Document:

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                                                                   Exhibit 10(m)

           ASSIGNMENT AND ASSUMPTION OF AGREEMENT OF SALE AND PURCHASE

                           THIS ASSIGNMENT AND ASSUMPTION OF AGREEMENT OF SALE
         AND PURCHASE made as of this 9th day of September, 1999 between YORK
         AVENUE DEVELOPMENT, INC., a New York Corporation, with an office at
         1334 York Avenue, New York, New York 10021 (the "Assignor") and
         SOTHEBY'S, INC., a New York corporation, with offices at 1334 York
         Avenue, New York, New York 10021 (the "Assignee").

                              W I T N E S S E T H:

                  WHEREAS, Assignor, as purchaser, entered into an Agreement of
Sale and Purchase dated as of September 9, 1999 with The Benenson Capital
Company, Lawrence A. Benenson and Raymond E. Benenson, as sellers, relating to
the purchase of the property at 1334 York Avenue, New York, New York (the
"Agreement");

                  NOW, THEREFORE, in consideration of the sum of One ($1.00)
Dollar and other good and valuable consideration paid by Assignee to Assignor,
the receipt and sufficiency whereof is hereby acknowledged by Assignor does
hereby sell, assign and transfer unto Assignee all of Assignor's right, title
and interest in and to the Agreement, including without limitation, all of the
Assignor's right, title and interest in and to any down payment deposited with
Seller's attorney in escrow in accordance with the Agreement.

                  Assignee hereby accepts the assignment and assumes all the
terms, covenants and conditions of the Agreement on Assignor's part to be
performed.

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                  TO HAVE AND TO HOLD unto Assignee, its successors and assigns
forever, subject to the terms of the Agreement.

                  IN WITNESS WHEREOF, the undersigned have executed this
Assignment and Assumption of Agreement of Sale and Purchase as of the date set
forth above.

                                            ASSIGNOR:
                                            YORK AVENUE DEVELOPMENT, INC.

                                            By: /s/ William F. Ruprecht
                                               ---------------------------
                                                Name: William F. Ruprecht
                                                Title:

                                            ASSIGNEE:
                                            SOTHEBY'S, INC.

                                            By: /s/ William F. Ruprecht
                                               ---------------------------
                                                Name: William F. Ruprecht
                                                Title:<PAGE>

                                                                   Exhibit 10(n)

                                    GUARANTY

                  KNOW ALL MEN BY THESE PRESENTS THAT

                  WHEREAS:

                  1. The Benenson Capital Company, a New York general
partnership, Lawrence A. Benenson and Raymond E. Benenson, (referred to
collectively herein as "SELLER") having an office at 708 Third Avenue, New York,
New York 10017, concurrently with the delivery of this instrument has entered
into an Agreement of Sale and Purchase of even date herewith, with York Avenue
Development, Inc. (referred to herein as "PURCHASER"), a New York corporation,
having an office at 1334 York Avenue, New York, New York 10021, affecting
premises known as and by the street number 1334 York Avenue in the Borough of
Manhattan, City, County and State of New York, which aforesaid agreement is
hereby incorporated in this instrument by reference (the aforesaid agreement is
referred to herein as the "AGREEMENT" and the premises demised therein is
referred to herein as the "PREMISES"); and

                  2. The undersigned, Sotheby's Holdings, Inc., a Michigan
corporation (referred to herein as "GUARANTOR"), having an office at 1334 York
Avenue, New York, New York 10021, is the indirect owner of all of the issued and
outstanding stock of Purchaser; and

                  3. Guarantor acknowledges that Seller would not enter into the
Agreement unless this Guaranty accompanied the execution and delivery of the
Agreement.

                  NOW, THEREFORE, in consideration of the execution and delivery
of the Agreement by Seller and Purchaser, and of other good and valuable
consideration, the receipt and sufficiency whereof is hereby acknowledged by
Guarantor;

                  FIRST:   The undersigned Guarantor does hereby:

    11            Covenant and agree with Seller that if Purchaser, its
         successors or assigns, shall default at any time in the payment of the
         Purchase Price or any part thereof or any other payments provided to be
         paid by Purchaser in the Agreement (collectively, the "Amounts"), or in
         the observance or performance of

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         any of the terms, covenants or conditions of the Agreement on
         Purchaser's part to be observed or performed, and such defaults shall
         not be cured before the expiration of any applicable grace period, then
         Guarantor will, on not less than ten (10) days prior written notice,
         well and truly observe and perform said terms, covenants and conditions
         and pay to Seller the Amounts and any other charges payable by
         Purchaser under the Agreement, or any arrears thereof that may remain
         due to Seller, and all damages, including, but not limited to, any
         damages payable pursuant to the Agreement that may arise in consequence
         of Purchaser's insolvency or such default in the observance or
         performance of any of said terms, covenants or conditions; and

    12            Covenant and agree with Seller that Guarantor may, at
         Seller's option, be joined in any action or proceeding commenced by
         Seller against Purchaser in connection with or based upon the Agreement
         or any term, covenant or condition thereof, and that recovery may be
         had against Guarantor in such action or proceeding or in any
         independent action or proceeding against Guarantor without Seller, or
         its assigns, first asserting, prosecuting or exhausting any remedy or
         claim against Purchaser, its successors or assigns; and

    13            Covenant and agree with Seller that this Guaranty shall
         remain and continue in full force and effect notwithstanding any
         modifications or amendments of the Agreement; and

    14            Covenant to indemnify and save Seller harmless of and from
         all cost, liability, damage and expense including, but not limited to,
         reasonable counsel fees, which may arise by reason of Purchaser's
         default under the Agreement and not cured before the expiration of any
         applicable grace period, or Purchaser's insolvency, or Guarantor's
         default hereunder; and

    15            Covenant and agree with Seller that this Guaranty shall not
         be terminated, affected or impaired by reason of any action which
         Seller may take or fail to take against Purchaser or by reason of any
         waiver of, or failure to enforce, any of the rights or remedies
         reserved to Seller in the Agreement, or otherwise, provided, however,
         that Guarantor shall be entitled to the same defenses that may legally
         be asserted by Purchaser; and

    16            Waive notice of the acceptance of this Guaranty and of any
         and all defaults by Purchaser in the payment of the Amounts, and of any
         and all defaults by Purchaser in the observance or performance of any
         of the terms, covenants or conditions of the Agreement on Purchaser's
         part to be observed or performed, and of any and all notices or demands
         which may be given by Seller to Purchaser, whether or not required to
         be given to Purchaser under the terms of the Agreement; and

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    17            Acknowledge that this Guaranty is a guarantee of payment
         and not of collection in respect to any obligations which may accrue to
         Seller from Purchaser under the provisions of the Agreement; and

    18            Covenant to and agree with Seller that the validity
         hereunder shall in no way be terminated, affected or otherwise impaired
         by reason of any assignment or transfer of Purchaser's interest in the
         Agreement; and

    19            Covenant to and agree with Seller that no failure to
         exercise and no delay in exercising, on the part of Seller, of any
         right, power or privilege under this Guaranty or at law shall operate
         as a waiver thereof, nor shall any single or partial exercise of any
         right, power or privilege preclude any other or further exercise
         thereof, or the exercise of any other power or right. The rights and
         remedies provided in this Guaranty are cumulative and not exclusive of
         any rights or remedies provided by law.

                  SECOND: The provisions of this Guaranty shall be binding upon
said Guarantor, its successors and assigns and shall inure to the benefit of
Seller, its successors and assigns, and shall not be deemed waived or modified
unless specifically set forth in writing, executed by Seller and delivered to
Guarantor.

                  THIRD: Guarantor agrees that any bills, statements, notices,
demands, requests or other communications given or required to be given to
Guarantor under this Guaranty at Seller's election, shall be addressed to
Guarantor at the above address, by certified mail, return receipt optional.

                  FOURTH: The officer executing this Guaranty on behalf of the
undersigned Guarantor represents to Seller that said officer has been duly
authorized by the undersigned Guarantor to execute and deliver this Guaranty on
behalf of the undersigned Guarantor and that execution and delivery of this
Guaranty is a proper and authorized act of the undersigned Guarantor and does
not violate the Articles of Incorporation or the By-Laws of the undersigned
Guarantor or the Laws of the State of New York.

                  IN WITNESS WHEREOF, the undersigned Guarantor has signed and
sealed this Guaranty this 9th day of September, 1999.

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                                           Sotheby's Holdings, Inc.

                                           By: /s/ William S. Sheridan
                                              -------------------------
                                               William S. Sheridan

                                       4
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                          CERTIFICATE OF ACKNOWLEDGMENT

STATE OF NEW YORK   )
                    : ss.:
COUNTY OF NEW YORK  )

                  On the _____ day of _______________, in the year ___ before
me, the undersigned, a Notary Public in and said State, personally appeared
____________________________________, personally known to me or proved to me on
the basis of satisfactory evidence to be the individual(s) whose name(s) is
(are) subscribed to the within instrument and acknowledged to me that
he/she/they executed the same in his/her/their capacity (ies), and that by
his/her/their signature (s) on the instrument, the individual(s), or the person
upon behalf of which the individual(s) acted, executed the instrument.

                                                        Notary Public

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