arXiv subjects

Josef Dvořák

Publications and source records attributed to Josef Dvořák.

4 recordsLinked to original sources

arXiv2022

Connected objects in categories of $S$-acts

In this paper, the categorial property of compactness of an object, i. e. commuting of the corresponding $\Hom$ functor with coproducts, is studied in categories of $S$-acts and the corresponding structural properties of compact $S$-acts are shown. In order to establish a general context and to unify the approach to both of the most important categories of $S$-acts, the notion of a concrete category with unique decomposition of objects is introduced and studied.

math.CT↗

arXiv2021

Perfect monoids with zero and categories of $S$-acts

In this paper, we study the relationship between the two main categories of $S$-acts for a monoid $S$ with zero from the viewpoint of existence of projective covers and the equivalence is proven. Furthermore, monoids with zeros over which all compact acts are cyclic are characterized.

math.GR↗

arXiv2021

Self-small products of abelian groups

For abelian groups $A, B$, $A$ is called $B$-small if the covariant functor $Hom(A,-)$ commutes with all direct sums $B^{(κ)}$ and $A$ is self-small provided it is $A$-small. The paper characterizes self-small products applying developed closure properties of the classes of relatively small groups. As a consequence, self-small products of finitely generated abelian groups are described.

math.GR↗

arXiv2021

Autocompact objects of Ab5 categories

The aim of the paper is to describe autocompact objects in Ab5-categories, i.e. objects in cocomplete abelian categories with exactness preserving filtered colimits of exact sequences, whose covariant Hom-functor commutes with copowers of the object itself. A characterization of non-autocompact object is given, a general criterion of autocompactness of an object via the structure of its endomorphism ring is presented and a criterion of autocompactness of products is proven.

math.CT↗