Congruences on an ample semigroup S are investigated. For any admissible congruence ρ
ρ on S, the minimum σ _ ρ σ ρ (the maximum μ _ ρ μ ρ) admissible congruence on S whose …

This is the first of two articles studying the structure of left adequate and, more generally, of
left Ehresmann monoids. Motivated by a careful analysis of normal forms, we introduce here …

Classes of (left) restriction semigroups arise from partial transformation monoids and form a
wider class than inverse semigroups. Firstly, we produce a presentation of the Szendrei …

For an admissible congruence γ γ on an ample semigroup S, the minimum admissible
congruence γ _t γ t whose trace is tr γ tr γ has been determined by the author, and Fountain …

An appropriate generalization of the notion of permissible sets of inverse semigroups is
found within the class of weakly ample semigroups that allows us to introduce the notion of …

We prove a structure result on proper extensions of two-sided restriction semigroups in
terms of partial actions, generalizing respective results for monoids and for inverse …

The generalized prefix expansion of inverse semigroups, presented by Lawson, Margolis
and Steinberg, is suitably modified to define an expansion for weakly left ample semigroups …

PROPER COVERS OF AMPLE MONOIDS Page 1 Proceedings of the Edinburgh Mathematical
Society (2006) 49, 277–289 c DOI:10.1017/S0013091504000070 Printed in the United …

Generalized restriction P-restriction semigroups are common generalizations of restriction
semigroups and generalized inverse*∗-semigroups. Gomes and Szendrei (resp. Ohta and …

In this paper, we describe the structure of proper left GC-lpp semigroups. Our main result not
only generalizes a result of Takizawa on E-unitary-unipotent semigroups but also those of …