 Jurisprudential developments in the American law of perjury have revolved around the facilitation of "perjury prosecutions and thereby enhance the reliability of testimony before federal courts and grand juries".With that goal in mind, Congress has sometimes expanded the grounds on which an individual may be prosecuted for perjury, with section 1623 of the United States Code recognizing the utterance of two mutually incompatible statements as grounds for perjury indictment even if neither can unequivocally be proven false.However, the two statements must be so mutually incompatible that at least one must necessarily be false; it is irrelevant whether the false statement can be specifically identified from among the two.