A Special Congruence Lattice of a Regular Semigroup
Acta mathematica Universitatis Comenianae, Tome 76 (2007) no. 2
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Let S be a regular semigroup and C its lattice of congruences. We consider the sublattice L of C generated by s -the least group, t -the greatest idempotent pure, m -the greatest idempotent separating and b -the least band congruence on S . To this end, we study the following special cases: (1) any three of these congruences generate a distributive lattice, (2) L is distributive, (3) the restriction of the K -relation to L is a congruence and (4) a further special case. In each of these instances, we provide several characterizations. Our basic concept is that of a c -triple which represents an abstraction of ( L ; K | L , T | L ).