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Compact modules over nonsingular rings
Kálnai, Peter ; Žemlička, Jan (advisor) ; Breaz, Simion (referee) ; Příhoda, Pavel (referee)
This doctoral thesis provides several new results in which we leverage the inner structure of non-singular rings, in particular of self-injective von Neumann regular rings. First, we describe categorical and set-theoretical conditions under which all products of compact objects remain compact, where the notion of compactness is relativized with respect to a fixed subclass of objects. A special instance when such closure property holds are the classic module categories over rings of our interest. Moreover, we show that a potential counterexample for Köthe's Conjecture might be in the form of a countable local subring of a suitable simple self-injective von Neumann regular ring. 1
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Testing the projectivity of modules
Matoušek, Cyril ; Šaroch, Jan (advisor) ; Žemlička, Jan (referee)
In this thesis, we study the problem of the existence of test modules for the projectivity. A right R-module is said to be a test module if it holds for every right R-module M that M is projective whenever T ∈ M⊥ . We show that test modules exist over right perfect rings, although their existence is not provable in ZFC in case of non-right perfect rings. In order to prove this, we use Shelah's uni- formization principle, which is independent of the axioms of ZFC. Furthermore, we show that test modules exist over rings of finite global dimension assuming the weak diamond principle, which is also independent of ZFC. 1
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Kompaktní objekty v kategoriích modulů
Kálnai, Peter ; Žemlička, Jan (advisor) ; Příhoda, Pavel (referee)
Title: Compact objects in categories of modules Author: Peter Kálnai Department: Department of Algebra Supervisor: Mgr. Jan Žemlička, Ph.D., Department of Algebra Abstract: In the thesis we state baic properties of compact objects in various appropriate categories like categories of modules, stable factor category over a perfect ring and Grothendieck categories. We find a ring R such that the class of dually slender R-modules is closed under direct products under some set-theoretic assumption. Finally, we characterize the conditions, when countably generat- ed projective modules are finitely generated, expressed by their Grothendieck monoid. Keywords: compact, dually slender module, stable module category, projective module, self-small
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