We prove the following results for a ring R.(a) If C is a class of right R-modules closed under
direct summands and isomorphisms, then every right R-module has an epic C-envelope if …

Let I be a left or right ideal of the category of left R-modules. We first study the closure
properties of I-preenvelopes and I-precovers of modules under direct sums, direct products …

A well known problem in the theory of envelopes is to characterize those rings having the
property that every (finitely generated, finitely presented, simple) module has a projective …

Throughout this paper, T is a ring with identity and F is a unitary left module over T. This
paper study the relation between semihollow-lifting modules and semiprojective covers …

The purpose of this dissertation is to study weakly projective modules, a concept dual to that
of weakly injective modules. Let M and N be right R-modules. M is called weakly N …

In the present paper, modules which are subisomorphic (in the sense of Goldie) to their pure-
injective envelopes are studied. These modules will be called almost pure-injective …

It is well known that over a left Notherian ring any direct sum of injecive modules is again
injective, and every injective module is a direct sum of indecomposable modules. Faith [6] …

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 …

Let R be a ring and na fixed non-negative integer. C and D denote the classes of all left R-
modules with pure-injective dimension and pure-projective dimension at most n …