UNITED STATES

SECURITIES & EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D/A

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

Gensym Corporation

(Name of Issuer)

Common Stock

(Title of Class of Securities)

37245R107

(CUSIP Number)

Michael S. Emanuel, Esq.

c/o Loeb Partners Corporation

61 Broadway, New York, N.Y. 10006 (212) 483-7047

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

September 21, 2007

(Date of Event which Requires Filing of this Statement

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240,13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. o

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

*The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No.			37245R107

1. Name of Reporting Person			Loeb Partners Corporation

I.R.S. Identification No. of Above Person

2. Check the Appropriate Box if a Member of a Group			(a) x
			(b) o

3. SEC Use Only

4. Source of Funds			WC, O

5. Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e)			o

6. Citizenship or Place of Organization			Delaware
Number of Shares Beneficially Owned by Each Reporting Person With
	7. Sole Voting Power	15,679

	8. Shared Voting Power	18,069

	9. Sole Dispositive Power	15,679

	10. Shared Dispositive Power	18,069

11. Aggregate Amount of Beneficially Owned by Each Reporting Person				33,748

12. Check if the Aggregate Amount in Row (11) Excludes Certain Shares				o

13. Percent of Class Represented by Amount in Row (11)				0.43%

14. Type of Reporting Person				BD, IA, CO

CUSIP No.			37245R107

1. Name of Reporting Person			Loeb Arbitrage Fund

I.R.S. Identification No. of Above Person

2. Check the Appropriate Box if a Member of a Group			(a) x
			(b) o

3. SEC Use Only

4. Source of Funds			WC, O

5. Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e)			o

6. Citizenship or Place of Organization			New York
Number of Shares Beneficially Owned by Each Reporting Person With
	7. Sole Voting Power	310,938

	8. Shared Voting Power	-0-

	9. Sole Dispositive Power	310,938

	10. Shared Dispositive Power	-0-

11. Aggregate Amount of Beneficially Owned by Each Reporting Person				310,938

12. Check if the Aggregate Amount in Row (11) Excludes Certain Shares				o

13. Percent of Class Represented by Amount in Row (11)				3.92%

14. Type of Reporting Person				BD, PN

CUSIP No.			37245R107

1. Name of Reporting Person			Loeb Offshore Fund Ltd.

I.R.S. Identification No. of Above Person

2. Check the Appropriate Box if a Member of a Group			(a) x
			(b) o

3. SEC Use Only

4. Source of Funds			WC, O

5. Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e)			o

6. Citizenship or Place of Organization			Cayman Islands
Number of Shares Beneficially Owned by Each Reporting Person With
	7. Sole Voting Power	75,351

	8. Shared Voting Power	-0-

	9. Sole Dispositive Power	75,351

	10. Shared Dispositive Power	-0-

11. Aggregate Amount of Beneficially Owned by Each Reporting Person				75,351

12. Check if the Aggregate Amount in Row (11) Excludes Certain Shares				o

13. Percent of Class Represented by Amount in Row (11)				0.95%

14. Type of Reporting Person				CO

CUSIP No.			37245R107

1. Name of Reporting Person			Loeb Arbitrage B Fund LP

I.R.S. Identification No. of Above Person

2. Check the Appropriate Box if a Member of a Group			(a) x
			(b) o

3. SEC Use Only

4. Source of Funds			WC, O

5. Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e)			o

6. Citizenship or Place of Organization			Delaware
Number of Shares Beneficially Owned by Each Reporting Person With
	7. Sole Voting Power	99,846

	8. Shared Voting Power	-0-

	9. Sole Dispositive Power	99,846

	10. Shared Dispositive Power	-0-

11. Aggregate Amount of Beneficially Owned by Each Reporting Person				99,846

12. Check if the Aggregate Amount in Row (11) Excludes Certain Shares				o

13. Percent of Class Represented by Amount in Row (11)				1.26%

14. Type of Reporting Person				PN

CUSIP No.			37245R107

1. Name of Reporting Person			Loeb Offshore B Fund Ltd.

I.R.S. Identification No. of Above Person

2. Check the Appropriate Box if a Member of a Group			(a) x
			(b) o

3. SEC Use Only

4. Source of Funds			WC, O

5. Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e)			o

6. Citizenship or Place of Organization			Cayman Islands
Number of Shares Beneficially Owned by Each Reporting Person With
	7. Sole Voting Power	29,328

	8. Shared Voting Power	-0-

	9. Sole Dispositive Power	29,328

	10. Shared Dispositive Power	-0-

11. Aggregate Amount of Beneficially Owned by Each Reporting Person				29,328

12. Check if the Aggregate Amount in Row (11) Excludes Certain Shares				o

13. Percent of Class Represented by Amount in Row (11)				0.37%

14. Type of Reporting Person				CO

Item 1.	Security and Issuer

The title and class of equity security to which this Statement relates is the Common Stock, 0.01 par value per share (the “Common Stock”), of Gensym Corp. The address of the Issuer’s principal executive offices is 52 2^nd Avenue, Burlington, MA 01803.

Item 2.	Identity and Background

Loeb Arbitrage Fund (“LAF”), 61 Broadway, New York, New York, 10006, is a New York limited partnership. It is a registered broker/dealer. Its general partner is Loeb Arbitrage Management, Inc., (“LAM”), a Delaware corporation, with the same address. Loeb Arbitrage B Fund LP (“LAFB”) is a Delaware limited partnership. Its general partner is Loeb Arbitrage B Management, LLC. The President of these general partners is Gideon J. King. The other officers of LAM are Thomas L. Kempner, Chairman of the Board, President, Peter A. Tcherepnine, Vice President, Edward J. Campbell, Vice President. Loeb Partners Corporation (“LPC”), 61 Broadway, New York, New York, 10006, is a Delaware corporation. It is a registered broker/dealer and a registered investment adviser. Thomas L. Kempner is its President and a director and its Chief Executive Officer. Norman N. Mintz is a Vice President and also a director. Gideon J. King is Executive Vice President. Loeb Holding Corporation (“LHC”), a Maryland corporation, 61 Broadway, New York, New York, 10006 is the sole stockholder of LAM and LPC. Thomas L. Kempner is its President and a director as well as its Chief Executive Officer and majority stockholder. Norman N. Mintz and Peter A. Tcherepnine are also directors. Loeb Offshore Fund, Ltd., (“LOF”) and Loeb Offshore B Fund Ltd. (“LOFB”) are each a Cayman Islands exempted company. Loeb Offshore Management, LLC (“LOM”) is a Delaware limited liability company, a registered investment adviser and is wholly owned by Loeb Holding Corporation. It is the investment adviser of LOF and LOFB. Gideon J. King and Thomas L. Kempner are Directors of LOF and LOFB and Managers of LOM. Loeb Marathon Fund (“LMF”) is a Delaware limited partnership whose general partner is LAM. Loeb Marathon Offshore Fund Ltd. (“LMOF”) is a Cayman Islands exempted company. LOM is the investment adviser of LMOF. All of the individuals named are United States citizens. None have been, within the last five years, convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) or been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding been or are subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violations with respect to such laws.

Item 3.	Source and Amount of Funds or Other Compensation

Shares of Common Stock were acquired by LAF, LPC**, LOF, LAFB and LOFB in margin accounts maintained with Bear Stearns Securities Corp.

Item 4.	Purpose of Transaction

LAF, LPC**, LOF, LAFB and LOFB (“Loeb”) have acquired shares of Common Stock for investment purposes. Loeb reserves the right, consistent with applicable law, to acquire additional securities of the Issuer (whether through open market purchases, block trades, private acquisitions, tender or exchange offers or otherwise). Loeb intends to review its investment in the Issuer on a continuing basis and may engage in discussions with management or the Board of Directors of the Issuer concerning the business and future plans of the Issuer. Depending on various factors, including, without limitation, the Issuer’s financial position and investment strategy, the price levels of the Common Stock of the Issuer, conditions in the securities markets and general economic and industry conditions, Loeb may in the future take such actions with respect to its investment in the Issuer as it deems appropriate including, without limitation, seeking Board representations, making proposals to the Issuer concerning the capitalization of the Issuer, purchasing additional Common Stock and other securities of the Issuer, selling some or all of its Common Stock, engaging in short selling of or any hedging or similar transaction with respect to the Common Stock of the Issuer or changing its intention partially or entirely with respect to any and all matters referred to in Item 4.

Item 5.		Interest in Securities of the Issuer

	(a)	The persons reporting hereby owned the following shares of Common Stock as of September 21, 2007.

			Shares of Common Stock
Loeb Arbitrage Fund			310,938
Loeb Partners Corporation**			33,748
Loeb Offshore Fund Ltd.			75,351
Loeb Arbitrage B Fund LP			99,846
Loeb Offshore B Fund Ltd.			29,328

Total			549,211

The total shares of Common Stock constitutes 6.93% of the 7,923,000 outstanding shares of Common Stock as reported by the issuer.

**Including shares of Common Stock purchased for the account of one customer of Loeb Partners Corporation as to which it has investment discretion.

(b)

See paragraph (a) above.

(c)

The following purchases of Common Stock have been made since Loeb’s previous filing related to the Issuer:

Purchases of Common Stock

Holder	Date	Shares	Average Price
Loeb Partners Corp.**	09-11-07	2,306	2.27
	09-19-07	2,275	2.31
	09-20-07	3,630	2.31
	09-21-07	611	2.30

Holder	Date	Shares	Average Price
Loeb Arbitrage Fund	09-11-07	21,377	2.27
	09-19-07	26,210	2.31
	09-20-07	26,650	2.31
	09-21-07	5,665	2.30

Holder	Date	Shares	Average Price
Loeb Offshore Fund	09-11-07	5,182	2.27
	09-19-07	7,030	2.31
	09-20-07	5,767	2.31
	09-21-07	1,372	2.30

Holder	Date	Shares	Average Price
Loeb Arbitrage B Fund LP	09-11-07	6,435	2.27
	09-19-07	11,070	2.31
	09-20-07	10,974	2.31
	09-21-07	1,818	2.30

Holder	Date	Shares	Average Price
Loeb Offshore B Fund Ltd.	09-11-07	1,897	2.27
	09-19-07	3,415	2.31
	09-20-07	2,979	2.31
	09-21-07	534	2.30

_____________________

**Including shares of Common Stock purchased for the account of one customer of Loeb Partners Corporation as to which it has investment discretion.

All reported transactions were effected on OTC.

(d)

Not Applicable.

(e)

Not Applicable.

Item 6.	Contracts, Arrangement, Understandings or Relationships with Respect to the Issuer.

	None.

Item 7.	Materials to be Filed as Exhibits.

	None.

Signature

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

		LOEB PARTNERS CORPORATION


Date: September 24, 2007	By:	/s/ Michael S. Emanuel
		Michael S. Emanuel
		Senior Vice President

		LOEB ARBITRAGE FUND
		By: LOEB ARBITRAGE MANAGEMENT, INC., G.P.


Date: September 24, 2007	By:	/s/ Michael S. Emanuel
		Michael S. Emanuel
		Vice President

		LOEB OFFSHORE FUND LTD.


Date: September 24, 2007	By:	/s/ Michael S. Emanuel
		Michael S. Emanuel
		Vice President

		LOEB ARBITRAGE B FUND LP
		By: LOEB ARBITRAGE B MANAGEMENT, LLC, G.P.


Date: September 24, 2007	By:	/s/ Michael S. Emanuel
		Michael S. Emanuel
		Vice President

		LOEB OFFSHORE B FUND LTD.



Date: September 24, 2007	By:	/s/ Michael S. Emanuel
		Michael S. Emanuel
		Vice President

GENSYM CORP SC 13D/A