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:
"""
the date of termination of the Contract. 16.3 In case the SENDER fails to appear to the liquidation, or if there is not an agreement of the same within the term previously mentioned, the SENDER expressly authorizes ECOPETROL to proceed with the liquidation in one (1) month term. 16.4 The following shall be expressly stated in the minutes of liquidation: 16.5 Upon liquidation of the Contract, the SENDER shall pay ECOPETROL any Fees or any amount of money owed or resulting from the final liquidation of the same, after making any deduction that may be applicable. h) The termination in advance of this Contract shall not release the SENDER from the obligations that survive the termination of the Contract, especially that related with the payment of the Fee pending of payment and the payment of the penal clause. In the event of termination in advance of the Contract, the SENDER shall have a sixty (60) day term following the issuance of the corresponding invoice by ECOPETROL to pay the amount of any overdue fees. a) The statement regarding the performance of the obligation undertaken by each of the Parties (or from ECOPETROL if the liquidation is unilateral) derived from the execution of the Contract; and b) Any agreements, settlements and transactions reached by the Parties to settle any differences that may have arisen and to obtain the good standing and release of any obligations. 10 CLAUSE SEVENTEENTH AUTHORIZED REPRESENTATIVES FROM THE PARTIES 17.1 Each of the Parties shall notify to the other in writing, before the commencement of the execution of this Contract the name, position, addresses, institutional electronic mails and telephone numbers of the person(s) authorized to represent it. Likewise, any change of these representatives shall be notified in writing. 17.2 Any instruction or notification addressed to the representative designated in the manner previously established shall be considered as addressed to the respective Party. CLAUSE EIGHTEENTH AMENDMENTS 18.1 Any amendment, clarification or addition to the conditions stipulated in the Contract hereof, shall be in writing, in documents subscribed by the authorized representatives by the Parties. CLAUSE NINETEENTH ASSIGNMENT 19.1 The SENDER shall not assign totally or partially the Contract hereof, without the previous written consent by ECOPETROL. 19.2 The assignee shall assume all rights and obligations in the same terms established hereto. 19.3 The assignment may be authorized by ECOPETROL, when the SENDER sufficiently demonstrates to ECOPETROL that: a) The assignee is a legal person duly organized and the duration of the same shall not be less that the term of the Contract and three (3) more years. b) The assignee has an adequate financial capacity to meet the obligations derived from the Contract assigned. c) The assignee has Crude of its own/production. d) The assignee provides and adequate and acceptable Bond payment to ECOPETROL for the fulfillment of the obligations derived from the Contract. 19.4 ECOPETROL may assign the Contract without the authorization from the SENDER. CLAUSE TWENTIETH LICENSES, PERMITS AND AUTHORIZATIONS 20.1 The Parties are obliged to have or obtain all required licenses, permits and authorizations for the execution of the purpose of the Contract. Each Party shall be individually liable for all those risks, fines, sanctions or damage caused as a result of the absence of any license, permit or authorization that is obliged to obtain and therefore shall defend and hold the other Party harmless before any authorities, judges and third parties. 11 CLAUSE TWENTY-FIRST EXCLUSION OF THE LABOR RELATION 21.1 The Parties do not assume any labor relationship with personnel that, by virtue of the Contract, are assigned to the other Party for the appropriate execution of the same. All future or present obligations resulting from the relations of the Parties with its personnel shall be exclusively borne by the Party involved, and therefore, each Party assumes full responsibility concerning compliance with labor regulations and social security and shall hold the other Party harmless against any claim in connection with any violation to the mentioned regulations. CLAUSE TWENTY-SECOND INDEMNITY 22.1 ECOPETROL is obliged to protect, indemnify and hold the SENDER harmless against any loss, cost or damage to be caused or derived from, or related with the breaching of the Contract by ECOPETROL, save the same are caused by Excusable Events. 22.2 The SENDER is obliged to protect, indemnify and hold ECOPETROL harmless and its parent, affiliates and subsidiaries, and the directors, employees, agents and representatives of ECOPETROL, and of its affiliates and subsidiaries against any loss, cost or damage to be caused or
"""

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