[1] I. Chajda: Tolerance trivial algebras and varieties. Acta Sci. Math. (Szeged), 46 (1983), 35-40. MR 0739020 | Zbl 0534.08001

[2] I. Chajda: Recent results and trends in tolerances on algebras and varieties. Colloq. Math. Soc. J. Bolyai 28., Finite algebra and multiple-valued logic, Szeged (Hungary) 1979,N orth-Holland 1981, 69-95. MR 0648608

[3] I. Chajda B. Zelinka: Tolerances on lattices. Časopis pěst. matem. 99 (1974), 394-399. MR 0360380

[4] A. I. Maľcev: On the general theory of algebraic systems. (Russian), Matem. Sborník 35 (1954), 3-20. MR 0065533

[5] B. Zelinka: Tolerance in algebraic structures I, II. Czechoslovak Math. J. 20 (1970), 240-256; 25(1975), 175-178. MR 0457323