A monoid is called special if it admits a presentation in which all defining relations are of the
form w= 1. Every group is special, but not every monoid is special. In this article, we describe …

This paper studies the classes of semigoups and monoids with context-free and
deterministic context-free word problem. First, some examples are exhibited to clarify the …

The subject matter of this thesis is combinatorial semigroup theory. It includes material, in no
particular order, from combinatorial and geometric group theory, formal language theory …

The Diophantine problem for a monoid M is the decision problem to decide whether any
given system of equations has a solution in M. In this short note, we give a simple example …

We study the language-theoretic properties of the word problem, in the sense of Duncan &
Gilman, of weakly compressible monoids, as defined by Adian & Oganesian. We show that if …

We introduce and study a strong “thin triangle” condition for directed graphs, which
generalises the usual notion of hyperbolicity for a metric space. We prove that finitely …

This paper makes a comprehensive survey of results relating to finite Rees index for
semigroups. In particular, we survey of the state of knowledge on whether various finiteness …

A monoid is said to be special if it admits a presentation in which all defining relations are of
the form $ w= 1$. Groups are familiar examples of special monoids. This article studies the …

This article studies the properties of word-hyperbolic semigroups and monoids, that is, those
having context-free multiplication tables with respect to a regular combing, as defined by …

This paper studies decision problems for semigroups that are word-hyperbolic in the sense
of Duncan and Gilman. A fundamental investigation reveals that the natural definition of a …