English

Contramodules over pro-perfect topological rings

Category Theory 2022-01-12 v6 Rings and Algebras

Abstract

For four wide classes of topological rings R\mathfrak R, we show that all flat left R\mathfrak R-contramodules have projective covers if and only if all flat left R\mathfrak R-contramodules are projective if and only if all left R\mathfrak R-contramodules have projective covers if and only if all descending chains of cyclic discrete right R\mathfrak R-modules terminate if and only if all the discrete quotient rings of R\mathfrak R are left perfect. Three classes of topological rings for which this holds are the complete, separated topological associative rings with a base of neighborhoods of zero formed by open two-sided ideals such that either the ring is commutative, or it has a countable base of neighborhoods of zero, or it has only a finite number of semisimple discrete quotient rings. The fourth class consists of all the topological rings with a base of neighborhoods of zero formed by open right ideals which have a closed two-sided ideal with certain properties such that the quotient ring is a topological product of rings from the previous three classes. The key technique on which the proofs are based is the contramodule Nakayama lemma for topologically T-nilpotent ideals.

Keywords

Cite

@article{arxiv.1807.10671,
  title  = {Contramodules over pro-perfect topological rings},
  author = {Leonid Positselski},
  journal= {arXiv preprint arXiv:1807.10671},
  year   = {2022}
}

Comments

LaTeX 2e with xy-pic, 53 pages, 3 commutative diagrams; v2: this is an improved version of Sections 1-10 of v1, the rest of v1 was moved to arXiv:1907.04973 and arXiv:1907.05537; v.5: Sections 1.8, 1.9, 1.10, and 1.11 expanded; v.6: small additions and corrections, references updated, the numbering of sections (and of subsections in the introduction) shifted to agree with the journal version

R2 v1 2026-06-23T03:17:11.263Z