1. V. A. Gorbunov, "Coverings in lattices of quasivarieties and independent axiomatizability," Algebra Logika,10, No. 5, 507–548 (1977).
2. V. A. Gorbunov, "Quasiidentities of two-element algebras," Algebra Logika,22, No. 2, 121–127 (1983).
3. A. I. Mal'tsev, Algebraic Systems [in Russian], Nauka, Moscow (1970).
4. A. I. Mal'tsev, "On the general theory of algebraic systems," Mat. Sb.,35, No. 1, 3–20 (1954).
5. G. Birkhoff, "On the structure of abstract algebras," Proc. Cambridge Phil. Soc.,31, 433–454 (1935).