Let M be a module. A\delta-cover of M is an epimorphism from a module F onto M with
a\delta-small kernel. A\delta-cover is said to be a flat\delta-cover in case F is a flat module. In …

Let be a ring, a class of left-modules, the class of submodules of, and the class of quotient-
modules of. It is shown that is precovering (preenveloping) if and only if every injective …

Let R be a ring. A right R-module M is said to be neat-flat if the kernel of any epimorphism Y-
> M is neat in Y, ie, the induced map Hom (S, Y)-> Hom (S, M) is surjective for any simple …

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 …

868 MARTINEZ HERNANDEZ where F'is a flat and F-divisible module, can be completed
commutatively. b) The diagram can be completed only by means of autornorphisms of F. In …

Let ℰ be an injectively resolving subcategory of left R-modules. We study a particular case of
ℰ-Gorenstein injective and flat modules, called strongly ℰ-Gorenstein injective and flat …

Let R be a ring, na fixed nonnegative integer and F n the class of all left R-modules of flat
dimension at most n. A left R-module M is called n-copure projective if Ext R 1 (M, F)= 0 for …

In this paper modules with ascending chain condition (acc)(respectively, with descending
chain conditon (dcc)) on essential submodules are investigated: Finitely generated quasi …

In this thesis, we conducted a comprehensive study of neat-subgroups of abelian groups. In
this context, we investigated exact sequences, injectivity, projectivity, essential extensions …

In § 1, we begin with a basic theorem which describes a convenient embedding of a
nonsingular left R-module into a complete direct product of copies of the left injective hull of …