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Semi-perfect and F-semi-perfect modules. (English) Zbl 0581.16019

A module is called semi-perfect iff every factor module has a projective cover. A module is defined to be supplemented iff every submodule has a supplement. F. Kasch and E. A. Mares have shown that M is a semi-perfect module iff M is supplemented [Nagoya Math. J. 27, 525-529 (1966; Zbl 0158.289)]. The author shows that M is semi-perfect if and only if M is supplemented by supplements which have projective covers. The semi-perfectness of M is also equivalent to the statement that M is amply supplemented by supplements with projective covers. Here a module M is defined to the amply supplemented iff \(M=A+B\) implies that A has a supplement in B. The results are also extended to F-semi-perfect, finitely generated modules M. These are finitely generated modules M such that every factor module by a finitely generated submodule has a projective cover [cf. W. Jansen, Commun. Algebra 6, 617-637 (1978; Zbl 0374.16019)].
Reviewer: L.C.A.van Leeuwen

MSC:

16L30 Noncommutative local and semilocal rings, perfect rings
16D40 Free, projective, and flat modules and ideals in associative algebras
16D70 Structure and classification for modules, bimodules and ideals (except as in 16Gxx), direct sum decomposition and cancellation in associative algebras)