GUARANTEE OF LEHMAN BROTHERS HOLDINGS INC

                                EXHIBIT 99.13
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                     The Class 1-A3B Contract Guarantee.
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                             EXHIBIT A to Schedule

                  GUARANTEE OF LEHMAN BROTHERS HOLDINGS INC.

         LEHMAN BROTHERS SPECIAL FINANCING INC. ("Party A") and U.S. Bank,
National Association, solely in its capacity as trustee (the `Grantor
Trustee") of the INDYMAC INDX GRANTOR TRUST SERIES 2006-AR14 1-A3B ("Party B")
have entered into a Master Agreement dated as of October 31, 2006 as amended
from time to time (the "Master Agreement"), pursuant to which Party A and
Party B have entered and/or anticipate entering into one or more transactions
(each a "Transaction"), the Confirmation of each of which supplements, forms
part of, and will be read and construed as one with, the Master Agreement
(collectively referred to as the "Agreement"). This Guarantee is a Credit
Support Document as contemplated in the Agreement. For value received, and in
consideration of the financial accommodation accorded to Party A by Party B
under the Agreement, LEHMAN BROTHERS HOLDINGS INC., a corporation organized
and existing under the laws of the State of Delaware ("Guarantor"), hereby
agrees to the following:

         (a) Guarantor hereby unconditionally guarantees to Party B the due
and punctual payment of all amounts payable by Party A in connection with each
Transaction when and as Party A's obligations thereunder shall become due and
payable in accordance with the terms of the Agreement (whether at maturity, by
acceleration or otherwise). Guarantor hereby agrees, upon written demand by
Party B, to pay or cause to be paid any such amounts punctually when and as
the same shall become due and payable.

          (b) Guarantor hereby agrees that its obligations under this Guarantee
constitute a guarantee of payment when due and not of collection.

         (c) Guarantor hereby agrees that its obligations under this Guarantee
shall be unconditional, irrespective of the validity, regularity or
enforceability of the Agreement against Party A (other than as a result of the
unenforceability thereof against Party B), the absence o