87. Performance.

Every treaty1 in force is binding upon the parties to it and must be performed by them in good faith2. A party may not invoke the provisions of its internal law as justification for its failure to perform a treaty3. The obligation under a treaty depends upon international law exclusively, and although the implementation of many treaties calls for changes in the internal law of the parties, this is within their contemplation from the outset, and the entry into force of the treaty may be and often is expressly made dependent upon the procurement of the necessary changes in