[1] I. Chajda: Lattices of compatible relations. Arch. Math. (Brno) 13 (1977), 89-96. MR 0463081 | Zbl 0372.08002

[2] I. Chajda B. Zelinka: Lattices of tolerances. Čas. pěst. mat. 102 (1977), 10-24. MR 0450152

[3] A. H. Clifford G. B. Preston: The algebraic theory of semigroups. Amer. Math. Soc., Providence, R. I. Vol. I (1961), Vol. II (1967).

[4] B. Pondělíček: Modularity and distributivity of tolerance lattices of commutative separative semigroups. Czech. Math. J. 35 (110) (1985), 333-337. MR 0787135

[5] H. Hamilton: Modularity and distributivity of the congruence lattice of a commutative separative semigroup. Math. Japonica 27 (1982), 581-589. MR 0675554 | Zbl 0492.20042

[6] O. Ore: Structures and group theory II. Duke Math. J. 4 (1938), 247-269. MR 1546048 | Zbl 0020.34801