-systems of unary algebras. II: Maximal and minimal subalgebras of the direct products of unary algebras
Radical decompositions of semiheaps
Semiheaps are ternary generalisations of involuted semigroups. The first kind of semiheaps studied were heaps, which correspond closely to groups. We apply the radical theory of varieties of idempotent algebras to varieties of idempotent semiheaps. The class of heaps is shown to be a radical class, as are two larger classes having no involuted semigroup counterparts. Radical decompositions of various classes of idempotent semiheaps are given. The results are applied to involuted I-semigroups, leading...
Range sets and partition sets in connection with congruences and algebraic invariants.
Rees ideal algebras
We describe algebras and varieties for which every ideal is a kernel of a one-block congruence.
Refinement Monoids, Vaught Monoids, and Boolean Algebras.
Regular lattices
Regularity and permutability via transferability of tolerances
Regularity in p-algebras and p-semilattices
Regularity of algebras with applications to congruence class geometry
Relation products of congruences and factor congruences
Relational characterizations of permutable and -permutable varieties
Relational classes and their characterizations
Relations, coverings, hypergraphs and matroids
Relations on the lattice of congruences of a regular semigroup.
Relative Complements in the Weak Congruence Lattice
Remark on partially ordered sets, universal algebras and semigroups
Remarks on tolerance algebras
Representation of undirected graphs by anticommutative conservative groupoids
The paper studies tolerances and congruences on anticommutative conservative groupoids. These groupoids can be assigned in a one-to-one way to undirected graphs.
Residual finiteness of a class of semigroups presented by a single relation.
Residually finite congruences and quasi-regular subsets in uniform algebras