Exhibit (d)(4)

               [GRAY CARY TECHNOLOGY'S LEGAL EDGE(R) LETTERHEAD]


December 18, 2001
VIA FACSIMILE                                            OUR FILE NO. 1090303-1

Mr. Christopher L. Kaufman
Latham & Watkins
135 Commonwealth Drive
Menlo Park, CA 94025

RE:  MENTOR GRAPHICS CORPORATION OFFER TO PURCHASE ALL OUTSTANDING SHARES OF
     IKOS SYSTEMS, INC. COMMON STOCK

Dear Kit:

I have received your letter dated December 18, 2001 and have reviewed your
proposal that IKOS waive certain provisions of the form of confidentiality
agreement provided by our letter dated December 12, 2001 in favor of Mentor
Graphics Corporation, Synopsys, Inc. and any other third parties accepting the
terms of the confidentiality agreement. I have also discussed your proposal
with the IKOS Board of Directors.

The proposed waiver would, in our view, potentially result in a breach of
Section 5.2 of the Agreement and Plan of Merger and Reorganization by and among
IKOS, Synopsys, Inc. and Oak Merger Corporation. In addition, IKOS does not
believe that the proposed waiver would be in the best interest of IKOS and its
stockholders, as the provisions for a standstill and a nonsolicitation clause
are for the benefit of IKOS. IKOS will continue to comply with its obligations
under the Merger Agreement.

We look forward to receipt of an executed copy of the nondisclosure agreement
in the form provided by my letter dated December 12, 2001.

Very truly yours,

GRAY CARY WARE & FREIDENRICH LLP


By: /s/ Diane Holt Frankle
   _____________________________

Diane Holt Frankle
dfrankle@graycary.com


cc:  Ramon A. Nunez
     Joseph W. Rockom