1. Modèles de l'Arithmétique, ed. by K. McAloon, Astérisque 73(1980).
2. A note on the hyperarithmetic hierarchy;Enderton;J. Symbolic Logic,1970
3. Systems of predicative analysis;Feferman;J. Symbolic Logic,1964
4. H. Friedman, Some systems of second order arithmetic and their use, Proceedings of the International Congress of Mathematicians (Vancouver 1974), vol. 1, Canadian Mathematical Congress, 1975, pp. 235–242.
5. Systems of second order arithmetic with restricted induction (abstracts);Friedman;J. Symbolic Logic,1976