1. S. S. Goncharov and V. P. Dobritsa, "An example of a constructive Abelian group with nonconstructivizable reduced subgroup," 4th All-Union Conf. on Math. Logic, Kishinev (1976), p. 33.
2. N. G. Khisamiev, "Strongly constructive Abelian P - groups," Algebra Logika,22, No. 2, 198–217 (1983).
3. A. I. Mal'tsev, "Positive and negative enumerations," Dokl. Akad. Nauk SSSR,160, No. 2, 278–280 (1965).
4. Yu. L. Ershov, Problems of Solubility and Constructive Models [in Russian], Nauka, Moscow (1980).
5. Yu. L. Ershov, Enumeration Theory [in Russian], Nauka, Moscow (1977).