EXHIBIT A JOINT FILING AGREEMENT

EXHIBIT A
JOINT FILING AGREEMENT

SCHEDULE 13G
JOINT FILING AGREEMENT

     This Agreement is dated as of August 30, 2007 by and between Mercury Fund VI, Ltd. (“Mercury VI”), Mercury Fund VII, Ltd. (“Mercury VII”), Mercury Ventures, Ltd. (“Mercury Ventures”), Mercury Ventures II, Ltd. (“Mercury Ventures II”), Mercury Management, L.L.C. (“Mercury Management”) and Xxxxx X. Xxxx (“Xx. Xxxx”).

     WHEREAS, pursuant to paragraph (k)(1) of Rule 13d-1 promulgated under Section 13d(1) of the Securities Exchange Act of 1934, as amended (the “Act”), the parties hereto have decided to satisfy their filing obligations under the Act by a single joint filing.

     NOW, THEREFORE, the undersigned do hereby agree as follows:

     1. The Schedule 13G (the “Schedule 13G”) with respect to Gensym Corp., a Delaware corporation, to which this Agreement is attached as Exhibit A is filed on behalf of Mercury VI, Mercury VII, Mercury Ventures, Mercury Ventures II, Mercury Management and Xx. Xxxx. Mercury VI, Mercury VII, Mercury Ventures and Mercury Management hereby authorize Xx. Xxxx to file the Schedule 13G on their behalf.

     2. Each of Mercury VI, Mercury VII, Mercury Ventures, Mercury Ventures II, Mercury Management and Xx. Xxxx is responsible for the completeness and accuracy of the information concerning such person or entity contained therein; provided that each person or entity is not responsible for the completeness or accuracy of the information concerning any other person or entity making such filing.

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     IN WITNESS WHEREOF, the undersigned hereunto set their hands as of the date first above written.

		MERCURY FUND VI, LTD.
		By:		MERCURY VENTURES, LTD.
				General Partner
				By:		MERCURY MANAGEMENT, L.L.C.
						General Partner
						By:		/s/ Xxxxx X. Xxxx
						Name:		Xxxxx X. Xxxx
						Title:		Manager
		MERCURY FUND VII, LTD.
		By:		MERCURY VENTURES, LTD.
				General Partner
				By:		MERCURY MANAGEMENT, L.L.C.
						General Partner
						By:		/s/ Xxxxx X. Xxxx
						Name:		Xxxxx X. Xxxx
						Title:		Manager
		MERCURY VENTURES, LTD.
		By:		MERCURY MANAGEMENT, L.L.C.
				General Partner
				By:		/s/ Xxxxx X. Xxxx
				Name:		Xxxxx X. Xxxx
				Title:		Manager
		MERCURY VENTURES II, LTD.
		By:		MERCURY MANAGEMENT, L.L.C.
				General Partner
				By:		/s/ Xxxxx X. Xxxx
				Name:		Xxxxx X. Xxxx
				Title:		Manager

		MERCURY MANAGEMENT, L.L.C.
		By:		/s/ Xxxxx X. Xxxx
		Name:		Xxxxx X. Xxxx
		Title:		Manager
		/s/ Xxxxx X. Xxxx
		Name: Xxxxx X. Xxxx