Article 20 excludes the application of the doctrine of "renvoi" in relation to contracts. The system of renvoi is an attempt to achieve that end. However its rejection of renvoi is not seen as completely definitive. The basic criticism of renvoi is that it can lead to an endless circle. Most U.S. states frown upon renvoi in a choice of law situation. A single renvoi forum always refers to the other law's choice of law rules. Later, Duchamp made a positive version, titled "Mirrorical Return" ("Renvoi miroirique"; 1964).