Precovering and preenveloping ideals

Abstract

L. Salce introduced the notion of a cotorsion pair (F,C) in the category of abelian groups. But his definitions and basic results carry over to more general abelian categories and have proven useful in a variety of settings. A significant result of cotorsion theory proven by Eklof and Trlifaj is that if a pair (F,C) of classes of R-modules is cogenerated by a set, then it is complete. Recently Herzog, Fu, Asensio and Torrecillas developed the ideal approximation theory. In this article we look at a result motivated by the Eklof-Trlifaj argument for an ideal I when it is generated by a set of homomorphisms.