The finite presentation of the stable Hom functors, the Bass torsion, and the cotorsion coradical
Abstract
We provide necessary and/or sufficient conditions for the stable Hom functors to be finitely presented. When the covariant Hom functor modulo projectives is finitely presented, its defect is isomorphic to the Bass torsion of the fixed argument. When the contravariant Hom functor modulo injectives is finitely presented, its defect is isomorphic to the cotorsion of the fixed argument. We also give a sufficient condition for the sub-stabilization of the tensor product to be finitely presented. A finite presentation of the tensor product leads to an unexpected application.
- Publication:
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arXiv e-prints
- Pub Date:
- December 2022
- DOI:
- 10.48550/arXiv.2212.09237
- arXiv:
- arXiv:2212.09237
- Bibcode:
- 2022arXiv221209237M
- Keywords:
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- Mathematics - Category Theory;
- Mathematics - Representation Theory;
- 16S90 (Primary 16D90;
- 16E30;
- 18A25 (Secondary)
- E-Print:
- The previous version has been split into two separate papers. Section 4 has been augmented by additional results on linear control systems and made into a separate article entitled "The defect, the Malgrange functor, and linear control systems". The new Section 4 deals with sub-stabilization of the tensor product and with related functors. A new application of the defect has been added