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:
"""
Exhibit A JOINT FILING AGREEMENT Pursuant to and in accordance with the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder (the "Exchange Act") the undersigned hereby agree to the joint filing of Clarus IV-A, L.P., Clarus IV-B, L.P., Clarus IV-C, L.P., Clarus IV-D, L.P., Clarus IV GP, L.P., Blackstone Clarus GP L.P., Blackstone Clarus GP L.L.C., Blackstone Holdings II L.P., Blackstone Holdings I/II GP L.L.C., The Blackstone Group Inc., Blackstone Group Management L.L.C. and Stephen A. Schwarzman, on behalf of each of them of any filing required by such party under Section 13 of the Exchange Act or any rule or regulation thereunder (including any amendment, restatement, supplement, and/or exhibit thereto) with respect to securities of Galera Therapeutics, Inc., a Delaware corporation, and further agree to the filing, furnishing, and/or incorporation by reference of this Agreement as an exhibit thereto. Each of them is responsible for the timely filing of such filings and any amendments thereto, and for the completeness and accuracy of the information concerning such person contained therein; but none of them is responsible for the completeness or accuracy of the information concerning the other persons making the filing, unless such person knows or has reason to believe that such information is inaccurate. This Agreement shall remain in full force and effect until revoked by any party hereto in a signed writing provided to each other party hereto, and then only with respect to such revoking party. This Agreement may be executed in any number of counterparts all of which taken together shall constitute one and the same instrument. IN WITNESS WHEREOF, the undersigned hereby execute this Agreement this 14t h day of February 2020. CLARUS IV-A, L.P. By: Clarus IV GP, L.P., its general partner By: Blackstone Clarus GP L.P., its general partner By: Blackstone Clarus GP L.L.C., its general partner By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer CLARUS IV-B, L.P. By: Clarus IV GP, L.P., its general partner By: Blackstone Clarus GP L.P., its general partner By: Blackstone Clarus GP L.L.C., its general partner By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer CLARUS IV-C, L.P. By: Clarus IV GP, L.P., its general partner By: Blackstone Clarus GP L.P., its general partner By: Blackstone Clarus GP L.L.C., its general partner By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer [Galera Therapeutics, Inc. - Joint Filing Agreement] CLARUS IV-D, L.P. By: Clarus IV GP, L.P., its general partner By: Blackstone Clarus GP L.P., its general partner By: Blackstone Clarus GP L.L.C., its general partner By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer CLARUS IV GP, L.P. By: Blackstone Clarus GP L.P., its general partner By: Blackstone Clarus GP L.L.C., its general partner By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer BLACKSTONE CLARUS GP L.P. By: Blackstone Clarus GP L.L.C., its general partner By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer BLACKSTONE CLARUS GP L.L.C. By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer BLACKSTONE HOLDINGS II L.P. By: Blackstone Holdings I/II GP L.L.C., its general partner By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer BLACKSTONE HOLDINGS I/II GP L.L.C. By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer THE BLACKSTONE GROUP INC. By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer [Galera Therapeutics, Inc. - Joint Filing Agreement] BLACKSTONE GROUP MANAGEMENT L.L.C. By: /s/ John G. Finley Name: John G. Finley Title: Chief Legal Officer /s/ Stephen A. Schwarzman Stephen A. Schwarzman [Galera Therapeutics, Inc. - Joint Filing Agreement]
"""

Extract the exact clause related to "Source Code Escrow" from the excerpt above.