1. Yu. L. Ershov, Theory of Enumerations [in Russian], Part 1, Novosibirsk Univ., Novosibirsk (1969).
2. A. I. Mal'tsev, ?Positive and negative enumerations,? Dokl. Akad. Nauk SSSR,160, No. 2, 278?280 (1965).
3. H. Putnam, ?Trial and error predicates and the solution to a problem of Mostowski,? J. Symbolic Logic,30, No. 1, 49?57 (1965).
4. V. V. V'yugin, ?Discrete classes of recursively enumerable sets,? Algebra Logika,11, No. 3, 243?256 (1972).
5. Yu. L. Ershov, ?Computable enumerations,? Algebra Logika,7, No. 5, 71?99 (1968).