Eilenberg has shown that there is a one-to-one correspondence between varieties of finite monoids and varieties of recognizable languages. In this paper, we give a description of a variety of languages close to the class of piecewise testable languages considered by I. Simon. The corresponding variety of monoids is the variety of J -trivial monoids with commuting idempotents. This result is the...

Ehresmann monoids form a variety of biunary monoids, that is, monoids equipped with two basic unary operations, the images of which coincide and form a semilattice of projections. The monoid of binary relations BX on any setX with unary operations of domain and range is Ehresmann. Inverse monoids, regarded as biunary submonoids of BX via the Wagner-Preston representation theorem, are therefore ...

We give an algebraic characterization of the tree languages that are defined by logical formulas using certain Lindström quantifiers. An important instance of our result concerns first-order definable tree languages. Our characterization relies on the usage of preclones, an algebraic structure introduced by the authors in a previous paper, and of the block product operation on preclones. Our re...

We study algebraic properties of the Brandt λ-extensions of monoids with zero and non-trivial homomorphisms between the Brandt λ-extensions of monoids with zero. We introduce finite, compact topological Brandt λextensions of topological semigroups and countably compact topological Brandt λ-extensions of topological inverse semigroups in the class of topological inverse semigroups and establish ...

Length preserving morphisms and inverse of substitutions are two wellstudied operations on regular languages. Their connection with varieties generated by power monoids was established independently by Reutenauer and Straubing in 1979. More recently, an ordered version of this theory was proposed by Polák and by the authors. In this paper, we present an improved version of these results and obt...

We describe the use of symbolic algebraic computation allied with AI search techniques, applied to the problem of the identification, enumeration and storage of all monoids of order 9 or less. Our approach is novel, using computer algebra to break symmetry and constraint satisfaction search to find candidate solutions. We present new results in algebraic combinatorics: up to isomorphism and ant...

On Graphs With A Given Endomorphism Monoid Benjamin Shemmer Hedrĺın and Pultr proved that for any monoid M there exists a graph G with endomorphism monoid isomorphic to M. We will give a construction G(M) for a graph with prescribed endomorphism monoid M. Using this construction we derive bounds on the minimum number of vertices and edges required to produce a graph with a given endomorphism mo...

Solving equations in algebraic structures is a fundamental task in mathematics. Here we tackle this problem for free partially commutative monoids with involution and for graph groups, which are free groups with a partial commutation relation between generators. Basic algebraic structures involving partial commutations are free partially commutative monoids (also known as trace monoids). They w...

Abstract It is well known that the set of isomorphism classes extensions groups with abelian kernel characterized by second cohomology group. In this paper we generalise characterization to a natural class monoids, cosetal extensions. An extension "Equation missing" if for all $$g,g' \in G$$ <mml:mr...