1. A set of postulates for the foundation of logic;Church, Alonzo;Ann. of Math. (2),1932
2. M. Davis, On the theory of recursive unsolvability, Ph.D. thesis (typewritten), Princeton University, 1950.
3. \bysame, Relatively recursive functions and the extended Kleene hierarchy, Proceedings of the International Congress of Mathematicians (Cambridge, Mass., U.S.A., Aug. 30-Sept. 6, 1950), 1952, vol. 1, p. 723.
4. S. C. Kleene, On notation for ordinal numbers, J. Symbolic Logic vol. 3 (1938) pp. 150-155.
5. Recursive predicates and quantifiers;Kleene, S. C.;Trans. Amer. Math. Soc.,1943