1. Addison, J.W.: On some points of the theory of recursive functions. Ph.D. Thesis, University of Wisconsin (1954)
2. Addison, J.W.: Separation principles in the hierarchies of classical and effective descriptive set theory. Fundamenta Methematicae 46, 123–135 (1959)
3. Boolos, G.S., Burgess, J.P., Jeffrey, R.C.: Computability and logic. Cambridge University Press, Cambridge (1974)
4. Ceitin, G.: Algorithmic operators in constructive metric spaces. Trudy Mat. Inst. Steklov. 67, 295–361 (1962)
5. Davis, M.: Relatively recursive functions and the extended Kleene hierarchy. In: Proceedings of the International Congress of Mathematicians, Cambridge, Mass, p. 723 (1950)