The equational theory of paramedial cancellation groupoids
The existence of upper semicomplements in lattices of primitive classes
The exocenter and type decomposition of a generalized pseudoeffect algebra
We extend the notion of the exocenter of a generalized effect algebra (GEA) to a generalized pseudoeffect algebra (GPEA) and show that elements of the exocenter are in one-to-one correspondence with direct decompositions of the GPEA; thus the exocenter is a generalization of the center of a pseudoeffect algebra (PEA). The exocenter forms a boolean algebra and the central elements of the GPEA correspond to elements of a sublattice of the exocenter which forms a generalized boolean algebra. We extend...
The finite basis problem in the pseudovariety joins of aperiodic semigroups with groups.
The finite basis question for semigroups of order less than six.
The finiteness of a base of indentities for fiveelement monoids
The free one-generated left distributive algebra: basics and a simplified proof of the division algorithm
The left distributive law is the law a· (b· c) = (a·b) · (a· c). Left distributive algebras have been classically used in the study of knots and braids, and more recently free left distributive algebras have been studied in connection with large cardinal axioms in set theory. We provide a survey of results on the free left distributive algebra on one generator, A, and a new, simplified proof of the existence of a normal form for terms in A. Topics included are: the confluence of A, the linearity...
The Galois correspondence between subvariety lattices and monoids of hpersubstitutions
Denecke and Reichel have described a method of studying the lattice of all varieties of a given type by using monoids of hypersubstitutions. In this paper we develop a Galois correspondence between monoids of hypersubstitutions of a given type and lattices of subvarieties of a given variety of that type. We then apply the results obtained to the lattice of varieties of bands (idempotent semigroups), and study the complete sublattices of this lattice obtained through the Galois correspondence.
The globals of pseudovarieties of ordered semigroups containing and an application to a problem proposed by Pin
Given a basis of pseudoidentities for a pseudovariety of ordered semigroups containing the 5-element aperiodic Brandt semigroup , under the natural order, it is shown that the same basis, over the most general graph over which it can be read, defines the global. This is used to show that the global of the pseudovariety of level of Straubing-Thérien’s concatenation hierarchy has infinite vertex rank.
The globals of pseudovarieties of ordered semigroups containing B2 and an application to a problem proposed by Pin
Given a basis of pseudoidentities for a pseudovariety of ordered semigroups containing the 5-element aperiodic Brandt semigroup B2, under the natural order, it is shown that the same basis, over the most general graph over which it can be read, defines the global. This is used to show that the global of the pseudovariety of level 3/2 of Straubing-Thérien's concatenation hierarchy has infinite vertex rank.
The groupoid of 0-reduced varieties of Semigroups (n).
The hereditary pure monoids.
The ideal structure of simple ternary algebras
The join of equational theories
The join of the pseudovarieties of idempotent semigroups and locally trivial semigroups.
The lattice of equational theories. Part I: Modular elements
The lattice of equational theories. Part II: The lattice of full sets of terms
The lattice of equational theories. Part III: Definability and automorphisms
The lattice of equational theories. Part IV: Equational theories of finite algebras
The lattice of subautomata of an automaton: A survey.