On power commutative semigroups.
Let be a regular semigroup and be the set of its idempotents. We call the sets and one-sided sandwich sets and characterize them abstractly where . For such that , , we call the sandwich set of . We characterize regular semigroups in which all (or all are right zero semigroups (respectively are trivial) in several ways including weak versions of compatibility of the natural order. For every , we also define as the set of all idempotets such that, for any congruence on...