system: You are a contract-analysis assistant performing a span-extraction task. You are given an excerpt from a commercial contract and the name of a clause type to locate within it.

Return the exact text of the requested clause, copied verbatim from the excerpt — identical wording and punctuation, with no paraphrasing, summarising, explanation, or added commentary.

The excerpt is one window of a much longer contract and often will not contain the requested clause. If the requested clause does not appear in this excerpt, respond with exactly: Not found.

Output only the extracted clause text, or the exact string `Not found.` — nothing else.

user: Contract excerpt:
"""
of which together constitute a single agreement. In proving this Agreement, it will not be necessary to produce or account for more than one counterpart signed by the party with respect to which proof is sought. This Agreement is the sole understanding and agreement of the parties with respect to its subject matter and supersedes all other such prior or contemporaneous oral and written agreements and understandings. Signed, sealed and delivered by a duly authorized representative of each party hereto as of the date first written above. THE BUTLER COMPANY BIOPURE CORPORATION By: By: -------------------------------- -------------------------------- Andrew W. Wright, Title: Vice President, Veterinary ----------------------------- Products Address: Address: 11 Hurley Street --------------------------- Cambridge, MA 02141 Telecopy No.: (617) 234-6507 --------------------------- --------------------------- 16 EXHIBIT A BIOPURE CORPORATION Oxyglobin(R) Brand Products Price List (Introductory Promotional Pricing*) Each Box contains two 125 ml bags of Oxyglobin(R) Brand Veterinary Product. Retail Price Retail Price Per Bag ------------ -------------------- 1 Box of 2 Bags $279.90 $139.95 2 Boxes of 2 Bags $499.80 $124.95 3 Boxes of 2 Bags $749.70 $124.95 4 Boxes of 2 Bags $999.60 $124.95 5 Boxes of 2 Bags $1099.50 $109.95 - ---------- *May be changed with 30 days written notice. Effective Date: January 5, 1999 17 EXHIBIT B OXYGLOBIN(R) BUSINESS PLAN FISCAL YEAR 1999 (Nov 1, 1998 through Oct 31, 1999) AGENT: THE BUTLER COMPANY FY: 1999 QUARTERLY GOALS 1st Quarter (Nov 1 - Jan 31): N/A units 2nd Quarter (Feb 1 - Apr 30): 3,500 units 3rd Quarter (May 1 - Jul 31): 7,000 units 4th Quarter (Aug 1 - Oct 31): 8,400 units Fiscal Year Total: 18,900 units Unit = 1 Bag of Oxyglobin Solution 125 ml PROMOTIONAL ACTIVITIES Sales Meetings: Anticipated Dates ______________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ Ride Withs (# Per Quarter) 1st Qtr ____________ 2nd Qtr ____________ 3rd Qtr ____________ 4th Qtr ____________ Total for Year ____________ 18 Conferences with Display of Biopure Product:____________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ Agent Monthly Flyer, Catalog, Other ____________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ Other Activities (Dinner Meeting Support, Advertising, Mailings, etc)___________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ THE BUTLER COMPANY: BIOPURE CORPORATION: - ---------------------------- ---------------------------- Name Name - ---------------------------- ---------------------------- Title Title - ---------------------------- ---------------------------- Date Date
"""

Extract the exact clause related to "Irrevocable Or Perpetual License" from the excerpt above.