[1] BIRKHOFF G.: Lattice theory. 3. ed. Providence 1967. MR 0227053 | Zbl 0153.02501

[2] DRAŠKOVIČOVÁ H.: Independence of equational classes. Mat. Čas. 23, 1973, 125-135. MR 0327617 | Zbl 0264.08001

[3] DRAŠKOVIČOVÁ H.: Malcev type conditions for two varieties. Math. Slovaca. 27, 1977, 177-180. MR 0457326

[4] GRÄTZER G., LAKSER H., PLONKA J.: Joins and diгect products of equational classes. Canad. Math. Bull. 12, 1969, 741-744. MR 0276160