9 research outputs found
Torsion-free, divisible, and Mittag-Leffler modules
We study (relative) K-Mittag-Leffler modules, with emphasis on the class K of
absolutely pure modules. A final goal is to describe the K-Mittag-Leffler
abelian groups as those that are, modulo their torsion part, aleph_1-free,
Cor.6.12. Several more general results of independent interest are derived on
the way. In particular, every flat K-Mittag-Leffler module (for K as before) is
Mittag-Leffler, Thm.3.9. A question about the definable subcategories generated
by the divisible modules and the torsion-free modules, resp., has been left
open, Quest.4.6
Modules as exact functors
We can define a module to be an exact functor on a small abelian category.
This is explained and shown to be equivalent to the usual definition but it
does offer a different perspective, inspired by the notions from model theory
of imaginary sort and interpretation. A number of examples are worked through
Some model theory over hereditary noetherian domains
Questions in the model theory of modules over hereditary noetherian domains are investigated with particular attention being paid to differential polynomial rings and to generalized Weyl algebras. We prove that there exists no isolated point in the Ziegler spectrum over a simple hereditary generalized Weyl algebra A of the sort considered by Bavula [Algebra i Analiz 4(1) (1992), 75β97] over a field k with char(k) = 0 (the first Weyl algebra A1(k) is one such) and the category of finite length modules over A does not have any almost split sequence. We show that the theory of all modules over a wide class of generalized Weyl algebras and related rings interprets the word problem for groups, and in the case that the field is countable there exists a superdecomposable pure-injective module over A. This class includes, for example, the universal enveloping algebra Usl2(k)
Model theory in compactly generated (tensor-)triangulated categories
We give an account of model theory in the context of compactly generated
triangulated and tensor-triangulated categories . We describe pp
formulas, pp-types and free realisations in such categories and we prove
elimination of quantifiers and elimination of imaginaries. We compare the ways
in which definable subcategories of may be specified. Then we link
definable subcategories of and finite-type torsion theories on the
category of modules over the compact objects of . We briefly consider
spectra and dualities. If is tensor-triangulated then new features
appear, in particular there is an internal duality in rigidly-compactly
generated tensor-triangulated categories