- (1) There is an error in the proof of Theorem 7.12 (GM Duality) of . The statement itself is correct, and it is repeated as Theorem 9 below, with a correct proof.(2) Just before formula (3.12) in , we said that “Moda-tor A is a thick abelian subcategory of Mod A”. This is true if the ideal a is finitely generated, but might be false otherwise. There is no implication of this error on the rest of the paper, since WPR ideals are by definition finitely generated. We thank R. Vyas for mentioning this error to us.