ABSTRACT
The question is answered in terms of flat covers, flat cotorsion modules, and cotorsion envelopes. It is shown that the corresponding class of rings properly contains that of coherent rings. The perfect rings among those are given a ring-theoretic description.
ACKNOWLEDGMENTS
I am grateful to Ed Enochs, Ivo Herzog, and the referee for valuable comments.
Notes
1Note the related result contained in Citation[5].
*For an independent treatment see Auslander M.; Smalo, S. O. Preprojective Modules over Artin Algebras, J. Algebra 1980, 66, 61–122.