Algebra, as we know it today, consists of many different ideas, concepts and results. A rea-
sonable estimate of the number of these different “items” would be somewhere between …

This volume offers a systematic, comprehensive investigation of field extensions, finite or
not, that possess a Cogalois correspondence. The subject is somewhat dual to the very …

In this paper we extend the concept of the group of covering automorphisms associated to a
universal covering space ϕ: U→ X (where X is a connected topological manifold), to the …

We prove that for certain classes of modules $\mathcal {F} $ such that direct sums of
$\mathcal {F} $-covers ($\mathcal {F} $-envelopes) are $\mathcal {F} $-covers ($\mathcal {F} …

We describe the structure of finitely generated cotorsion modules over commutative
noetherian rings. Also we characterize the so-called covering morphisms between finitely …

This paper is motivated by S. Park [10] in which the injective cover of left R [x]-module M [x-1]
of inverse polynomials over a left R-module M was discussed. The author considers the Ω …

Czechoslovak Mathematical Journal Page 1 Czechoslovak Mathematical Journal Edgar E.
Enochs; Juan Rada Abelian groups which have trivial absolute coGalois group …

Given a ring R and a torsion theory on the category of left R-modules, the map Ψ: C→ M is a
torsion free precover of the R-module M if C is a torsion free R-module and every map from F …

Let ℒ be a class of right modules, whenever covers and envelopes exist, we show that if ℒ is
closed under extensions and direct summands, then P (ℒ), the class of all ℒ-projective right …

We investigate purity and approximation with respect to a class of morphisms of modules.
Let ℐ be a class of left R-module morphisms. An epimorphism ϕ: A→ B of left R-modules is …