Projective Covers of Flat Contramodules

Author:

Bazzoni Silvana1,Positselski Leonid2,Šťovíček Jan3

Affiliation:

1. Dipartimento di Matematica “Tullio Levi-Civita”, Università di Padova, Via Trieste 63, 35121 Padova, Italy

2. Institute of Mathematics of the Czech Academy of Sciences, Žitná 25, 115 67 Prague 1, Czech Republic, and Laboratory of Algebra and Number Theory, Institute for Information Transmission Problems, Moscow 127051, Russia

3. Faculty of Mathematics and Physics, Department of Algebra, Charles University in Prague, Sokolovská 83, 186 75 Praha, Czech Republic

Abstract

Abstract We show that a direct limit of projective contramodules (over a right linear topological ring) is projective if it has a projective cover. A similar result is obtained for $\infty $-strictly flat contramodules of projective dimension not exceeding $1$, using an argument based on the notion of the topological Jacobson radical. Covers and precovers of direct limits of more general classes of objects, both in abelian categories with exact and with nonexact direct limits, are also discussed, with an eye towards the Enochs conjecture about covers and direct limits, using locally split (mono)morphisms as the main technique. In particular, we offer a simple elementary proof of the Enochs conjecture for the left class of an $n$-tilting cotorsion pair in an abelian category with exact direct limits.

Funder

MIUR-PRIN

Padova University

Czech Science Foundation

Publisher

Oxford University Press (OUP)

Subject

General Mathematics

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