Search

A monoid is pseudo-complex if the semigroup variety it generates has uncountably many subvarieties, while the monoid variety it generates has only finitely many subvarieties. The smallest pseudo-complex monoid currently known is of order seven. The present article exhibits a pseudo-complex monoid of order six and shows that every smaller monoid is not pseudo-complex. Consequently, minimal pseudo-complex monoids are of order six. [ABSTRACT FROM AUTHOR]

A generalized hypersubstitution of type τ = (n) is a function which takes the n-ary operation symbol f to the term of the same type σ(f ) which does not necessarily preserve the arity. Let HypG(n) be the set of all these generalized hypersubstitutions of type (n). The set HypG(n) with a binary operation and the identity generalized hypersubstitution forms a monoid. The objective of this paper is to study Green’s relations on the set of all regular elements of HypG(n).

The set of all cancellable elements of the lattice of semigroup varieties has recently been shown to be countably infinite. But the description of all cancellable elements of the lattice MON of monoid varieties remains unknown. This problem is addressed in the present article. The first example of a monoid variety with modular but non-distributive subvariety lattice is first exhibited. Then a necessary condition of the modularity of an element in MON is established. These results play a crucial role in the complete description of all cancellable elements of the lattice MON . It turns out that there are precisely five such elements. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the lattice of subvarieties of the ai-semiring variety defined by the additional identities

In this paper we consider mappings σ which map the binary operation symbol f to the term σ (f) which do not necessarily preserve the arity. These mapping are called generalized hypersubstitutions of type τ = (2) and we denote the set of all these generalized hypersubstitutions of type τ = (2) by HypG (2). The set HypG(2) together with a binary operation defined on this set and the identity generalized hypersubstitution which maps f to the term f(x1, x2) forms a monoid. In this paper, we determine all maximal completely regular submonoids of this monoid.

An exclusion variety is a variety that is maximal with respect to not containing some semigroup. It is shown that if the bases of all exclusion varieties for some periodic semigroup S are known, then the bases of exclusion varieties for the monoid S1 can be computed. [ABSTRACT FROM AUTHOR]