Modularity and distributivity of tolerance lattices of commutative inverse semigroups
Modyfications of Csákány's Theorem
Varieties whose algebras have no idempotent element were characterized by B. Csákány by the property that no proper subalgebra of an algebra of such a variety is a congruence class. We simplify this result for permutable varieties and we give a local version of the theorem for varieties with nullary operations.
Non-modular congruence lattices of Rees matrix semigroups
Notes on congruence implication
On congruence distributivity of ordered algebras with constants
We define the order-congruence distributivity at 0 and order- congruence n-distributivity at 0 of ordered algebras with a nullary operation 0. These notions are generalizations of congruence distributivity and congruence n-distributivity. We prove that a class of ordered algebras with a nullary operation 0 closed under taking subalgebras and direct products is order-congruence distributive at 0 iff it is order-congruence n-distributive at 0. We also characterize such classes by a Mal'tsev condition....
On congruence lattices in a category
On finitely based varieties of algebras
On Jónsson's theorem
A proof of Jonsson's theorem inspired by considering a natural topology on algebraic lattices is given.
On modularity in lattices of congruences on ordered sets
On -permutable and distributive at 0 varieties.
On permutability in semigroup varieties
The paper contains characterizations of semigroup varieties whose semigroups with one generator (two generators) are permutable. Here all varieties of regular -semigroups are described in which each semigroup with two generators is permutable.
On schemes for congruence distributivity
We present diagrammatic schemes characterizing congruence 3-permutable and distributive algebras. We show that a congruence 3-permutable algebra is congruence meetsemidistributive if and only if it is distributive. We characterize varieties of algebras satisfying the so-called triangular scheme by means of a Maltsev-type condition.
On the congruence extension property.
On the ring of the variety of algebras over a ring
On the structure of equationally complete varieties. I
Orthorings
Certain ring-like structures, so-called orthorings, are introduced which are in a natural one-to-one correspondence with lattices with 0 every principal ideal of which is an ortholattice. This correspondence generalizes the well-known bijection between Boolean rings and Boolean algebras. It turns out that orthorings have nice congruence and ideal properties.
Permutability of distributive congruence relations in a joint semilattice directed below
Präprimale Algebren, die arithmetische Varietäten erzeugen
Prime ideals in universal algebras
Properties of relatively pseudocomplemented directoids
The concept of a relatively pseudocomplemented directoid was introduced recently by the first author. It was shown that the class of relatively pseudocomplemented directoids forms a variety whose axiom system contains seven identities. The aim of this paper is three-fold. First we show that these identities are not independent and their independent subset is presented. Second, we modify the adjointness property known for relatively pseudocomplemented semilattices in the way which is suitable for...