Characterizing pure, cryptic and Clifford inverse semigroups
An inverse semigroup is pure if , , implies ; it is cryptic if Green’s relation on is a congruence; it is a Clifford semigroup if it is a semillatice of groups. We characterize the pure ones by the absence of certain subsemigroups and a homomorphism from a concrete semigroup, and determine minimal nonpure varieties. Next we characterize the cryptic ones in terms of their group elements and also by a homomorphism of a semigroup constructed in the paper. We also characterize groups and...