On tolerance relations
On traces of maximal clones.
On transitive operations in abstract algebras
On t-semigroups.
On two classes of hereditarily finitely based semigroup identities.
On universal algebras having bases of different cardinalities
On universality of semigroup varieties
A category is called -determined if every set of non-isomorphic -objects such that their endomorphism monoids are isomorphic has a cardinality less than . A quasivariety is called -universal if the lattice of all subquasivarieties of any quasivariety of finite type is a homomorphic image of a sublattice of the lattice of all subquasivarieties of . We say that a variety is var-relatively alg-universal if there exists a proper subvariety of such that homomorphisms of whose image does...
On varieties generated by Boolean clones.
On varieties of clones.
On varieties of combinatorial inverse semigroups I.
On varieties of combinatorial inverse semigroups II.
On varieties of completely regular semigroups.
On varieties of completely regular semigroups II.
On varieties of completely regular semigroups III.
On varieties of graphs
In this paper, we introduce the notion of a variety of graphs closed under isomorphic images, subgraph identifications and induced subgraphs (induced connected subgraphs) firstly and next closed under isomorphic images, subgraph identifications, circuits and cliques. The structure of the corresponding lattices is investigated.
On varieties of left distributive left idempotent groupoids
We describe a part of the lattice of subvarieties of left distributive left idempotent groupoids (i.e. those satisfying the identities x(yz) ≈ (xy)(xz) and (xx)y ≈ xy) modulo the lattice of subvarieties of left distributive idempotent groupoids. A free groupoid in a subvariety of LDLI groupoids satisfying an identity xⁿ ≈ x decomposes as the direct product of its largest idempotent factor and a cycle. Some properties of subdirectly ireducible LDLI groupoids are found.
On Varieties of Literally Idempotent Languages
A language L ⊆A* is literally idempotent in case that ua2v ∈ L if and only if uav ∈ L, for each u,v ∈ A*, a ∈ A. Varieties of literally idempotent languages result naturally by taking all literally idempotent languages in a classical (positive) variety or by considering a certain closure operator on classes of languages. We initiate the systematic study of such varieties. Various classes of literally idempotent languages can be characterized using syntactic methods. A starting example is the...
On varieties of non-indexed algebras
On varieties of orgraphs
In this paper we investigate varieties of orgraphs (that is, oriented graphs) as classes of orgraphs closed under isomorphic images, suborgraph identifications and induced suborgraphs, and we study the lattice of varieties of tournament-free orgraphs.
On varieties of pseudo -algebras
In this paper we investigate the relation between the lattice of varieties of pseudo -algebras and the lattice of varieties of lattice ordered groups.