1. Yu. L. Ershov, “On a hierarchy of sets. I,” Alg. i Log.,7, No. 1, 47–74 (1968).
2. Yu. L. Ershov, “On a hierarchy of sets. II,” Alg. i Log.,7, No. 4, 15–47 (1968).
3. Yu. L. Ershov, “Completely numbered sets,” Sibir. Matem. Zh.,10, No. 5, 1048–1067 (1969).
4. A. I. Mal'tsev, Algorithms and Recursive Functions [in Russian], Nauka (1965).
5. H. Rogers, Theory of Recursive Functions and Effective Computability, McGraw-Hill (1967).