Shares
     after the Effective Date if, as a result of such acquisition, the fair
     market value of the Shares owned directly and indirectly by Non-U.S.
     Persons would comprise more than forty three percent (43%) of the fair
     market value of the issued and outstanding Shares; provided, however, that
     clause (v) shall not apply to any acquisition of any Preferred Shares
     outstanding at the Effective Time.

                                       D-2
<PAGE>   299

                                    PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 20.  INDEMNIFICATION OF DIRECTORS AND OFFICERS

  EQUITY OFFICE PROPERTIES TRUST:

     Title 8 of the Corporations and Associations Article of the Annotated Code
of Maryland, as amended from time to time (the "Maryland REIT Law"), permits a
Maryland REIT to include in its declaration of trust a provision limiting the
liability of its trustees and officers to the trust and its shareholders for
money damages except for liability resulting from (a) actual receipt of an
improper benefit or profit in money, property or services or (b) active and
deliberate dishonesty established by a final judgment as being material to the
cause of action. The Equity Office declaration of trust contains such a
provision which eliminates such liability to the maximum extent permitted by the
Maryland REIT law.

     The Equity Office declaration of trust authorizes Equity Office, to the
maximum extent permitted by Maryland law, to obligate itself to indemnify and to
pay or reimburse reasonable expenses in advance of final disposition of a
proceeding to (a) any present or former trustee or officer or (b) any individual
who, while a trustee of Equity Office and at the request of Equity Office,
serves or has served as a director, officer, partner, trustee, employee or agent
of another corporation, partnership, joint venture, trust, employee benefit plan
or any other enterprise from and against any claim or liability to which such
person may become subject or which such person may incur by reason of his or her
status as a present or former trustee or officer of Equity Office. The Equity
Office bylaws obligate Equity Office, to the maximum extent permitted by
Maryland law, to indemnify and to pay or reimburse reasonable expenses in
advance of final disposition of a proceeding to (a) any present or former
trustee or officer who is made party to the proceeding by reason of his service
in that capacity or (b) any individual who, while a trustee or officer of Equity
Office and at the request of Equity Office, serves or has served another
corporation, partnership, joint venture, trust, employee benefit plan or any
other enterprise as a trustee, director, officer or partner of such corporation,
partnership, joint venture, trust, employee benefit plan or other enterprise and
who is made a party to the proceeding by reason of his service in that capacity,
against any claim or liability to which he or she may become subject by reason
of such status. The Equity Office declaration of trust and bylaws also permit
Equity Office to indemnify and advance expenses to any person who served a
predecessor of Equity Office in any of the capacities described above and to any
employee or agent of or a predecessor of Equity Office. The Equity Office bylaws
require Equity Office to indemnify a trustee or officer, or any former trustee
or officer, who has been successful, on the merits or otherwise, in the defense
of any proceeding to which he or she is made a party by reason of his service in
that capacity against reasonable expenses incurred in connection with the
proceeding.

     The Maryland REIT Law permits a Maryland REIT to indemnify and advance
expenses to its trustees, officers, employees and agents to the same extent as
permitted by the Maryland General Corporation Law, as amended from time to time
(the "MGCL"), for directors and officers of Maryland corporations. The MGCL
permits a corporation to indemnify its present and former directors and
officers, among others, against judgments, penalties, fines, settlements and
reasonable expenses actually incurred by them in connection with any proceeding
to which they may be made a party by reason of their service in those or other
capacities unless it is established that (a) the act or omission of the director
or officer was material to the matter giving rise to the proceeding and (x) was
committed in bad faith or (y) was the result of active and deliberate
dishonesty, (b) the director or officer actually received an improper personal
benefit in money, property or services or (c) in the case of any criminal
proceeding, the director or officer had reasonable cause to believe that the act
or omission was unlawful. The foregoing limitations on indemnification are
expressly set forth in the Equity Office bylaws. However, under the MGCL, a
Maryland corporation may not indemnify for any adverse judgment in a suit by or
in the right of the corporation or for a judgment of liability on the basis that
a personal benefit was improperly received, unless, in either case, a court
orders indemnification and then only for expenses. Under the MGCL, as a
condition to advancing expenses, as required by the Equity Office bylaws, Equity
Office must first receive

                                      II-1
<PAGE>   300

(a) a written affirmation by the trustee or officer of his good faith belief
that he or she has met the standard of conduct necessary for indemnification by
Equity Office and (b) a written undertaking by or on his behalf to repay the
amount paid or reimbursed by Equity Office if it shall ultimately be determined
that the standard of conduct was not met. In addition, Mr. Dobrowski, a trustee
of Equity Office, is indemnified by General Motors Investment Management
Corporation and will be covered by an insurance policy maintained by General
Motors Corporation, of which General Motors Investment Management Corporation is
a subsidiary, in connection with serving on the Equity Office board of trustees.

     The limited partnership agreement of EOP Operating Limited Partnership also
provides for indemnification of Equity Office and its officers and trustees to
the same extent that indemnification is provided to officers and trustees of
Equity Office in its declaration of trust, and limits the liability of Equity
Office and its officers and trustees to EOP Partnership and its respective
partners to the same extent that the Equity Office declaration of trust limits
the liability of the officers and trustees of Equity Office to Equity Office and
its shareholders.

  EOP OPERATING LIMITED PARTNERSHIP:

     Pursuant to its Agreement of Limited Partnership, EOP Partnership is
obligated to indemnify, to the fullest extent provided by law, any person or
entity made a party to a proceeding by reason of its status as a general partner
or a limited partner of EOP Partnership or a trustee, director or officer of any
general partner and such other persons or entities as the Trust may designate
from time to time in its sole discretion (an "Indemnitee") from and against any
and all losses, claims, damages, liabilities, joint or several, expenses
(including without limitation, attorneys fees and other legal fees and
expenses), judgments, fines, settlements and other amounts arising from or in
connection with any and all claims, demands, actions, suits or proceedings,
civil, criminal, administrative or investigative, incurred by the Indemnitee and
relating to EOP Partnership or the general partners or the operation of, or the
ownership of property by, any of them as set forth in the Partnership Agreement
in which any such Indemnitee may be involved, or is threatened to be involved,
as a party or otherwise, unless it is established by a final determination of a
court of competent jurisdiction that: (a) the act or omission of the Indemnitee
was material to the matter giving rise to the proceeding and either was
committed in bad faith or was the result of active and deliberate dishonesty,
(b) the Indemnitee actually received an improper personal benefit in money,
property or services or (c) in the case of any criminal proceeding, the
Indemnitee had reasonable cause to believe that the act or omission was
unlawful. Any indemnification shall be made only out of the assets of EOP
Partnership, and any insurance proceeds from the liability policy covering the
general partners and any Indemnitee, and neither a general partner nor any
limited partner shall have any obligation to contribute to the capital of EOP
Partnership or otherwise provide funds to enable EOP Partnership to fund its
indemnity obligations. EOP Partnership is obligated to advance amounts to an
Indemnitee for expenses upon receipt of (a) a written affirmation of the
Indemnitee that it believes it has met the standard of conduct necessary to
entitle it to indemnification and (b) a written undertaking of the Indemnitee
that it will repay any such advances if it shall be ultimately determined that
it did not meet such standard of conduct. The foregoing indemnification rights
are in addition to any other rights afforded to an Indemnitee under any other
agreement, by vote of the partners, under applicable law or otherwise, and shall
continue as to an Indemnitee who has ceased to serve in such capacity unless
otherwise provided in a written agreement pursuant to which such Indemnitees are
indemnified. EOP Partnership is authorized to purchase and maintain insurance on
behalf of the Indemnitees with respect to the foregoing matters. EOP Partnership
shall be deemed to have requested an Indemnitee to serve as fiduciary of an
employee benefit plan whenever the performance by it of its duties to EOP
Partnership also imposes duties on, or otherwise involves services by, it to the
plan or participants or beneficiaries of the plan; excise taxes assessed on an
Indemnitee with respect to an employee benefit plan pursuant to applicable law
shall constitute fines; and actions taken or omitted by the Indemnitee with
respect to an employee benefit plan in the performance of its duties for a
purpose reasonably believed by it to be in the interest of the participants and
beneficiaries of the plan shall be deemed to be for a purpose which is not
opposed to the best interests of EOP Partnership. An Indemnitee shall not be
denied indemnification in whole or in part

                                      II-2
<PAGE>   301

because the Indemnitee had an interest in the transaction with respect to which
the indemnification applies if the transaction was otherwise permitted by the
terms of the Partnership Agreement.

     Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to trustees, officers, partners, or persons controlling Equity
Office or EOP Partnership under the foregoing provisions, Equity Office and EOP
Partnership have been informed that in the opinion of the SEC such
indemnification is against public policy as expressed in the Act and is
therefore unenforceable.

  CORNERSTONE PROPERTIES INC.:

     Section 78.7502 of Chapter 78 of the Nevada Revised Statutes (the "NRS")
empowers a corporation to indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action or
suit or proceeding, whether civil, criminal, administrative or investigative
(other than an action by or in the right of the corporation) by reason of the
fact that he is or was a director, officer, employee or agent of the corporation
or is or was serving at the request of the corporation as a director, officer,
employee or agent of another corporation or other enterprise, against expenses
(including attorneys' fees), judgments, fines and amounts paid in settlement
actually and reasonably incurred by him in connection with such action, suit or
proceeding if he acted in good faith and in a manner he reasonably believed to
be in or not opposed to the best interests of the corporation, and with respect
to any criminal action or proceeding, had no reasonable cause to believe his
conduct was unlawful. The termination of any action, suit or proceeding by
judgment, order, settlement or conviction or upon a plea of NOLO CONTENDERE or
its equivalent does not, of itself, create a presumption that the person did not
act in good faith or in a manner which he reasonably believed to be in or not
opposed to the best interests of the corporation or that, with respect to any
criminal action or proceeding, he had reasonable cause to believe his actions
were unlawful.

     Section 78.7502 of the NRS empowers a corporation to indemnify any person
who was or is a party or is threatened to be made a party to any threatened,
pending or completed action or suit by or in the right of the corporation to
procure a judgment in its favor by reason of the fact that such person acted in
any of the capacities set forth above against expenses, including attorneys'
fees, actually and reasonably incurred by him in connection with the defense or
settlement of such action or suit if he acted under similar standards to those
described above expect that no indemnification may be made in respect of any
claim, issue or matter as to which such person shall have been adjudged to be
liable to the corporation or for amounts paid in settlement to the corporation
unless and only to the extent that the court in which such action or suit was
brought determines that, despite the adjudication of liability, such person is
fairly and reasonably entitled to indemnity for such expenses as the court deems
proper.

     Section 78.7502 of the NRS further provides that to the extent a director
or officer of a corporation has been successful in the defense of any action,
suitor proceeding referred to in subsections (1) and (2) or in the defense of
any claim, issue or matter therein, he shall be indemnified against expenses
(including attorneys' fees) actually and reasonably incurred by him in
connection therewith. Section 78.751 of the NRS provides that any
indemnification provided for by section 78.7502 of the NRS (by court order or
otherwise) shall not be deemed exclusive of any other rights to which the
indemnified party may be entitled and that the scope of indemnification shall
continue as to directors, officers, employees or agents who have ceased to hold
such positions, and to their heirs, executors and administrators. Section 78.752
empowers the corporation to purchase and maintain insurance on behalf of a
director, officer, employee or agent of the corporation against any liability
asserted against him or incurred by him in any such capacity or arising out of
his status as such whether or not the corporation would have the power to
indemnify him against such liabilities under section 78.7502.

     Article IX of Cornerstone's bylaws provides for indemnification of its
officers and directors, substantially identical in scope to that permitted under
section 78.7502 of the NRS. The Cornerstone bylaws provide, pursuant to
Subsection 2 of section 78.7502 of the NRS, that the expenses of officers and
directors incurred in defending any action, suit or proceeding, whether civil,
criminal, administrative or investigative, must be paid by Cornerstone as they
are incurred and in advance of the final disposition of

                                      II-3
<PAGE>   302

the action, suit or proceeding, upon receipt of any undertaking by or on behalf
of the director or officer to repay such amounts unless it shall ultimately be
determined that he is entitled to be indemnified by Cornerstone pursuant to
Article IX of the bylaws.

ITEM 21.  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

     (a) Exhibits

<TABLE>
<CAPTION>
EXHIBIT NO                        EXHIBIT DESCRIPTION
- ----------                        -------------------
<C>           <S>
    2.1       Agreement and Plan of Merger, dated as of February 11, 2000,
              among Equity Office, EOP Partnership, Cornerstone and
              Cornerstone Partnership (included in this Registration
              Statement as Annex A to the Consent Solicitation/Information
              Statement/Prospectus)
    5.1 *     Opinion of Hogan & Hartson L.L.P. regarding the legality of
              the securities being registered on behalf of EOP and EOP
              Partnership
    5.2 *     Opinion of Lionel, Sawyer & Collins regarding the legality
              of the securities being registered on behalf of Cornerstone
    8.1 *     Opinion of Hogan & Hartson L.L.P. regarding the
              qualification of the REIT merger as a reorganization for
              federal income tax purposes and related federal income tax
              consequences
    8.2 *     Opinion of King & Spalding regarding the qualification of
              the REIT merger as a reorganization for federal income tax
              purposes and related federal income tax consequences
    8.3 *     Opinion of Hogan & Hartson L.L.P. regarding the
              qualification by Equity Office Properties Trust as a real
              estate investment trust and EOP Operating Limited
              Partnership as a partnership for federal income tax purposes
    8.4 *     Opinion of King & Spalding regarding the qualification of
              Cornerstone Properties Inc. as a real estate investment
              trust and Cornerstone Properties Limited Partnership as a
              partnership for federal income tax purposes
   23.1       Consent of Ernst & Young LLP (EOP and EOP Partnership)
   23.2       Consent of PricewaterhouseCoopers LLP (Cornerstone and
              Cornerstone Partnership)
   23.3 *     Consent of Hogan & Hartson L.L.P. (included in Exhibit 5.1)
   23.4 *     Consent of Lionel, Sawyer & Collins (included in Exhibit
              5.2)
   23.5 *     Consent of Hogan & Hartson L.L.P. (included in Exhibits 8.1
              and 8.3)
   23.6 *     Consent of King & Spalding (included in Exhibits 8.2 and
              8.4)
   23.7       Consent of J.P. Morgan Securities Inc.
   23.8       Consent of Lazard Freres & Co. LLC
   23.9       Consent of William Wilson III to be named as a trustee
   23.10      Consent of John S. Moody to be named as a trustee
   23.11      Consent of Jan H.W.R van der Vlist to be named as a trustee
   24.1       Equity Office Properties Trust power of attorney (included
              on Equity Office Properties Trust signature page)
   24.2       EOP Operating Limited Partnership power of attorney
              (included on EOP Operating Limited Partnership signature
              page)
   24.3       Cornerstone Properties Inc. power of attorney (included on
              Cornerstone Properties Inc. signature page)
   99.1       Stock Option Agreement, dated February 11, 2000, by and
              among Cornerstone, Equity Office, Deutsche Bank AG and
              Deutscher Herold Lebensversicherungs-AG (incorporated by
              reference to Exhibit 10.1 of Equity Office's Form 8-K dated
              February 16, 2000)
</TABLE>

                                      II-4
<PAGE>   303

<TABLE>
<CAPTION>
EXHIBIT NO                        EXHIBIT DESCRIPTION
- ----------                        -------------------
<C>           <S>
   99.2       Voting Agreement, dated February 11, 2000, by and among
              Equity Office, EOP Operating Limited Partnership, WCP
              Services, Inc. and Stichting Pensioenfonds voor de
              Gezondheid, Geotelijke en Maatschappelijke Belagen
              (incorporated by reference to Exhibit 10.2 of Equity
              Office's Form 8-K dated February 16, 2000)
   99.3 *     Cornerstone Partnership -- Form of Consent
   99.4 *     Form of Redemption/Notice of Election
</TABLE>

- ---------------
* To be filed by amendment.

     (b) Financial Statement Schedules

     The following financial statement schedule was filed with the EOP
Partnership Annual Report on Form 10-K for the year ended December 31, 1999
(File no. 1-13625), filed with the SEC on March 30, 2000, and is incorporated
herein by reference:

        Schedule III -- Real Estate and Accumulated Depreciation

     Schedules not listed above have been omitted because they are inapplicable
or the information required to be set forth therein is contained, or
incorporated by reference, in the consolidated final statements of Equity Office
or notes thereto.

ITEM 22.  UNDERTAKINGS

     Equity Office Properties Trust, EOP Operating Limited Partnership and
Cornerstone Properties Inc., as applicable, hereby undertake:

          1. To file, during any period in which offers or sales are being made,
     a post-effective amendment to this registration statement:

             (i) to include any prospectus required by section 10(a)(3) of the
        Securities Act of 1933;

             (ii) to reflect in the prospectus any facts or events arising after
        the effective date of the registration statement (or the most recent
        post-effective amendment thereof) which, individually or in the
        aggregate, represent a fundamental change in the information set forth
        in the registration statement. Notwithstanding the foregoing, any
        increase or decrease in volume of securities offered (if the total
        dollar value of securities offered would not exceed that which was
        registered) and any deviation from the low or high end of the estimated
        maximum offering range may be reflected in the form of prospectus filed
        with the Commission pursuant to rule 424(b) if, in the aggregate, such
        changes in volume and price represent no more than a 20% change in the
        maximum aggregated offering price set forth in the "Calculation of
        Registration Fee" table in the effective registration statement;

             (iii) to include any material information with respect to the plan
        of distribution not previously disclosed in the registration statement
        or any material change to such information in the registration
        statement.

          2. That, for the purpose of determining any liability under the
     Securities Act of 1933, each such post-effective amendment shall be deemed
     to be a new registration statement relating to the securities offered
     therein, and the offering of such securities at that time shall be deemed
     to be the initial bona fide offering thereof.

          3. To remove from registration by means of a post-effective amendment
     any of the securities being registered which remain unsold at the
     termination of the offering.

          4. That, for the purpose of determining any liability under the
     Securities Act of 1933, each filing of the respective registrant's annual
     reports pursuant to section 13(a) or section 15(d) of the Securities
     Exchange Act of 1934 (and, where applicable, each filing of an employee
     benefit plan's annual report pursuant to section 15(d) of the Securities
     Exchange Act of 1934) that is incorporated

                                      II-5
<PAGE>   304

     by reference in the registration statement shall be deemed to be a new
     registration statement relating to the securities offered therein, and the
     offering of such securities at that time shall be deemed to be the initial
     bona fide offering thereof.

          5. That before any public reoffering of the securities registered
     hereunder through use of a prospectus which is a part of this registration
     statement, by any person or party who is deemed to be an underwriter within
     the meaning of rule 145(c), the applicable issuer undertakes that such
     reoffering prospectus will contain the information called for by the
     applicable registration form with respect to reofferings by persons who may
     be deemed underwriters, in addition to the information called for by the
     other items of the applicable form.

          6. That every prospectus: (i) that is filed pursuant to paragraph (5)
     immediately preceding, or (ii) that purports to meet the requirements of
     section 10(a)(3) of the Act and is used in connection with an offering of
     securities subject to rule 415, will be filed as a part of an amendment to
     the registration statement and will not be used until such amendment is
     effective, and that, for purposes of determining any liability under the
     Securities Act of 1933, each such post-effective amendment shall be deemed
     to be a new registration statement relating to the securities offered
     therein, and the offering of such securities at that time shall be deemed
     to be the initial bona fide offering thereof.

          7. Insofar as indemnification for liabilities arising under the
     Securities Act of 1933 may be permitted to trustees, officers and
     controlling persons of the registrant pursuant to the foregoing provisions,
     or otherwise, the registrant has been advised that in the opinion of the
     Securities and Exchange Commission such indemnification is against public
     policy as expressed in the Act and is, therefore, unenforceable. In the
     event that a claim for indemnification against such liabilities, other than
     the payment by the registrant of expenses incurred or paid by a trustee,
     officer or controlling person of the registrant in the successful defense
     of any action, suit or proceeding, is asserted by such trustee, officer or
     controlling person in connection with the securities being registered, the
     registrant will, unless in the opinion of its counsel the matter has been
     settled by controlling precedent, submit to a court of appropriate
     jurisdiction the question whether such indemnification by it is against
     public policy as expressed in the Act and will be governed by the final
     adjudication of such issue.

          8. To respond to requests for information that is incorporated by
     reference into the prospectus pursuant to Item 4, 10(b), 11, or 13 of this
     form, within one business day of receipt of such request, and to send the
     incorporated documents by first class mail or other equally prompt means.
     This includes information contained in documents filed subsequent to the
     effective date of the registration statement through the date of responding
     to the request.

          9. To supply by means of a post-effective amendment all information
     concerning a transaction, and the company being acquired involved therein,
     that was not the subject of and included in the registration statement when
     it became effective.

                                      II-6
<PAGE>   305

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act, the registrant has duly
caused this registration statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Chicago, State of
Illinois on April 25, 2000.

                                          EQUITY OFFICE PROPERTIES TRUST

                                          By:    /s/ TIMOTHY H. CALLAHAN
                                            ------------------------------------
                                                    TIMOTHY H. CALLAHAN
                                               PRESIDENT AND CHIEF EXECUTIVE
                                                           OFFICER

     We, the undersigned trustees and officers of Equity Office Properties
Trust, do hereby constitute and appoint Timothy H. Callahan and Stanley M.
Stevens, and each and either of them, our true and lawful attorneys-in-fact and
agents, to do any and all acts and things in our name and our behalf in our
capacities as trustees and officers and to execute any and all instruments for
us and in our name in the capacities indicated below, which said attorneys and
agents, or either of them, may deem necessary or advisable to enable said Trust
to comply with the Securities Act of 1933 and any rules, regulations and
requirements of the Securities and Exchange Commission, in connection with this
registration statement, including specifically, but without limitation, any and
all amendments, including post-effective amendments, hereto; and we hereby
ratify and confirm all that said attorneys and agents, or either of them, shall
do or cause to be done by virtue thereof.

     Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed by the following persons in the
capacities indicated as of the 25th day of April, 2000.

<TABLE>
<CAPTION>
                      SIGNATURE                                                TITLE
                      ---------                                                -----
<C>                                                         <S>
               /s/ TIMOTHY H. CALLAHAN                      President, Chief Executive Officer and
- -----------------------------------------------------         Trustee (principal executive officer)
                 TIMOTHY H. CALLAHAN

               /s/ RICHARD D. KINCAID                       Chief Financial Officer (principal financial
- -----------------------------------------------------         officer and principal accounting officer)
                 RICHARD D. KINCAID

                   /s/ SAMUEL ZELL                          Chairman of the Board of Trustees
- -----------------------------------------------------
                     SAMUEL ZELL

               /s/ SHELI Z. ROSENBERG                       Trustee
- -----------------------------------------------------
                 SHELI Z. ROSENBERG

               /s/ THOMAS E. DOBROWSKI                      Trustee
- -----------------------------------------------------
                 THOMAS E. DOBROWSKI

              /s/ JAMES D. HARPER, JR.                      Trustee
- -----------------------------------------------------
                JAMES D. HARPER, JR.

               /s/ JERRY M. REINSDORF                       Trustee
- -----------------------------------------------------
                 JERRY M. REINSDORF
</TABLE>

                                      II-7
<PAGE>   306

<TABLE>
<CAPTION>
                      SIGNATURE                                                TITLE
                      ---------                                                -----
<C>                                                         <S>
               /s/ WILLIAM M. GOODYEAR                      Trustee
- -----------------------------------------------------
                 WILLIAM M. GOODYEAR

                 /s/ DAVID K. MCKOWN                        Trustee
- -----------------------------------------------------
                   DAVID K. MCKOWN

                 /s/ H. JON RUNSTAD                         Trustee
- -----------------------------------------------------
                   H. JON RUNSTAD

                 /s/ EDWIN N. SIDMAN                        Trustee
- -----------------------------------------------------
                   EDWIN N. SIDMAN

               /s/ D. J. ANDRE DE BOCK                      Trustee
- -----------------------------------------------------
                 D. J. ANDRE DE BOCK
</TABLE>

                                      II-8
<PAGE>   307

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act, the registrant has duly
caused this registration statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Chicago, State of
Illinois on April 25, 2000.

                                          EOP OPERATING LIMITED PARTNERSHIP

                                          By:  Equity Office Properties Trust,
                                          as Managing General Partner

                                          By:    /s/ TIMOTHY H. CALLAHAN
                                            ------------------------------------
                                                    TIMOTHY H. CALLAHAN
                                               PRESIDENT AND CHIEF EXECUTIVE
                                                           OFFICER

     We, the undersigned trustees of Equity Office Properties Trust, the
managing general partner of EOP Operating Limited Partnership, do hereby
constitute and appoint Timothy H. Callahan and Stanley M. Stevens, and each and
either of them, our true and lawful attorneys-in-fact and agents, to do any and
all acts and things in our name and our behalf in our capacities as trustees and
officers and to execute any and all instruments for us and in our name in the
capacities indicated below, which said attorneys and agents, or either of them,
may deem necessary or advisable to enable said Partnership to comply with the
Securities Act of 1933 and any rules, regulations and requirements of the
Securities and Exchange Commission, in connection with this registration
statement, including specifically, but without limitation, any and all
amendments, including post-effective amendments, hereto; and we hereby ratify
and confirm all that said attorneys and agents, or either of them, shall do or
cause to be done by virtue thereof.

     Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed by the following persons in the
capacities indicated as of the 25th day of April, 2000.

<TABLE>
<CAPTION>
                      SIGNATURE                                                TITLE
                      ---------                                                -----
<C>                                                         <S>
                   /s/ SAMUEL ZELL                          Chairman of the Board of Trustees
- -----------------------------------------------------
                     SAMUEL ZELL

               /s/ TIMOTHY H. CALLAHAN                      Trustee
- -----------------------------------------------------
                 TIMOTHY H. CALLAHAN

               /s/ SHELI Z. ROSENBERG                       Trustee
- -----------------------------------------------------
                 SHELI Z. ROSENBERG

               /s/ THOMAS E. DOBROWSKI                      Trustee
- -----------------------------------------------------
                 THOMAS E. DOBROWSKI

              /s/ JAMES D. HARPER, JR.                      Trustee
- -----------------------------------------------------
                JAMES D. HARPER, JR.

               /s/ JERRY M. REINSDORF                       Trustee
- -----------------------------------------------------
                 JERRY M. REINSDORF
</TABLE>

                                      II-9
<PAGE>   308

<TABLE>
<CAPTION>
                      SIGNATURE                                                TITLE
                      ---------                                                -----
<C>                                                         <S>
               /s/ WILLIAM M. GOODYEAR                      Trustee
- -----------------------------------------------------
                 WILLIAM M. GOODYEAR

                 /s/ DAVID K. MCKOWN                        Trustee
- -----------------------------------------------------
                   DAVID K. MCKOWN

                 /s/ H. JON RUNSTAD                         Trustee
- -----------------------------------------------------
                   H. JON RUNSTAD

                 /s/ EDWIN N. SIDMAN                        Trustee
- -----------------------------------------------------
                   EDWIN N. SIDMAN

               /s/ D. J. ANDRE DE BOCK                      Trustee
- -----------------------------------------------------
                 D. J. ANDRE DE BOCK
</TABLE>

                                      II-10
<PAGE>   309

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act, the registrant has duly
caused this registration statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of New York, State of New
York on April 25, 2000.

                                          CORNERSTONE PROPERTIES INC.

                                          By:       /s/ JOHN S. MOODY
                                            ------------------------------------
                                                       JOHN S. MOODY
                                                CHIEF EXECUTIVE OFFICER AND
                                                          PRESIDENT

     We, the undersigned directors and officers of Cornerstone Properties Inc.,
do hereby constitute and appoint John S. Moody and Rodney C. Dimock, and each
and either of them, our true and lawful attorneys-in-fact and agents, to do any
and all acts and things in our name and our behalf in our capacities as trustees
and officers and to execute any and all instruments for us and in our name in
the capacities indicated below, which said attorneys and agents, or either of
them, may deem necessary or advisable to enable said Trust to comply with the
Securities Act of 1933 and any rules, regulations and requirements of the
Securities and Exchange Commission, in connection with this registration
statement, including specifically, but without limitation, any and all
amendments, including post-effective amendments, hereto; and we hereby ratify
and confirm all that said attorneys and agents, or either of them, shall do or
cause to be done by virtue thereof.

     Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed by the following persons in the
capacities indicated as of the 25th day of April, 2000.

<TABLE>
<CAPTION>
                      SIGNATURE                                                TITLE
                      ---------                                                -----
<C>                                                         <S>

                                                            Chairman of the Board and Director
- -----------------------------------------------------         (principal executive officer)
                 WILLIAM WILSON III

                  /s/ JOHN S. MOODY                         Chief Executive Officer, President and
- -----------------------------------------------------         Director (principal executive officer)
                    JOHN S. MOODY

                /s/ RODNEY C. DIMOCK                        Executive Vice President and Director
- -----------------------------------------------------
                  RODNEY C. DIMOCK

                /s/ KEVIN P. MAHONEY                        Chief Financial Officer (principal financial
- -----------------------------------------------------         and principal accounting officer)
                  KEVIN P. MAHONEY

                                                            Director
- -----------------------------------------------------
                   CECIL D. CONLEE

                   /s/ BLAKE EAGLE                          Director
- -----------------------------------------------------
                     BLAKE EAGLE

             /s/ DR. KARL-LUDWIG HERMANN                    Director
- -----------------------------------------------------
               DR. KARL-LUDWIG HERMANN
</TABLE>

                                      II-11
<PAGE>   310

<TABLE>
<CAPTION>
                      SIGNATURE                             TITLE
                      ---------                             -----
<C>                                                         <S>
                 /s/ HANS C. MAUTNER                        Director
- -----------------------------------------------------
                   HANS C. MAUTNER

                                                            Director
- -----------------------------------------------------
                 DR. LUTZ MELLINGER

               /s/ CRAIG R. STAPLETON                       Director
- -----------------------------------------------------
                 CRAIG R. STAPLETON

              /s/ MICHAEL J. G. TOPHAM                      Director
- -----------------------------------------------------
                MICHAEL J. G. TOPHAM

                /s/ DICK VAN DEN BOS                        Director
- -----------------------------------------------------
                  DICK VAN DEN BOS

                                                            Director
- -----------------------------------------------------
               JAN H.W.R VAN DER VLIST

                /s/ DONALD G. FISHER                        Director
- -----------------------------------------------------
                  DONALD G. FISHER

                 /s/ RANDALL A. HACK                        Director
- -----------------------------------------------------
                   RANDALL A. HACK
</TABLE>

                                      II-12
<PAGE>   311

                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
EXHIBIT NO                        EXHIBIT DESCRIPTION
- ----------                        -------------------
<C>           <S>
    2.1       Agreement and Plan of Merger, dated as of February 11, 2000,
              among Equity Office, EOP Partnership, Cornerstone and
              Cornerstone Partnership (included in this Registration
              Statement as Annex A to the Consent Solicitation/Information
              Statement/Prospectus)
    5.1 *     Opinion of Hogan & Hartson L.L.P. regarding the legality of
              the securities being registered on behalf of EOP and EOP
              Partnership
    5.2 *     Opinion of Lionel, Sawyer & Collins regarding the legality
              of the securities being registered on behalf of Cornerstone
    8.1 *     Opinion of Hogan & Hartson L.L.P. regarding the
              qualification of the REIT merger as a reorganization for
              federal income tax purposes and related federal income tax
              consequences
    8.2 *     Opinion of King & Spalding regarding the qualification of
              the REIT merger as a reorganization for federal income tax
              purposes and related federal income tax consequences
    8.3 *     Opinion of Hogan & Hartson L.L.P. regarding the
              qualification by Equity Office Properties Trust as a real
              estate investment trust and EOP Operating Limited
              Partnership as a partnership for federal income tax purposes
    8.4 *     Opinion of King & Spalding regarding the qualification of
              Cornerstone Properties Inc. as a real estate investment
              trust and Cornerstone Properties Limited Partnership as a
              partnership for federal income tax purposes
   23.1       Consent of Ernst & Young LLP (EOP and EOP Partnership)
   23.2       Consent of PricewaterhouseCoopers LLP (Cornerstone and
              Cornerstone Partnership)
   23.3 *     Consent of Hogan & Hartson L.L.P. (included in Exhibit 5.1)
   23.4 *     Consent of Lionel, Sawyer & Collins (included in Exhibit
              5.2)
   23.5 *     Consent of Hogan & Hartson L.L.P. (included in Exhibits 8.1
              and 8.3)
   23.6 *     Consent of King & Spalding (included in Exhibits 8.2 and
              8.4)
   23.7       Consent of J.P. Morgan Securities Inc.
   23.8       Consent of Lazard Freres & Co. LLC
   23.9       Consent of William Wilson III to be named as a trustee
   23.10      Consent of John S. Moody to be named as a trustee
   23.11      Consent of Jan H.W.R van der Vlist to be named as a trustee
   24.1       Equity Office Properties Trust power of attorney (included
              on Equity Office Properties Trust signature page)
   24.2       EOP Operating Limited Partnership power of attorney
              (included on EOP Operating Limited Partnership signature
              page)
   24.3       Cornerstone Properties Inc. power of attorney (included on
              Cornerstone Properties Inc. signature page)
   99.1       Stock Option Agreement, dated February 11, 2000, by and
              among Cornerstone, Equity Office, Deutsche Bank AG and
              Deutscher Herold Lebensversicherungs-AG (incorporated by
              reference to Exhibit 10.1 of Equity Office's Form 8-K dated
              February 16, 2000)
</TABLE>
<PAGE>   312

<TABLE>
<CAPTION>
EXHIBIT NO                        EXHIBIT DESCRIPTION
- ----------                        -------------------
<C>           <S>
   99.2       Voting Agreement, dated February 11, 2000, by and among
              Equity Office, EOP Operating Limited Partnership, WCP
              Services, Inc. and Stichting Pensioenfonds voor de
              Gezondheid, Geotelijke en Maatschappelijke Belagen
              (incorporated by reference to Exhibit 10.2 of Equity
              Office's Form 8-K dated February 16, 2000)
   99.3 *     Cornerstone Partnership -- Form of Consent
   99.4 *     Form of Redemption/Notice of Election
</TABLE>

- ---------------
     * To be filed by amendment.

     (b) Financial Statement Schedules

     The following financial statement schedule was filed with the EOP
Partnership Annual Report on Form 10-K for the year ended December 31, 1999
(File no. 1-13625), filed with the SEC on March 30, 2000, and is incorporated
herein by reference:

        Schedule III -- Real Estate and Accumulated Depreciation

     Schedules not listed above have been omitted because they are inapplicable
or the information required to be set forth therein is contained, or
incorporated by reference, in the consolidated final statements of Equity Office
or notes thereto.
<PAGE>   313

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                                  SCHEDULE III
                               DECEMBER 31, 1999
<TABLE>
<CAPTION>
       COLUMN A            COLUMN B             COLUMN C               COLUMN D                     COLUMN E
- -----------------------  ------------    -----------------------   ----------------   ------------------------------------
                                                                   COST CAPITALIZED
                                                                    SUBSEQUENT TO        GROSS AMOUNT AT WHICH CARRIED
                                         INITIAL COST TO COMPANY     ACQUISITION               AT CLOSE OF PERIOD
                                         -----------------------   ----------------   ------------------------------------
                                                     BUILDING &         LAND &                    BUILDING &
DESCRIPTION              ENCUMBRANCES      LAND     IMPROVEMENTS     IMPROVEMENTS       LAND     IMPROVEMENTS     TOTAL
- -----------              ------------    --------   ------------   ----------------   --------   ------------   ----------
                                                           (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>             <C>        <C>            <C>                <C>        <C>            <C>
Boston, Massachusetts
 Sixty State Street....      $85,420     $     --    $  221,568        $  6,813       $     --    $  228,381    $  228,381
 500 Boylston Street...                    45,132       181,574            (112)        45,132       181,462       226,594
 222 Berkeley Street...                    29,262       118,180             284         29,262       118,464       147,726
 125 Summer Street.....       78,844       15,750        89,250           7,867         15,750        97,117       112,867
 One Memorial Drive....       63,119       22,500        90,873              (6)        22,500        90,867       113,367
San Mateo County,
 California
 Bayhill (4 buildings).       57,764       26,353       105,412           2,166         26,353       107,578       133,931
 Peninsula Office Park
   (7 buildings).......       88,128       25,426       101,705           2,885         25,426       104,590       130,016
 Seaport Centre........       58,000       23,530        94,119           5,259         23,530        99,378       122,908
 Bay Park Plaza (2
   buildings)..........                    13,139        52,556             244         13,139        52,800        65,939
 One Bay Plaza.........                     9,125        36,499           1,165          9,125        37,664        46,789
East Bay, California
 Corporate Centre (2
   buildings)..........                     9,808        39,233             637          9,808        39,870        49,678
 ADP Plaza (2
   buildings)..........                    10,278        41,110             502         10,278        41,612        51,890
 PeopleSoft Plaza......                    10,025        40,100             644         10,025        40,744        50,769
 Norris Tech Center (3
   buildings)..........       16,066        7,223        28,893             379          7,223        29,272        36,495
 Golden Bear Center....       20,477        6,426        25,705             250          6,426        25,955        32,381
 2700 Ygnacio Valley
   Road................                     2,375         9,498             192          2,375         9,690        12,065
 Park Plaza............                     2,673        10,693             323          2,673        11,016        13,689
 1600 South Main.......                     2,501        10,003             175          2,501        10,178        12,679
Atlanta, Georgia
 191 Peachtree
   Street..............                    40,110       228,962           4,575         40,110       233,537       273,647
 200 Galleria..........      120,000(B)    11,994        48,443           3,622         12,726        51,332        64,058
Seattle, Washington
 Washington Mutual
   Tower (3 buildings).       79,100       21,167        43,153         150,354         21,173       193,501       214,674
 110 Atrium Place......       21,517        7,810        31,242             357          7,810        31,599        39,409
 Island Corporate
   Center..............       13,170        3,751        15,004             325          3,751        15,329        19,080
Santa Clara, California
 Pruneyard Office (3
   buildings)..........       60,947       11,896        47,583          13,162         11,896        60,745        72,641
 10 Almaden............                    14,306        57,223             314         14,306        57,537        71,843
 Pruneyard Shopping
   Center..............                     8,491        33,966           1,053          8,491        35,019        43,510
 Embarcadero Place (4
   buildings)..........       38,149       11,728        46,913             (63)        11,728        46,850        58,578
 Pruneyard Inn (C).....                     3,057        12,228           3,126          3,057        15,354        18,411

<CAPTION>
       COLUMN A            COLUMN F      COLUMN G      COLUMN H        COLUMN I
- -----------------------  ------------   -----------   -----------   ---------------

                                                                     LIFE ON WHICH
                                                                    DEPRECIATION IN
                                        (UNAUDITED)   (UNAUDITED)    LATEST INCOME
                         ACCUMULATED       YEAR          DATE        STATEMENTS IS
DESCRIPTION              DEPRECIATION   CONSTRUCTED    ACQUIRED       COMPUTED(A)
- -----------              ------------   -----------   -----------   ---------------
                                       (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>            <C>           <C>           <C>
Boston, Massachusetts
 Sixty State Street....   $ (11,312)           1979    12/31/97            40
 500 Boylston Street...      (9,949)           1988    10/27/97            40
 222 Berkeley Street...      (6,515)           1991    10/27/97            40
 125 Summer Street.....     (12,611)           1989     11/1/95            40
 One Memorial Drive....      (3,812)           1985     4/28/98            40
San Mateo County,
 California
 Bayhill (4 buildings).      (2,836)      1982-1987    12/16/98            40
 Peninsula Office Park
   (7 buildings).......      (2,759)      1971-1998    12/16/98            40
 Seaport Centre........      (2,772)           1988    12/16/98            40
 Bay Park Plaza (2
   buildings)..........      (1,403)      1985-1998    12/16/98            40
 One Bay Plaza.........        (997)           1979    12/16/98            40
East Bay, California
 Corporate Centre (2
   buildings)..........      (1,066)      1985-1987    12/16/98            40
 ADP Plaza (2
   buildings)..........      (1,110)      1987-1989    12/16/98            40
 PeopleSoft Plaza......      (1,069)           1984    12/16/98            40
 Norris Tech Center (3
   buildings)..........        (761)      1984-1998    12/16/98            40
 Golden Bear Center....        (702)           1986    12/16/98            40
 2700 Ygnacio Valley
   Road................        (155)           1984    12/16/98            40
 Park Plaza............        (321)           1986    12/16/98            40
 1600 South Main.......        (271)           1983    12/16/98            40
Atlanta, Georgia
 191 Peachtree
   Street..............     (13,469)           1991    10/27/97            40
 200 Galleria..........      (3,146)           1985    10/27/97            40
Seattle, Washington
 Washington Mutual
   Tower (3
   buildings)..........     (82,749)           1988      5/1/88            40
 110 Atrium Place......        (839)           1981    12/16/98            40
 Island Corporate
   Center..............        (404)           1987    12/16/98            40
Santa Clara, California
 Pruneyard Office (3
   buildings)..........      (1,517)      1971-1999    12/16/98            40
 10 Almaden............      (1,510)           1989    12/16/98            40
 Pruneyard Shopping
   Center..............        (922)          1970s    12/16/98            40
 Embarcadero Place (4
   buildings)..........      (1,221)           1984    12/16/98            40
 Pruneyard Inn (C).....        (339)           1989    12/16/98            40
</TABLE>
<PAGE>   314
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                          SCHEDULE III -- (CONTINUED)
                               DECEMBER 31, 1999
<TABLE>
<CAPTION>
       COLUMN A            COLUMN B             COLUMN C               COLUMN D                     COLUMN E
- -----------------------  ------------    -----------------------   ----------------   ------------------------------------
                                                                   COST CAPITALIZED
                                                                    SUBSEQUENT TO        GROSS AMOUNT AT WHICH CARRIED
                                         INITIAL COST TO COMPANY     ACQUISITION               AT CLOSE OF PERIOD
                                         -----------------------   ----------------   ------------------------------------
                                                     BUILDING &         LAND &                    BUILDING &
DESCRIPTION              ENCUMBRANCES      LAND     IMPROVEMENTS     IMPROVEMENTS       LAND     IMPROVEMENTS     TOTAL
- -----------              ------------    --------   ------------   ----------------   --------   ------------   ----------
                                                           (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>             <C>        <C>            <C>                <C>        <C>            <C>
San Francisco,
 California
 120 Montgomery
   Street..............       48,160       16,427        65,709           2,958         16,427        68,667        85,094
 201 California
   Street..............       44,504       11,350        46,040           2,007         11,350        48,047        59,397
 188 Embarcadero.......       15,606        4,718        18,871             399          4,718        19,270        23,988
Minneapolis, Minnesota
 Norwest Center........      110,000       18,000        33,613         152,888         18,000       186,501       204,501
Washington, D.C./
 Alexandria, Virginia
 Market Square (2
   buildings)..........             (B)    50,199       201,084           2,964         50,199       204,048       254,247
 99 Canal Center.......                     4,551        18,380           1,574          4,551        19,954        24,505
 TransPotomac Plaza 5..       65,000(B)     2,124         8,577           1,000          2,124         9,577        11,701
 11 Canal Center.......                     2,326         9,394             500          2,326         9,894        12,220
Suburban Chicago,
 Illinois
 Corporate 500 Centre
   (4 buildings).......       88,424       30,000       120,163           3,456         30,000       123,619       153,619
 One Lincoln Centre....       65,000(B)     2,192        47,758           4,302          2,192        52,060        54,252
Santa Monica/West Los
 Angeles, California
 West Wilshire (2
   buildings)..........       16,926        7,492        29,970             629          7,492        30,599        38,091
 Wilshire Palisades....       29,047       12,650        52,247           1,291         12,650        53,538        66,188
 Janss Court (D).......       18,357        7,274        29,098             147          7,274        29,245        36,519
 Searise Office
   Tower...............       11,607        6,043        24,172             347          6,043        24,519        30,562
 Commerce Park.........                     2,653        10,613             149             --        13,415        13,415
 429 Santa Monica......                     3,899        15,595             317          3,899        15,912        19,811
Orange County,
 California
 Bixby Ranch...........       28,528        9,681        38,723             300          9,681        39,023        48,704
 18301 Von Karman......                     8,052        32,206           2,224          8,052        34,430        42,482
 2677 South Main.......                     5,696        22,786           1,571          5,696        24,357        30,053
San Diego, California
 Centerside II.........       24,254        7,524        30,094             609          7,523        30,703        38,226
 Crossroads............                     3,207        12,828             222          3,207        13,050        16,257
Los Angeles, California
 700 North Brand.......       26,938        8,112        32,450             145          8,112        32,595        40,707
 Warner Park Center....                     1,746         6,986             123          1,746         7,109         8,855
New York City, New York
 527 Madison Avenue....             (B)    21,440        46,643           2,627         21,440        49,270        70,710
 Tower 56..............       25,024        5,528        25,203           9,434          5,528        34,637        40,165
Conejo Valley
 (Ventura), California
 Westlake Spectrum (2
   buildings)..........                     3,510        14,038             177          3,510        14,215        17,725
 Agoura Hills..........       12,003        3,821        15,284             241          3,821        15,525        19,346

<CAPTION>
       COLUMN A            COLUMN F      COLUMN G      COLUMN H        COLUMN I
- -----------------------  ------------   -----------   -----------   ---------------

                                                                     LIFE ON WHICH
                                                                    DEPRECIATION IN
                                        (UNAUDITED)   (UNAUDITED)    LATEST INCOME
                         ACCUMULATED       YEAR          DATE        STATEMENTS IS
DESCRIPTION              DEPRECIATION   CONSTRUCTED    ACQUIRED       COMPUTED(A)
- -----------              ------------   -----------   -----------   ---------------
                                       (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>            <C>           <C>           <C>
San Francisco,
 California
 120 Montgomery
   Street..............      (1,846)           1955    12/16/98            40
 201 California
   Street..............      (1,845)           1969      6/3/98            40
 188 Embarcadero.......        (504)           1980    12/16/98            40
Minneapolis, Minnesota
 Norwest Center........     (84,164)           1988      7/1/88            40
Washington, D.C./
 Alexandria, Virginia
 Market Square (2
   buildings)..........      (6,142)           1990     11/1/98            40
 99 Canal Center.......      (1,089)           1986    10/27/97            40
 TransPotomac Plaza
   5...................        (544)           1983    10/27/97            40
 11 Canal Center.......        (573)           1986    10/27/97            40
Suburban Chicago,
 Illinois
 Corporate 500 Centre
   (4 buildings).......      (5,958)      1986/1990     1/28/98            40
 One Lincoln Centre....      (4,361)           1986     11/8/96            40
Santa Monica/West Los
 Angeles, California
 West Wilshire (2
   buildings)..........        (411)      1960-1976    12/16/98            40
 Wilshire Palisades....      (2,155)           1981      6/3/98            40
 Janss Court (D).......        (772)           1989    12/16/98            40
 Searise Office
   Tower...............        (657)           1975    12/16/98            40
 Commerce Park.........        (349)           1977    12/16/98            40
 429 Santa Monica......        (411)           1982    12/16/98            40
Orange County,
 California
 Bixby Ranch...........      (1,024)           1987    12/16/98            40
 18301 Von Karman......        (971)           1991    12/16/98            40
 2677 South Main.......        (681)           1987    12/16/98            40
San Diego, California
 Centerside II.........        (803)           1987    12/16/98            40
 Crossroads............        (358)           1983    12/16/98            40
Los Angeles, California
 700 North Brand.......        (852)           1981    12/16/98            40
 Warner Park Center....        (183)           1986    12/16/98            40
New York City, New York
 527 Madison Avenue....      (3,762)           1986     2/14/97            40
 Tower 56..............      (3,501)           1983     4/24/96            40
Conejo Valley
 (Ventura), California
 Westlake Spectrum (2
   buildings)..........        (367)           1990    12/16/98            40
 Agoura Hills..........        (417)           1987    12/16/98            40
</TABLE>
<PAGE>   315
                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                          SCHEDULE III -- (CONTINUED)
                               DECEMBER 31, 1999
<TABLE>
<CAPTION>
       COLUMN A            COLUMN B             COLUMN C               COLUMN D                     COLUMN E
- -----------------------  ------------    -----------------------   ----------------   ------------------------------------
                                                                   COST CAPITALIZED
                                                                    SUBSEQUENT TO        GROSS AMOUNT AT WHICH CARRIED
                                         INITIAL COST TO COMPANY     ACQUISITION               AT CLOSE OF PERIOD
                                         -----------------------   ----------------   ------------------------------------
                                                     BUILDING &         LAND &                    BUILDING &
DESCRIPTION              ENCUMBRANCES      LAND     IMPROVEMENTS     IMPROVEMENTS       LAND     IMPROVEMENTS     TOTAL
- -----------              ------------    --------   ------------   ----------------   --------   ------------   ----------
                                                           (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>             <C>        <C>            <C>                <C>        <C>            <C>
Other
 U.S. West (Murray,
   Utah)...............                     3,311        13,245             185          3,311        13,430        16,741
 Exposition Centre
   (Sacramento, CA)....        5,081        1,772         7,089             209          1,772         7,298         9,070
Projects under
 development...........           --       46,720        10,103           6,309         46,132        17,000        63,132
                         -----------     --------    ----------        --------       --------    ----------    ----------
Grand Total............   $1,435,160     $707,854    $2,900,650        $405,796       $705,350    $3,308,948    $4,014,298
                         ===========     ========    ==========        ========       ========    ==========    ==========

<CAPTION>
       COLUMN A            COLUMN F      COLUMN G      COLUMN H        COLUMN I
- -----------------------  ------------   -----------   -----------   ---------------

                                                                     LIFE ON WHICH
                                                                    DEPRECIATION IN
                                        (UNAUDITED)   (UNAUDITED)    LATEST INCOME
                         ACCUMULATED       YEAR          DATE        STATEMENTS IS
DESCRIPTION              DEPRECIATION   CONSTRUCTED    ACQUIRED       COMPUTED(A)
- -----------              ------------   -----------   -----------   ---------------
                                       (DOLLAR AMOUNTS IN THOUSANDS)
<S>                      <C>            <C>           <C>           <C>
Other
 U.S. West (Murray,
   Utah)...............        (375)           1985    12/16/98            40
 Exposition Centre
   (Sacramento, CA)....        (222)           1984    12/16/98            40
Projects under
 development...........          --             N/A          --           N/A
                          ---------     -----------    --------           ---
Grand Total............   $(291,834)
                          =========
</TABLE>

- ---------------
(A) The life to compute depreciation on Buildings is 40 years. The life to
    compute depreciation on Building Improvements is 3 to 40 years.

(B) The three notes arising from the acquisition of several properties from PGGM
    (a major stockholder and related party) are cross-collateralized, having the
    effect of forming a "collateral pool" for the underlying notes. In addition,
    the $181.0 million first mortgage loan on Market Square, which the Company
    purchased from PGGM in 1997, has been pledged as collateral for the $120.0
    million 200 Galleria loan.

(C) The Pruneyard Inn is a 172-room hotel.

(D) In addition to 92,000 square feet of retail and office space, Janss Court
    contains 32 apartments comprising 33,000 rentable square feet of residential
    space.
<PAGE>   316

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                                  SCHEDULE III
                               DECEMBER 31, 1999
                                  (CONTINUED)

RECONCILIATION OF "REAL ESTATE AND ACCUMULATED DEPRECIATION"

<TABLE>
<CAPTION>
                                                                 1999          1998
                                                              ----------    ----------
<S>                                                           <C>           <C>
INVESTMENT IN REAL ESTATE
Balance, beginning of period................................  $4,340,449    $1,918,746
  Additions during period:
     Acquisitions...........................................      38,437     2,410,427
     Improvements...........................................      14,904        30,690
  Deductions during period:
     Properties disposed of.................................    (358,670)      (19,414)
     Retirements and writeoffs..............................     (20,822)           --
                                                              ----------    ----------
Balance, end of period......................................  $4,014,298    $4,340,449
                                                              ==========    ==========
ACCUMULATED DEPRECIATION
Balance, beginning of period................................  $  288,448    $  231,421
  Additions during period:
     Depreciation...........................................      96,726        57,031
  Deductions during period:
     Properties disposed of.................................     (73,131)
     Retirements and writeoffs..............................     (20,209)           (4)
                                                              ----------    ----------
                                                              $  291,834    $  288,448
                                                              ==========    ==========
</TABLE>
                                       2
<PAGE>   317

                   CORNERSTONE PROPERTIES LIMITED PARTNERSHIP

                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                                  SCHEDULE III
                               DECEMBER 31, 1999
                                  (CONTINUED)

RECONCILIATION OF "REAL ESTATE AND ACCUMULATED DEPRECIATION"

<TABLE>
<CAPTION>
                                                                   1999             1998
                                                              --------------    ------------
<S>                                                           <C>               <C>
INVESTMENT IN REAL ESTATE
Balance, beginning of period................................  $    4,340,449    $  1,918,746
Additions resulting from consolidation of real estate
  partnerships:
  Land......................................................              --              --
  Buildings and Improvements................................              --              --
                                                              --------------    ------------
Additions during the period:
  Land......................................................     192,146,936      10,572,247
  Deferred lease costs......................................       9,432,143       5,262,535
  Buildings and improvements................................     946,518,418     108,878,526
Deductions during the period:
  Retirements and writeoffs.................................         486,996       1,309,286
                                                              --------------    ------------
Balance at end of period....................................  $1,149,557,773    $124,203,684
                                                              ==============    ============
ACCUMULATED DEPRECIATION
Balance at beginning of period..............................     198,685,707      20,939,530
Additions resulting from consolidation of real estate
  partnerships:
Additions charged to operating expenses.....................      31,452,922     179,055,463
Deductions due to retirements and writeoffs.................         486,996       1,309,286
                                                              --------------    ------------
Balance at end of period....................................  $  229,651,633    $198,685,707
                                                              ==============    ============
</TABLE>
                                       3

<PAGE>   1
                                                                    Exhibit 23.1


We consent to the reference to our firm under the caption "Experts" in the
Registration Statement (Form S-4) and related Prospectus of Equity Office
Properties Trust and EOP Operating Limited Partnership for the registration of
common shares of beneficial interest and units of limited partnership interest
related to the merger with Cornerstone Properties Limited Partnership and to the
incorporation by reference therein of our reports, both dated February 8, 2000,
except for Note 24, as to which the date is February 15, 2000, on the
consolidated financial statements and schedule of Equity Office Properties Trust
and of EOP Operating Limited Partnership included in their respective Annual
Reports (Form 10-K) for the year ended December 31, 1999, both filed with the
Securities and Exchange Commission.


                                                           /s/ ERNST & YOUNG LLP
                                                               Ernst & Young LLP




Chicago, Illinois
April 24, 2000


<PAGE>   1

                                                                    Exhibit 23.2


                       CONSENT OF INDEPENDENT ACCOUNTANTS


We hereby consent to the incorporation by reference in this Registration
Statement on Form S-4 of Equity Office Properties Trust, EOP Operating Limited
Partnership and Cornerstone Properties Inc. of our report dated March 3, 2000
relating to the consolidated financial statements of Cornerstone Properties
Inc, which appears in Cornerstone Properties Inc.'s Annual Report on Form 10-K
for the year ended December 31, 1999. We also hereby consent to the use in this
Registration Statement on Form S-4 of our report dated April 12, 2000 relating
to the financial statements and the financial statement schedule of Cornerstone
Properties Limited Partnership, which appears in such Registration Statement.
We also consent to the references to us under the headings "Experts" and
"Selected Financial Data" in such Registration Statement.


/s/ PricewaterhouseCoopers LLP
PricewaterhouseCoopers LLP

New York, New York
April 25, 2000



<PAGE>   1
                                                                    Exhibit 23.7

                            [J.P. MORGAN LETTERHEAD]

                     CONSENT OF J.P. MORGAN SECURITIES INC.


       We hereby consent to (i) the use of our opinion letter dated February 11,
2000 to The Board of Trustees of Equity Office Properties Trust included as
Annex B to the Consent Solicitation/Information Statement/Prospectus which forms
a part of the Registration Statement on Form S-4 relating to the proposed merger
of EOP Operating Limited Partnership and Cornerstone Properties Limited
Partnership, and (ii) the references to such opinion in such Consent
Solicitation/Information Statement/Prospectus. In giving such consent, we do not
admit that we come within the category of persons whose consent is required
under Section 7 of the Securities Act of 1933, as amended, or the rules and
regulations of the Securities and Exchange Commission thereunder, nor do we
hereby admit that we are experts with respect to any part of such Registration
Statement within the meaning of the term "experts" as used in the Securities Act
of 1933, as amended, or the rules and regulations of the Securities and Exchange
Commission thereunder.

J.P. MORGAN SECURITIES INC.


By:      /s/ JOHN R. PERKINS
         -------------------------
         Name:  John R. Perkins
         Title:  Vice President

April 18, 2000


<PAGE>   1
                                                                    Exhibit 23.8


                     [LETTERHEAD OF LAZARD FRERES & CO. LLC]


                       CONSENT OF LAZARD FRERES & CO. LLC

            We hereby consent to (i) the use of our opinion letter dated
February 11, 2000 to the Board of Directors of Cornerstone Properties Inc.,
included as Annex C to the Consent Solicitation/Information Statement/Prospectus
which forms a part of the Registration Statement on Form S-4 relating to the
proposed acquisition of Cornerstone Properties Limited Partnership by EOP
Operating Limited Partnership, and (ii) the references to such opinion in such
Consent Solicitation/Information Statement/Prospectus. In giving such consent,
we do not admit that we come within the category or persons whose consent is
required under Section 7 of the Securities Act of 1933, as amended, or the rules
and regulations of the Securities and Exchange Commission thereunder, nor do we
hereby admit that we are "experts" as used in the Securities Act of 1933, as
amended, or the rules and regulations of the Securities and Exchange Commission
thereunder.


Dated:  April 25, 2000

                                                         LAZARD FRERES & CO. LLC


                                                   By: /s/ MATTHEW J. LUSTIG
                                                      --------------------------
                                                        Name: Matthew J. Lustig
                                                        Title: Managing Director




<PAGE>   1
                                                                    Exhibit 23.9

       Consent to be Named as a Trustee of Equity Office Properties Trust

            I hereby consent, pursuant to Rule 438 of the Securities Act of
1933, as amended, to be named as a person to become a trustee of Equity Office
Properties Trust, a Maryland real estate investment trust ("Equity Office"),
under the circumstances described in the registration statement on Form S-4
filed by Equity Office, EOP Operating Limited Partnership, a Delaware limited
partnership ("EOP Partnership"), and Cornerstone Properties Inc., a Nevada
corporation, with the Securities and Exchange Commission in connection with the
merger of Cornerstone Properties Limited Partnership, a Delaware limited
partnership, with and into EOP Partnership.

                                                       /s/ WILLIAM WILSON III
                                                       -------------------------
                                                       William Wilson III
                                                       Date: April 12, 2000


<PAGE>   1
                                                                   Exhibit 23.10

       Consent to be Named as a Trustee of Equity Office Properties Trust

            I hereby consent, pursuant to Rule 438 of the Securities Act of
1933, as amended, to be named as a person to become a trustee of Equity Office
Properties Trust, a Maryland real estate investment trust ("Equity Office"),
under the circumstances described in the registration statement on Form S-4
filed by Equity Office, EOP Operating Limited Partnership, a Delaware limited
partnership ("EOP Partnership"), and Cornerstone Properties Inc., a Nevada
corporation, with the Securities and Exchange Commission in connection with the
merger of Cornerstone Properties Limited Partnership, a Delaware limited
partnership, with and into EOP Partnership.

                                                         /s/ JOHN S. MOODY
                                                         -----------------------
                                                         John S. Moody
                                                         Date: April 11, 2000


<PAGE>   1
                                                                   Exhibit 23.11

       Consent to be Named as a Trustee of Equity Office Properties Trust

       I hereby consent, pursuant to Rule 438 of the Securities Act of 1933, as
amended, to be named as a person to become a trustee of Equity Office Properties
Trust, a Maryland real estate investment trust ("Equity Office"), under the
circumstances described in the registration statement on Form S-4 filed by
Equity Office, EOP Operating Limited Partnership, a Delaware limited partnership
("EOP Partnership"), and Cornerstone Properties Inc., a Nevada corporation, with
the Securities and Exchange Commission in connection with the merger of
Cornerstone Properties Limited Partnership, a Delaware limited partnership, with
and into EOP Partnership.

                                                          /s/ JAN VAN DER VLIST
                                                          ----------------------
                                                          Jan van der Vlist
                                                          Date: April 11, 2000



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