 Apart from the truth-theoretic axioms, KF comprises all axioms of PA and all induction axioms involving the truth predicate. The system is credited to Feferman on the basis of two lectures for the Association of Symbolic Logic, one in 1979 and the second in 1983, as well as in subsequent manuscripts. Feferman published his version of the system under the label Ref(PA) (‘weak reflective closure of PA’) only in 1991, after several other versions of KF had already appeared in print (e.g., Reinhardt 1986, Cantini 1989, who both refer to this unpublished work by Feferman).