1. G. Birkhoff, Lattice Theory, American Mathematical Society, New York (1940).
2. Yu. L. Ershov, Theory of Enumerations, 1, Novosibirsk (1969).
3. Yu. L. Ershov, "Constructive models," in: Selected Topics in Algebra and Logic, Novosibirsk (1973), pp. 111–130.
4. A. I. Mal'tsev, Algorithms and Recursive Functions [in Russian], Nauka (1965).
5. A. I. Mal'tsev, "Constructive algebras," UMN,16, No. 3, 3–60 (1961).