[2] Clifford A. H., Preston G. B.:
The algebraic theory of semigroups. Vol. I. Am. Math. Soc., 1961.
MR 0132791 |
Zbl 0111.03403
[6] Pondělíček B.:
Modularity and distributivity of tolerance lattices of commutative inverse semigroups. Czech. Math. J., 35 (110), 1985, 146-157.
MR 0779342