Bass characterized the rings R with the property that every left R-module has a projective cover. These are the left perfect rings. A ring is left perfect if and only if the class of projective ...

Jacob R. Matijevic, Maximal Ideal Transforms of Noetherian Rings, Proceedings of the American Mathematical Society, Vol. 54, No. 1 (Jan., 1976), pp. 49-52 ...