A concept of basic matrix semigroups over fields (with some variations) is introduced and throughly investigated. Sections 1 and 2 contain main definitions, Section 3 treats some properties of basic semigroups, Section 4 ...

We completely determine all commutative semigroup varieties that are cancellable elements of the lattice SEM of all semigroup varieties. In particular, we verify that a commutative semigroup variety is a cancellable element ...

A convolution is a mapping C of the set Z + of positive integers into the set P(Z +) of all subsets of Z + such that,for any n ∈ Z +, each member of C(n) is a divisor of n. If D(n) is the set of all divisors of n, for any ...

Modular data are commonly studied in mathe- matics and physics. A modular datum defines a finite-dimensional representation of the modular group SL2(Z). In this paper, we show that there is a one-to-one correspondence ...

In the present work the relations between the closure operators of two module categories are investigated in the case when the given categories are connected by two covariant adjoint functors H : R-Mod −→ S-Mod and T : ...

We construct a simplified resolution for the trivial G-module Z, where G is a finite abelian group, and compare it with the standard resolution. We use it to calculate cohomologies of irreducible G-lattices and their duals.

Let p, q > 2 be relatively prime integers and let Hp,q be the generalized Hecke group associated to p and q. The generalized Hecke group Hp,q is generated by X(z) = −(z − λp)−1 and Y (z) = −(z + λq) −1 where λp = 2 cos ...

It is proved that conjugated periodic elements of the infinite wreath power of a finite permutation group are conjugated in the finite state wreath power of this group. Counterexamples for nonperiodic elements are given.

For a monounary algebra A = (A, f) we study the lattice Quord A of all quasiorders of A, i.e., of all reflexive and transitive relations compatible with f. Monounary algebras (A, f) whose lattices of quasiorders are ...