Generalized Hill lemma, Kaplansky theorem for cotorsion pairs and some applications

J Šťovíček, J Trlifaj - The Rocky Mountain Journal of Mathematics, 2009 - JSTOR
We generalize Hill's lemma in order to obtain a large family of C-filtered submodules from a
single C-filtration of a module. We use this to prove the following generalization of …

[引用][C] The torsion submodule splits off

ML Teply, JD Fuelberth - Mathematische Annalen, 1970 - Springer
A classical question for modules over an integral domain is," When is the torsion submodule
t (A) of a module A a direct summand of AT'A module is said to split when its torsion …

Local splitters for bounded cotorsion theories

J Trlifaj - 2002 - degruyter.com
Let CA, B be a bounded cotorsion theory and K be a local splitter for C. We prove that
Shelah's uniformization principle UP implies that C is not generated by K. As corollaries, we …

Pure injectivity of n-cotilting modules: the Prüfer and the countable case

S Bazzoni, R Göbel, L Strüngmann - Archiv der Mathematik, 2005 - Springer
We will prove that if a ring R is either countable or a Prüfer domain, then n-cotilting R-
modules are pure injective. We can apply and modify a very nice argument due to Jensen …

Cotilting modules are pure-injective

S Bazzoni - Proceedings of the American Mathematical Society, 2003 - JSTOR
Cotilting Modules Are Pure-Injective Page 1 PROCEEDINGS OF THE AMERICAN
MATHEMATICAL SOCIETY Volume 131, Number 12, Pages 3665-3672 S 0002-9939(03)06938-7 …

Direct limits of modules of finite projective dimension

LA Hügel, J Trlifaj - Rings, Modules, Algebras, and Abelian …, 2004 - books.google.com
We describe in homological terms the direct limit closure of a class C of modules over a ring
R. We also determine the closure of the cotorsion pair=(A, B) cogenerated by C. As an …

Approximations and Mittag-Leffler conditions the applications

L Angeleri Hügel, J Śaroch, J Trlifaj - Israel Journal of Mathematics, 2018 - Springer
A classic result by Bass says that the class of all projective modules is covering if and only if
it is closed under direct limits. Enochs extended the if-part by showing that every class of …

A new version of a theorem of Kaplansky

F Wang, L Qiao - Communications in Algebra, 2020 - Taylor & Francis
A well-known theorem of Kaplansky states that any projective module is a direct sum of
countably generated modules. In this paper, we prove the w-version of this theorem, where …

Covers, precovers, and purity

H Holm, P Jørgensen - Illinois Journal of Mathematics, 2008 - projecteuclid.org
We show that if a class of modules is closed under pure quotients, then it is precovering if
and only if it is covering, and this happens if and only if it is closed under direct sums. This is …

Cotorsion theories and splitters

R Göbel, S Shelah - Transactions of the American Mathematical Society, 2000 - ams.org
Let $ R $ be a subring of the rationals. We want to investigate self splitting $ R $-modules $
G $(that is $\operatorname {Ext} _R (G, G)= 0) $. Following Schultz, we call such modules …