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                                                                   EXHIBIT 10.23

                          AMENDMENT NO. 1 TO AGREEMENT

        This Amendment No. 1 to the Agreement between IKOS Systems, Inc. (the
"Company") and the undersigned employee of the Company ("Employee") dated
June 2, 1994 is made as of this 26th day of June 2001.

        WHEREAS, the Company and Employee are party to that certain Agreement
dated June 2, 1994 (the "Agreement") by which Company has agreed to pay Employee
the severance benefits specified therein under certain circumstances;

        WHEREAS, Synopsys, Inc. has agreed to acquire the Company (the
"Acquisition").

        WHEREAS, as a result of the Acquisition, the Company and Employee wish
to amend the Agreement in order to make certain changes thereto.

        NOW, THEREFORE, in consideration of Synopsys' willingness to complete
the Acquisition and of the premises and mutual covenants and agreements
hereinafter set forth, the parties agree as follows.

        1. AMENDMENT TO SECTION 1. Section 1 of the Agreement is hereby amended
to read in its entirety as follows:

                "1. Severance. If, within two years after the date of closing of
        the Acquisition (the "Closing Date"), Synopsys terminates Employee's
        employment without "Cause" (as defined below) or Employee terminates his
        employment with Synopsys within 60 days of (i) Employee being required
        to move his office to a location more than thirty (30) miles from the
        Company's principal place of business as it exists on the date
        immediately prior to the Closing Date, or (ii) Employee's base salary
        immediately prior to the Closing Date being reduced, Employee shall
        continue to receive the base salary (including the target bonus for
        which Employee would have been eligible had Employee remained employed
        through the year in which Employee terminated, paid ratably over the
        period in which Employee receives severance), vacation pay, and the
        insurance and health benefits he received immediately prior to the Date
        of Termination (as defined below) until the earlier of (x) the end of
        the Non-Compete Period (as defined below), and (y) the date on which
        Employee violates any of the agreements contained in Section 3 below.
        Employee shall not be entitled to receive any other compensation or
        benefits, including, without limitation, additional stock options
        grants, bonus or other pay. Existing unvested stock options will vest
        100% as of the termination date. Notwithstanding the foregoing, if
        Synopsys releases the Employee from the restrictions contained in
        Section 3 below, at any time after the first anniversary of the Closing
        Date, such release shall terminate Synopsys' obligation to continue the
        base salary, bonus, vacation and benefits as stated above."


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        2. ADDITION OF NEW SECTION 3. The Agreement is hereby amended to add a
new Section 3 to read in its entirely as follows:

                3. Noncompetition Agreement.

                        (a) Employee understands and agrees that this amendment
                to the Agreement is entered into in connection with the merger
                of the Company with and into Synopsys. Employee further
                understands and agrees that he was a substantial shareholder of
                the Company and a key and significant member of either the
                management and/or the technical workforce of the Company and
                that he will receive substantial consideration as a result of
                Synopsys' purchase of his stock interest in the Company.
                Employee and the Company both agree that the Company is engaged
                in its business in each of the fifty states of the United States
                and certain other countries throughout the world and that
                following the Acquisition, the Company and Synopsys will
                continue conduct such business in all parts of the United States
                and certain other countries throughout the world.

                        (b) Employee agrees that at all times during the
                Non-Compete Period, as defined below, not, as an employee,
                agent, consultant, advisor, independent contractor, general
                partner, officer, director, stockholder, investor, lender or
                guarantor of any corporation, partnership or other entity
                (including, but not limited to, Cadence Design Systems, Inc.,
                Mentor Graphics Corporation, Tharas Systems, Inc., Aptix
                Corporation or Axis Corporation), or in any other capacity to
                directly or indirectly:

                                (i) participate in the "Business" (as defined
                        below) anywhere in the United States or in any of the
                        countries in which the Company conducts business as of
                        the Closing Date;

                                (ii) permit his name to be used in connection
                        with any effort involving the Business;

                                (iii) call upon any person who is, at the time
                        the person is called upon, an employee of the Company or
                        Synopsys for the purpose or with the intent of
                        soliciting such employee away from or out of the employ
                        of the Company or Synopsys; or

                                (iv) call upon any person who is, at the time
                        the person is called upon, a customer of the Company or
                        Synopsys for the purpose of soliciting or selling
                        products or services that relate to the Business.

                        (c) For purposes of this agreement "Business" means any
                business, activity or arrangement that engages in the design,
                development, manufacturing, marketing or sale of integrated
                circuit emulation or hardware-based simulation acceleration
                products.

                        (d) "Non-Compete Period" means the period commencing on
                the closing date of the Acquisition and continuing until the
                earlier of (1) one year


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                after the date of termination of Employee's employment and (2)
                the second anniversary of the closing date of the Acquisition.

                        (e) Notwithstanding the foregoing, Employee may (i)
                serve as an employee or consultant for either Cadence Design
                Systems, Inc. or Mentor Graphics, Inc. or their successors,
                provided that Employee does not participate in, provide any
                services for or any benefit to activities within those entities
                which meet the definition of "Business"; and (ii ) own, directly
                or indirectly, solely as an investment, up to one percent (1%)
                of any class of "publicly traded securities" of any business
                that is competitive or substantially similar to the Business.
                The term "publicly traded securities" shall mean securities that
                are traded on a national securities exchange or listed on the
                National Association of Securities Dealers Automated Quotation
                System.

                        (f) If any restriction set forth in this non-competition
                section is found by a court to be unreasonable, then Employee
                agrees, and hereby submits, to the reduction and limitation of
                such prohibition to such area and/or period as shall be deemed
                reasonable. Employee acknowledges that the services that he
                provides to the Company are unique and that irreparable harm
                will be suffered by the Company and Synopsys in the event of the
                breach by the Employee of any of his obligations under this
                agreement, and that the Company and Synopsys will be entitled,
                in addition to its other rights, to enforce by an injunction or
                decree of specific performance the obligations set forth in this
                agreement. Any claims asserted by Employee against Synopsys
                shall not constitute a defense in any injunction action brought
                by Synopsys to obtain specific enforcement of this non-
                competition section.

        3. ADDITION OF NEW SECTION 4. The Agreement is hereby amended to add a
new Section 4 to read in its entirety as follows:

                4. Successors and Assigns. This Agreement shall inure to the
                benefit of each party's successors and assigns. The parties
                specifically agree that Synopsys shall be considered a third
                party beneficiary under this Agreement and shall be entitled to
                enforce all of the terms herein.

        4. AMENDMENT TO SECTION NUMBERS. Former Section numbers 3 through 9 are
hereby amended to be Section numbers 5 through 11, respectively.

        5. NO OTHER AMENDMENT. Other than as set forth above, no other
provisions of the Agreement are amended or changed.

        6. EFFECTIVENESS OF AMENDMENT. This Agreement shall be effective upon
the closing date of the Acquisition.

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


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IKOS SYSTEMS, INC.                          EMPLOYEE


By: /s/ Joseph Rockom                             /s/ Daniel Hafeman
   ---------------------------------        -----------------------------------
Title: CFO                                  Daniel Hafeman
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