Document:

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                                                                    EXHIBIT 10.2

                                    FORM OF

                                  DEMAND NOTE

                                                          Nashua, New Hampshire

$[        ]                                            [_________________, 2001]

11 Riverside Street, Nashua, NH 03062

     For value received, [        ] (the "Borrower"), having an address of c/o
                                          --------
Storage Computer Corporation, 11 Riverside Street, Nashua, NH 03062, hereby
unconditionally promises to pay to the order of Storage Computer Corporation or
registered assigns (the "Lender"), having a usual place of business at 11
                         ------
Riverside Street, Nashua, New Hampshire 03062, ON DEMAND, the principal sum of
[      ] and [__]/100 Dollars ($[    ]), or such lesser sum as shall have been
advanced to the Borrower by the Lender, together with interest thereon, all as
hereafter provided.  Such principal sum, together with all interest incurred
thereon and all other fees and costs, shall be due and payable ON DEMAND.  The
Lender's right to make demand is unconditional and unlimited.

     The Lender may make demand, at any time, in the exercise of the Lender's
sole discretion.  The Borrower agrees that, in exercising its discretion, the
Lender may make demand for any reasons which it deems appropriate, and such
reasons may be related or unrelated to the Borrower, its business or financial
condition or prospects.  The Lender's right to make demand is a continuing
right, and acceptance by the Lender of any payment after demand shall not be
deemed a waiver of such right to make demand on any other occasion.

     Prior to the date upon which the balance of this Note becomes due and
payable as described herein, the unpaid principal balance outstanding, from time
to time, hereunder shall accrue interest at a fixed rate equal to the Applicable
Federal Rate in effect on the date hereof. "Applicable Federal Rate" means the
Federal short-term rate as that term is defined in Section 1274(d) of the
Internal Revenue Code of 1986, as amended. Interest shall be computed on the
basis of a 360-day year and a 30-day month and shall be compounded semi-
annually. Notwithstanding any other provision of this Note, the Lender does not
intend to charge and the Borrower shall not be required to pay any interest or
other fees or charges in excess of the maximum amount permitted by applicable
law; any payments in excess of such maximum shall be refunded to the Borrower or
credited to reduce principal hereunder. All payments received by the Lender
hereunder will be applied first to costs of collection and fees, if any, then to
interest and the balance to principal.

     All outstanding principal plus accrued and unpaid interest on this Note
shall be immediately due and payable upon notice in writing from Lender to the
Borrower demanding payment in full of the loan evidenced hereby; provided,
however, that the Borrower shall not be in default under the terms of this Note
unless and until the Borrower fails to pay the balance due on this Note within
five (5) days after demand is made. All accrued and unpaid interest on this Note
shall be paid upon payment of the principal of the Note, whether by demand or
otherwise. At the time that the payment of the balance of this Note becomes due
and following the expiration of any grace period provided for herein, the Lender
may proceed with every remedy available at law or in equity.
<PAGE>

     Principal and interest shall be payable in lawful money of the United
States of America, at the address of the Lender set forth above or at such other
address as the Lender or any permitted subsequent holder may designate from time
to time to the Borrower in writing.  If any day on which a payment is due
pursuant to the terms of this Note is not a business day, such payment shall be
due on the next business day following.

     In the event any one or more of the provisions of this Note shall for any
reason be held to be invalid, illegal or unenforceable, in whole or in part or
in any respect, or in the event that any one or more of the provisions of this
Note operate or would prospectively operate to invalidate this Note, then and in
any such event, such provision(s) only shall be deemed null and void and shall
not affect any other provision of this Note and the remaining provisions of this
Note shall remain operative and in full force and effect and in no way shall be
affected, prejudiced, or disturbed thereby.

     In case any payment herein provided for shall not be paid when due, the
Lender promises to pay all costs of collection or enforcement of this Note,
including, without limitation, court costs and all reasonable attorney's fees
and expenses incurred or paid by the Lender in enforcing the obligations of the
Borrower.

     This Note may be prepaid, in whole or in part, at any time without penalty
or premium.

     This Note shall be governed by, and construed in accordance with, the laws
of the State of New Hampshire and shall have the effect of a sealed instrument.

     The Borrower and all endorsers and guarantors of this Note herein waive
presentment, notice of nonpayment, protest and all other demand and notices in
connection with the delivery, acceptance, performance or enforcement of this
Note.

                                  By:_________________________________________
Witness:______________________    [                    ]

                                       2<PAGE>

                                                                    Exhibit 10.1

                          PURCHASE AND SALE AGREEMENT

          THIS PURCHASE AND SALE AGREEMENT (this "Agreement"), dated as of
                                                  ---------
November  15, 2001, is by and between CarrAmerica Realty Corporation, a Maryland
real estate investment trust ("Carr"), Security Capital Group Incorporated, a
                               ----
Maryland corporation ("Security Capital") and Security Capital Office Business
                       ----------------
Trust, a Maryland real estate investment trust and indirect subsidiary of
Security Capital ("Sub").
                   ---

          WHEREAS, Security Capital is the beneficial owner of 28,603,417 shares
of Carr common stock, $.01 par value per share, of which Security Capital
desires to sell and Carr desires to purchase 9,200,000 of such shares (the "Carr
                                                                            ----
Shares") subject to the terms described herein;
------

          NOW, THEREFORE, in consideration of the premises and of the mutual
covenants, agreements and warranties herein contained, and for other good and
valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, and intending to be legally bound, the parties hereto agree as
follows:

1.  (a)  Purchase and Sale.  Subject to the terms and upon the conditions herein
         -----------------
    set forth, Carr agrees to purchase and Security Capital agrees to sell on
    the Closing Date (as hereinafter defined) the Carr Shares, free and clear of
    all liens, encumbrances, claims and security interests, in exchange for the
    delivery by Carr to Security Capital of $265,420,000 in immediately
    available funds, payable by wire transfer.

    (b)  Security Capital Purchase Restriction.  Notwithstanding anything to the
         -------------------------------------
    contrary in the stockholders agreement, dated as of April 30, 1996 by and
    among Carr Realty Corporation (now Carr), Carr Realty, L.P., and Security
    Capital Holdings S.A. ("Holdings") and Security Capital U.S. Realty ("SC-
                            --------                                      ---
    Realty"), (the "Stockholders Agreement") and to which Security Capital Group
    ------          ----------------------
    has become party as a result of the transactions between Security Capital
    Group, SC-Realty and Holdings and the consent granted by Carr pursuant to
    that certain letter agreement dated July 28, 2000 between Carr and Security
    Capital Group, on and after the date hereof Security Capital will not, will
    cause each of its controlled Affiliates not to, and will use its reasonable
    best efforts to cause each of its other Affiliates not to, directly or
    indirectly, purchase or otherwise acquire shares of Carr common stock as a
    result of which, after giving effect to such purchase or acquisition,
    Security Capital and its Affiliates will beneficially own more than 37.44%
    of the outstanding shares of Carr common stock. For purposes of this
    Agreement, "Affiliates" shall have the meaning ascribed thereto in
                ----------
<PAGE>

    Rule 12b-2 promulgated under the Securities Exchange Act of 1934, as
    amended, and as in effect on the date hereof.

2.  Representations and Warranties of Carr.  Carr hereby represents and warrants
    --------------------------------------
    to Security Capital as follows:

    (a)  Due Organization.  Carr is duly organized, validly existing and in good
         ----------------
         standing under the laws of the State of Maryland.

    (b)  Authorization.  Carr has the requisite corporate power to enter into
         -------------
         this Agreement and the transactions and agreements contemplated hereby
         and to carry out its obligations hereunder. This Agreement has been
         duly authorized, executed and delivered by Carr and constitutes a valid
         and binding agreement enforceable against Carr in accordance with its
         terms. Neither the execution and delivery of this Agreement, the
         consummation of the transactions and agreements contemplated hereby,
         nor compliance with the terms, conditions or provisions of this
         Agreement will be a violation of any of the terms, conditions or
         provisions of Carr's Articles of Amendment and Restatement, as amended,
         or bylaws or of any material agreement or instrument to which it or one
         of its subsidiaries is a party or by which it or one of its
         subsidiaries or its or their material properties may be bound, or
         constitute a default or create a right of termination or acceleration
         thereunder, except for any such violation, default or right of
         termination or acceleration which has been waived or consented to in
         connection with the transactions contemplated hereby. A special
         committee of the Board of Directors of Carr has authorized and approved
         the transactions contemplated by this Agreement.

    (c)  Carr Shares Outstanding.  As of the date hereof, Carr has outstanding
         -----------------------
         61,030,442 shares of common stock, $01 par value per share.

    (d)  REIT Status.  Carr further represents and warrants that (i) it intends
         -----------
         in its federal income tax return for the tax year that will end on
         December 31, 2001 to be taxed as a real estate investment trust (a
         "REIT") within the meaning of Section 856 of the Internal Revenue Code
          ----
         of 1986, as amended (the "Code"), (ii) it has operated, and intends to
                                   ----
         continue to operate, in such a manner as to qualify as a REIT for 2001,
         and (iii) the consummation of the transactions contemplated by this
         Agreement will not prevent or prohibit Carr from continuing to qualify
         as a REIT for federal income tax purposes, or result in the loss of
         Carr's status as a REIT for federal income tax purposes.

3.  Representations and Warranties of Security Capital.  Security Capital and
    --------------------------------------------------
    Sub hereby represent and warrant to Carr as follows:

                                      -2-
<PAGE>

    (a)  Due Organization.  Security Capital and Sub are each duly organized,
         ----------------
         validly existing and in good standing under the laws of the State of
         Maryland.

    (b)  Authorization.  Security Capital and Sub each have the requisite power
         -------------
         to enter into this Agreement and the transactions and agreements
         contemplated hereby and to carry out its obligations hereunder and
         thereunder. This Agreement has been duly authorized, executed and
         delivered by each of Security Capital and by Sub and constitutes a
         valid and binding agreement of Security Capital and Sub enforceable
         against Security Capital and Sub in accordance with its terms. Neither
         the execution and delivery of this Agreement, consummation of the
         transactions and agreements contemplated hereby, nor compliance with
         the terms, conditions or provisions of this Agreement, will be a
         violation of any of the terms, conditions or provisions of either
         Security Capital's or Sub's charter or bylaws; or of any material
         agreement or instrument to which Security Capital or Sub is a party or
         by which Security Capital or Sub or any of their respective material
         properties may be bound, or constitute a default or create a right of
         termination or acceleration thereunder.

    (c)  Title.  Sub owns the Carr Shares free and clear of all liens,
         -----
         encumbrances, claims and security interests.

    (d)  Ownership.  Sub is the sole legal owner and owner of record and
         ---------
         Security Capital and its subsidiaries (including Sub) are the sole
         beneficial owners of the Carr Shares. For purposes of applying Section
         302(b)(2) of the Code, neither Security Capital or Sub owns in excess
         of 28,603,417 shares of Carr common stock, par value $.01 per share
         (determined taking into account the ownership attribution rules of
         Section 318(a) of the Code including for this purpose any common stock
         that would be issued upon conversion of any shares of Carr's Series A
         Convertible Preferred Stock that are owned by Security Capital, Sub or
         any Affiliate thereof, either actually or by attribution pursuant to
         the ownership attribution rules of Section 318(a) of the Code).

    (e)  Purchases.  None of Security Capital, Sub or any of their Affiliates
         ---------
         has a current plan or intention to purchase any equity securities of
         Carr.

4.  Public Announcements.  The parties hereto will consult with each other
    --------------------
    before issuing, and provide each other with the reasonable opportunity to
    review and comment upon, any press release or other written public
    statements with respect to the transactions contemplated by this Agreement,
    and shall not issue any such press release or make any such public statement
    without the reasonable consent of the other party, except as may be required
    by applicable law, rule or regulation by court process or by obligations
    pursuant to any listing agreement with any national securities exchange or
    transaction reporting system so long as

                                      -3-
<PAGE>

    the other party is notified promptly by the disclosing party of such press
    release or public statement. For the avoidance of doubt, the parties
    acknowledge that Security Capital and Sub will be filing, with respect to
    these transactions, an amendment to its report on Schedule 13D, and Carr
    will be filing, with respect to these transactions, a Current Report on
    Form 8-K.

5.  Closing.  Subject to the satisfaction of the conditions set forth in
    -------
    Section 6 and Section 7, the purchase and sale of the Securities (the
    "Closing") shall occur, at 10:00am (New York City time) on Monday,
     -------
    November, 19, 2001 (such date being the "Closing Date"). The Closing shall
                                             ------------
    take place at the offices of Wachtell, Lipton, Rosen & Katz, 51 West 52nd
    Street, New York, NY 10019, at which time the parties shall make the
    deliveries described below. At the Closing, in addition to any other
    documents required to be delivered under this Agreement, the parties hereto
    shall deliver the documents described below:

      (a)  Deliveries by Carr.  At the Closing, Carr shall deliver or cause to
           ------------------
           be delivered the following to Security Capital:

           (1)  $265,420,000 by wire transfer of immediately available funds to
                the account specified by Security Capital;

           (2)  a certificate of Carr's secretary certifying resolutions of the
                special committee of the Board of Directors of Carr approving
                this Agreement and the transactions contemplated hereby
                (together with an incumbency and signature certificate regarding
                the officer(s) signing on behalf of Carr);

           (3)  a certificate, dated the Closing Date, of an executive officer
                of Carr, certifying that, as of such date, the representations
                and warranties of Carr contained herein are accurate, true and
                correct with the same force and effect as though made on and as
                of such date; and

           (4)  an opinion of Hogan & Hartson L.L.P. (the "Tax Opinion"), in
                                                           -----------
                form and substance reasonably satisfactory to Security Capital,
                to the effect that the purchase by Carr of the Carr Shares from
                Security Capital as contemplated by this Agreement will not
                result in the deemed payment by Carr to Security Capital of a
                dividend for federal income tax purposes that would prevent or
                prohibit Carr from satisfying the distribution requirements
                applicable to REITs under Section 857(a)(1)(a) of the Code for
                Carr's taxable year ending December 31, 2001.

      (b)  Deliveries by Security Capital.  At the Closing, Security Capital
           ------------------------------
           shall deliver or cause to be delivered the following to Carr:

                                      -4-
<PAGE>

           (1)  the Carr Shares, to be delivered by DWAC to an account specified
                by Carr;

           (2)  a certificate, dated the Closing Date, of an executive officer
                of Security Capital, certifying that, as of such date, the
                representations and warranties of Security Capital contained
                herein are accurate, true and correct with the same force and
                effect as though made on and as of such date; and

           (3)  a certificate of Sub's secretary certifying resolutions of the
                Boards of Trustees of Sub approving this Agreement and the
                transactions contemplated hereby (together with an incumbency
                and signature certificate regarding the officer(s) signing on
                behalf of Sub and Security Capital).

6.  Conditions to the Obligations of Carr.  The obligations of Carr under this
    -------------------------------------
    Agreement are subject to the fulfillment of each of the following
    conditions:

      (a)  Performance.  Each of Security Capital and Sub shall have performed
           -----------
           and complied in all material respects with all agreements, covenants,
           obligations and conditions required by this Agreement to be performed
           or complied with by it.

      (b)  Injunctions.  No preliminary or permanent injunction or other final
           -----------
           order by any United States federal or state court shall have been
           issued which prevents the consummation of the transactions
           contemplated hereby.

7.  Conditions to the Obligations of Security Capital.  The obligations of
    -------------------------------------------------
    Security Capital under this Agreement are subject to the fulfillment of each
    of the following conditions:

      (a)  Performance.  Carr shall have performed and complied in all material
           -----------
           respects with all agreements, covenants, obligations and conditions
           required by this Agreement to be performed or complied with by it.

      (b)  Injunctions.  No preliminary or permanent injunction or other final
           -----------
           order by any United States federal or state court shall have been
           issued which prevents the consummation of the transactions
           contemplated hereby.

      (c)  Tax Opinion.  Receipt by Security Capital of the Tax Opinion
           -----------
           described in Section 5(a)(4).

                                      -5-
<PAGE>

8.  Dividends.  Carr represents and warrants that, at a duly held meeting of the
    ---------
    Board of Directors of Carr on November 1, 2001, it passed certain
    resolutions regarding the payment of a regular quarterly dividend (the
    "Dividend") to shareholders of record on November 16,2001 and that a copy of
    such resolutions has been provided to Security Capital. The parties hereto
    agree and acknowledge that for all purposes Sub is and will be the record
    holder of the Carr Shares until the Closing. Carr will not take any action
    between the date hereof and the Closing to cause Sub not to be the record
    holder of the Carr Shares during such period or to in anyway adversely
    affect Sub's right to receive the Dividend.

9.  Survival.  The representations and warranties of the parties shall survive
    --------
    the Closing forever.

10. Indemnification.
    ---------------

      (a)  Each party (the "Indemnifying Party") agrees to indemnify the other
                            ------------------
           party, and each of their affiliates and their respective officers,
           directors, employees, agents and representatives (each, an
           "Indemnified Party" and together the "Indemnified Parties") against,
            -----------------                    -------------------
           and agrees to hold each of them harmless from, any and all
           liabilities, losses, costs, claims, damages, penalties and expenses
           (including, without limitation, reasonable attorneys' fees and
           expenses and costs of investigation and litigation) ("Losses")
                                                                 ------
           (i) incurred or suffered by them relating to or arising out of or in
           connection with any breach of or any inaccuracy in any representation
           or warranty made by the Indemnifying Party in this Agreement or any
           document delivered by it at the Closing pursuant to Section 5 hereof
           or (ii) arising out of or in connection with any action, suit,
           inquiry, or proceeding against or involving any Indemnified Party as
           a result of any Indemnifying Party's actions (or lack thereof) in
           connection with the negotiation or execution of this Agreement or any
           of the transactions contemplated hereby, or based upon any allegation
           or claim that the Indemnified Party is in any way responsible or
           liable for any action (or lack thereof) of the Indemnifying Party. No
           person shall be entitled to indemnification hereunder to the extent
           that the act or omission of such person for which indemnification is
           claimed arises out of such person's fraud, bad faith or willful
           misconduct.

      (b)  As soon as is reasonably practicable after becoming aware of a claim
           for indemnification under this Agreement, the Indemnified Party shall
           promptly give notice to the Indemnifying Party of such claim and the
           amount the Indemnified Party will be entitled to receive hereunder
           from the Indemnifying Party; provided that the failure of the
           Indemnified Party to give notice shall not relieve the Indemnifying
           Party of its obligations hereunder except to the extent (if any) that
           the Indemnifying Party shall have been prejudiced thereby. If the
           Indemnifying Party agrees that it has an indemnification obligation
           but objects that it is obligated to pay only a lesser amount, the
           Indemnified Party shall nevertheless be entitled to recover

                                      -6-
<PAGE>

           promptly from the Indemnifying Party the lesser amount, without
           prejudice to the Indemnified Party's claim for the difference.

      (c)  After receiving a claim as set forth above, the Indemnifying Party
           may, at its own expense, (i) participate in the defense of any claim,
           suit, action or proceeding and (ii) except in the case of a claim
           indemnification for which is available pursuant to clause (ii) of
           paragraph (a) above, as to which this clause (ii) shall be
           inapplicable, upon notice to the Indemnified Party and the
           Indemnifying Party's delivering to the Indemnified Party a written
           agreement that the Indemnified Party is entitled to indemnification
           for all Losses arising out of such claim, suit, action or proceeding,
           assume the defense thereof; provided, however, that (x) the
           Indemnifying Party's counsel is reasonably satisfactory to the
           Indemnified Party, and (y) the Indemnifying Party shall thereafter
           consult with the Indemnified Party upon the Indemnified Party's
           reasonable request for such consultation from time to time with
           respect to such claim, suit, action or proceeding. If the
           Indemnifying Party assumes such defense, the Indemnified Party shall
           have the right (but not the duty) to participate in the defense
           thereof and to employ counsel, at its own expense, separate from the
           counsel employed by the Indemnifying Party. If, however, the
           Indemnified Party reasonably determines in its judgment that
           representation by the Indemnifying Party's counsel of both the
           Indemnifying Party and the Indemnified Party would present such
           counsel with a conflict of interest, then such Indemnified Party may
           employ separate counsel to represent or defend it in any such claim,
           action, suit or proceeding and the Indemnifying Party shall pay the
           reasonable fees and disbursements of such separate counsel. Whether
           or not the Indemnifying Party chooses to defend or prosecute any such
           claim, suit, action or proceeding, all of the parties hereto shall
           cooperate in the defense or prosecution thereof.

      (d)  Notwithstanding anything in this Section 10 to the contrary, neither
           the Indemnifying Party nor the Indemnified Party shall, without the
           written consent of the other, settle or compromise any claim or
           permit a default or consent to entry of any judgment unless the
           claimant and such party provide to such other party an unqualified
           release from all liability in respect of such claim. Notwithstanding
           the foregoing, if a settlement offer solely for money damages is made
           by the applicable third party claimant, and the Indemnifying Party
           notifies the Indemnified Party in writing of the Indemnifying Party's
           willingness to accept the settlement offer and pay the amount called
           for by such offer, and the Indemnified Party declines to accept such
           offer, the Indemnified Party may continue to contest such claim, free
           of any participation by the Indemnifying Party, and the amount of any
           ultimate liability with respect to such claim that the Indemnifying
           Party has an obligation to pay hereunder shall be limited to the
           lesser of (i) the amount of the settlement offer that the Indemnified
           Party declined to accept or (ii) the aggregate Losses of the
           Indemnified Party with respect to such claim. If the Indemnifying
           Party makes any payment on any claim, the Indemnifying Party shall be
           subrogated, to the extent of

                                      -7-
<PAGE>

           such payment, to all rights and remedies of the Indemnified Party to
           any insurance benefits or other claims of the Indemnified Party with
           respect to such claim.

      (e)  In the event that the Indemnifying Party does not elect to assume the
           defense of any claim, suit, action or proceeding, then any failure of
           the Indemnified Party to defend or to participate in the defense of
           any such claim, suit, action or proceeding or to cause the same to be
           done, shall not relieve the Indemnifying Party of its obligations
           hereunder.

11. Successors and Assigns.  This Agreement shall be binding upon, and inure to
    ----------------------
    the benefit of, the parties hereto and their respective heirs, personal
    representatives, successors, assigns and affiliates.

12. Notices.  Any notice or other communication provided for herein or given
    -------
    hereunder to a party hereto shall be in writing and shall be given by
    delivery, by telex, telecopier or by mail (registered or certified mail,
    postage prepaid, return receipt requested) to the respective parties as
    follows:

          If to Carr:

          CarrAmerica Realty Corporation
          1850 K Street, N.W.
          Washington, District of Columbia 20006
          Attention:   Linda A. Madrid, Esq.
          Facsimile:   (202) 729-1160

                with a copy to:

          Hogan & Hartson L.L.P.
          Columbia Square
          555 Thirteenth Street, N.W.
          Washington, D.C.  20004-1109
          Attention:  J. Warren Gorrell, Jr., Esq.
          Facsimile:  (202) 637-5910

          If to Security Capital:

          Security Capital Group Incorporated
          125 Lincoln Avenue
          Santa Fe, New Mexico 87501
          Attention:  Jeffrey A. Klopf
          Facsimile:  (505) 988-8920

                                      -8-
<PAGE>

                with a copy to:

          Wachtell, Lipton, Rosen & Katz
          51 West 52nd Street
          New York, New York  10019
          Attention:  Adam O. Emmerich, Esq.
          Facsimile:  (212) 403-2000

or to such other address with respect to a party as such party shall notify the
other in writing.

13. Waiver.  No party may waive any of the terms or conditions of this
    ------
    Agreement, nor may this Agreement be amended or modified, except by a duly
    signed writing referring to the specific provision to be waived, amended or
    modified.

14. Entire Agreement.  This Agreement constitutes the entire agreement with
    ----------------
    respect to the subject matter hereof, and supersedes all other prior
    agreements and understandings, both written and oral, among the parties
    hereto and their affiliates.

15. Expenses.  Regardless of whether the transactions contemplated hereby are
    --------
    consummated, each party hereto shall pay its own expenses incident to
    preparing for, entering into and carrying out this Agreement and the
    consummation of the transactions contemplated hereby.

16. Captions.  The Section and Paragraph captions herein are for convenience of
    --------
    reference only, do not constitute part of this Agreement and shall not be
    deemed to limit or otherwise affect any of the provisions hereof.

17. Counterparts.  This Agreement may be executed in one or more counterparts,
    ------------
    each of which shall be deemed an original but all of which shall constitute
    one and the same instrument.

18. Governing Law.  This Agreement shall be governed by, and construed and
    -------------
    enforced in accordance with, the laws of the State of Maryland.

19. No Presumption Against Drafter.  Each of the parties hereto has jointly
    ------------------------------
    participated in the negotiation and drafting of this Agreement. In the event
    of an ambiguity or a question of intent or interpretation arises, this
    Agreement shall be construed as if drafted jointly by each of the parties
    hereto and no presumptions

                                      -9-
<PAGE>

    or burdens of proof shall arise favoring any party by virtue of the
    authorship of any of the provisions of this Agreement.

20. Joint and Several Liability.  All representations, warranties, obligations
    ---------------------------
    and liabilities of Security Capital or Sub herein or hereunder shall be
    joint and several.

                           *     *     *     *     *

                                      -10-
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed and delivered as of the day and year first executed.

                              CARRAMERICA REALTY CORPORATION

                              By:  /s/ Thomas A. Carr
                                  ----------------------------------
                                  Name:  Thomas A. Carr
                                  Title: CEO

                              SECURITY CAPITAL GROUP INCORPORATED

                              By:  /s/ C. Ronald Blankenship
                                  ----------------------------------
                                  Name:  C. Ronald Blankenship
                                  Title: Vice Chairman

                              SECURITY CAPITAL OFFICE BUSINESS TRUST

                              By:  /s/ Constance B. Moore
                                  ----------------------------------
                                  Name:  Constance B. Moore
                                  Title: President

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