A basis of identities Σ for a semigroup S is a set of identities satisfied by S from which all other identities of S can be derived. The basis Σ is said to be irredundant (or irreducible) if no proper subset of Σ is a basis for the identities of S. If the basis Σ is finite, then it is always possible to extract an irredundant basis, however if Σ is infinite then it is conceivable that no irredu...

One of the most natural approaches to the study of regular semigroups is to impose restrictions on the partial ordering of their idempotents (erg/^e/—jfe==e). The principal object of this note is to describe the structure of the classes of regular semigroups whose idempotents form a tree or a unitary tree, respectively (see Definition 1). We determine, among other things, a complete set of inva...

With an aim to developing expressive language theoretical tools applicable to inverse semigroup languages, that is, subsets of inverse semigroups, this paper explores the language theory of finite labeled birooted trees: Munn’s birooted trees extended with vertex labeling. To this purpose, we define a notion of finite state birooted tree automata that simply extends finite state word automata s...

Two classes of finite Mealy automata (automata without branches, slowmoving automata) are considered in this article. We study algebraic properties of transformations defined by automata of these classes. We consider groups and semigroups defined by automata without branches.

In this paper, all semigroups are assumed to be finite unless otherwise stated. If H is a pseudovariety of groups (that is, a class of groups closed under formation of finite direct products, subgroups and quotients groups), then it is natural to define a group to be Hsolvable if it has a subnormal series each of whose quotients belongs to H. For instance a group is solvable in the classical se...

We consider rewriting as a tool for solving identity problems in varieties of idempotent semigroups. It is known that there exist finite canonical term rewrite systems and finite canonical word rewrite systems for only a very limited number of those varieties. We present a finite canonical conditional word rewrite system for a particular variety in which the classical approaches cannot be appli...

The finite generation and presentation of Schützenberger products of semigroups are investigated. A general necessary and sufficient condition is established for finite generation. The Schützenberger product of two groups is finitely presented as an inverse semigroup if and only if the groups are finitely presented, but is not finitely presented as a semigroup unless both groups are finite. 200...

in the present paper for a large family of topological semigroups, namely foundation semigroups, for which topological groups and discrete semigroups are elementary examples, it is shown that ?(s) is the dual of a function algebra.

The paper shows how some semigroup-theory methods can be used in automata problems. The theory of automata is closely connected with the theory of semigroups (or, to be more exact, with the theory of representations of semigroups by transformations). The concept of automaton without outputs is equivalent to the concept of representa­ tion of free semigroup by transformations. If we consider eve...