On Ext and Hyperext groups in the category of functors

Let R be a commutative noetherian ring with unit and let f denote the category of functors from the category of finitely generated R-modules to R-modules. Let I in f denote the inclusion functor. We study homological algebra of I in the category f (Ext-groups) and its generalization when we allow coefficients to be chain complexes in f (Hyperext-groups). We compare the Ext-groups of I with coefficients in arbitrary F in f with Ext-groups of I with coefficients in stable derived functors of F. The latter groups are relatively easily calculable because the stable derived functors are linear. On the other hand, known calculations of Ext-groups of I with coefficients in F can shed light on the stable derived functors of F which are hard to approach.

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Publication Details

Journal
Gulf Journal of Mathematics
Published
2025-08-18
DOI
https://doi.org/10.56947/gjom.v20i2.3211
Primary Topic
Homotopy and Cohomology in Algebraic Topology
Type
article
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article

On Ext and Hyperext groups in the category of functors

Stanisław Betley
Gulf Journal of Mathematics
Homotopy and Cohomology in Algebraic Topology
article

On Ext and Hyperext groups in the category of functors

Stanisław Betley
article en

Abstract

Let R be a commutative noetherian ring with unit and let f denote the category of functors from the category of finitely generated R-modules to R-modules. Let I in f denote the inclusion functor. We study homological algebra of I in the category f (Ext-groups) and its generalization when we allow coefficients to be chain complexes in f (Hyperext-groups). We compare the Ext-groups of I with coefficients in arbitrary F in f with Ext-groups of I with coefficients in stable derived functors of F. The latter groups are relatively easily calculable because the stable derived functors are linear. On the other hand, known calculations of Ext-groups of I with coefficients in F can shed light on the stable derived functors of F which are hard to approach.

Gulf Journal of MathematicsVol. 20(2)
Institute of Mathematics (PL), University of Warsaw (PL)
Openalex Percentile: Top 73%
Homotopy and Cohomology in Algebraic Topology
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