Proper two-sided restriction semigroups and partial actions

Proper Restriction Semigroups – Semidirect Products and W -products

Fountain and Gomes have shown that any proper left ample semigroup embeds into a so-called W -product, which is a subsemigroup of a reverse semidirect product T ⋉ Y of a semilattice Y by a monoid T , where the action of T on Y is injective with images of the action being order ideals of Y. Proper left ample semigroups are proper left restriction, the latter forming a much wider class. The aim o...

Proper Covers of restriction Semigroups and W-Products

Each factor semigroup of a free restriction (ample) semigroup over a congruence contained in the least cancellative congruence is proved to be embeddable into a W -product of a semilattice by a monoid. Consequently, it is established that each restriction semigroup has a proper (ample) cover embeddable into such a W -product.

Partial Actions of Inverse and Weakly Left E-ample Semigroups

We introduce partial actions of weakly left E-ample semigroups, thus extending both the notion of partial actions of inverse semigroups and that of partial actions of monoids. Weakly left E-ample semigroups arise very naturally as subsemigroups of partial transformation semigroups which are closed under the unary operation α 7→ α, where α is the identity map on the domain of α. We investigate t...

Restriction and Ehresmann Semigroups

Inverse semigroups form a variety of unary semigroups, that is, semigroups equipped with an additional unary operation, in this case a 7→ a−1. The theory of inverse semigroups is perhaps the best developed within semigroup theory, and relies on two factors: an inverse semigroup S is regular, and has semilattice of idempotents. Three major approaches to the structure of inverse semigroups have e...

Constructing Homomorphisms through E-unitary Inverse Semigroups via Partial Group Actions and Semilattice Actions