1. The logic of provability;Boolos;Amer. Math. Monthly,1984
2. Truth and paradox;Gupta;J. Philos. Logic,1982
3. Functional interpretation of bar induction by bar recursion;Howard;Compositio Math.,1968
4. A survey of proof theory;Kreisel;J. Symbolic Logic,1968
5. Outline of a theory of truth;Kripke;J. Philosophy,1975