It is possible that the same matter is governed by a treaty and by customary international law, and that these rules coexist. In general, if there is more than one applicable rule, the choice between them should be made through the use of established principles of interpretation, such as.B. applying the maxims lex specialis derogat legi generali and lex posterior derogat legi priori (UN ITC “Fragmentation of international law: difficulties arising from the diversification and expansion of international law” (2006) GAOR 61st session Supp 10, 400, c. 408-18; Interpretation in international law). Normally, the treaty will be the rule of lex specialis and will prevail over inconsistent customary international law. It may be different if, after the conclusion of the treaty, a new norm of customary international law emerges. Then the question may arise as to whether custom prevails over the contract.