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Faithfully Exact Functors and Their Applications to Projective Modules and Injective Modules

Published online by Cambridge University Press:  22 January 2016

Takeshi Ishikawa
Takeshi Ishikawa*
Affiliation:
Tokyo Metropolitan University
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The aim of this paper is to study a property of a special kind of exact functors and give some applications to projective modules and injective modules.

In section 1 we introduce the notion of faithfully exact functors [Definition 1] as a generalization of the functor T(X) = X⊗M, where M is a faithfully flat module, and give a property of this class of functors [Theorem 1.1]. Next, applying this general theory to functors ⊗ and Horn, we define the notion of faithfully projective modules [Definition 2] and faithfully injective modules [Definition 3]. In the commutative case “faithfully projective” means, however, simply “projective and faithfully flat” [Proposition 2.3]. In section 2, equivalent conditions for a projective module P to be faithfully projective are given [Theorem 2.2, Proposition 2. 3 and 2.4]. And a simpler proof is given to Y. Hinohara’s result [6] asserting that projective modules over an indecomposable weakly noetherian ring are faithfully flat [Proposition 2.5]. In section 3, we consider faithfully injective modules.

Type
Research Article
Information
Nagoya Mathematical Journal , Volume 24 , June 1964 , pp. 29 - 42
Copyright
Copyright © Editorial Board of Nagoya Mathematical Journal 1964

References

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