On clones determined by their initial segments
On congruences in direct sums of algebras
On direct limit classes of algebras
On the structure of semilattice sums
Presolid varieties of n-semigroups
he class of all M-solid varieties of a given type t forms a complete sublattice of the lattice ℒ(τ) of all varieties of algebrasof type t. This gives a tool for a better description of the lattice ℒ(τ) by characterization of complete sublattices. In particular, this was done for varieties of semigroups by L. Polák ([10]) as well as by Denecke and Koppitz ([4], [5]). Denecke and Hounnon characterized M-solid varieties of semirings ([3]) and M-solid varieties of groups were characterized by Koppitz...
Products of multialgebras and their fundamental algebras.
Refinement Monoids, Vaught Monoids, and Boolean Algebras.
Reg-strongly solid varieties of commutative semigroups
Relation products of congruences and factor congruences
Remarks on tolerance algebras
Retract varieties of monounary algebras
Strict refinement for direct sums and graphs.
Strong amalgamations of lattice ordered groups and modules.
Sturdy frames of type (2,2) algebras and their applications to semirings
We introduce sturdy frames of type (2,2) algebras, which are a common generalization of sturdy semilattices of semigroups and of distributive lattices of rings in the theory of semirings. By using sturdy frames, we are able to characterize some semirings. In particular, some results on semirings recently obtained by Bandelt, Petrich and Ghosh can be extended and generalized.
The groupoid of 0-reduced varieties of Semigroups (n).
The semantical hyperunification problem
A hypersubstitution of a fixed type τ maps n-ary operation symbols of the type to n-ary terms of the type. Such a mapping induces a unique mapping defined on the set of all terms of type t. The kernel of this induced mapping is called the kernel of the hypersubstitution, and it is a fully invariant congruence relation on the (absolutely free) term algebra of the considered type ([2]). If V is a variety of type τ, we consider the composition of the natural homomorphism with the mapping induced...
The strong amalgamation property and (effective) codescent morphisms.
Tree transformations defined by hypersubstitutions
Tree transducers are systems which transform trees into trees just as automata transform strings into strings. They produce transformations, i.e. sets consisting of pairs of trees where the first components are trees belonging to a first language and the second components belong to a second language. In this paper we consider hypersubstitutions, i.e. mappings which map operation symbols of the first language into terms of the second one and tree transformations defined by such hypersubstitutions....
Über die Vollständigkeit der induktiven Gruppoide der partiellen Automorphismen von Algebren
Varieties of algebras with equationally definable zeros