English

Hom and Ext, Revisited

Commutative Algebra 2017-11-06 v4

Abstract

Let RR be a commutative Noetherian local ring and M,NM,N be finitely generated RR-modules. We prove a number of results of the form: if \mboxHomR(M,N)\mbox{Hom}_R(M,N) has some nice properties and \mboxExtR1in(M,N)=0\mbox{Ext}^{1 \leq i \leq n}_R(M,N)=0 for some nn, then MM (and sometimes NN) must be be close to free. Our methods are quite elementary, yet they suffice to give a unified treatment, simplify, and sometimes extend a number of results in the literature.

Keywords

Cite

@article{arxiv.1710.05123,
  title  = {Hom and Ext, Revisited},
  author = {Hailong Dao and Mohammad Eghbali and Justin Lyle},
  journal= {arXiv preprint arXiv:1710.05123},
  year   = {2017}
}

Comments

Some typos fixed. Remark 2.1 and Lemma 3.1 were expanded to cover semi-dualizing modules. Remark 3.17 was added

R2 v1 2026-06-22T22:13:25.886Z