65 research outputs found
On a class of locally Butler groups
summary:A torsionfree abelian group is called a Butler group if for any torsion group . It has been shown in [DHR] that under any countable pure subgroup of a Butler group of cardinality not exceeding is again Butler. The purpose of this note is to show that this property has any Butler group which can be expressed as a smooth union of pure subgroups having countable typesets
Weak Krull-Schmidt theorem
summary:Recently, A. Facchini [3] showed that the classical Krull-Schmidt theorem fails for serial modules of finite Goldie dimension and he proved a weak version of this theorem within this class. In this remark we shall build this theory axiomatically and then we apply the results obtained to a class of some modules that are torsionfree with respect to a given hereditary torsion theory. As a special case we obtain that the weak Krull-Schmidt theorem holds for the class of modules that are both uniform and co-uniform. A simple example shows that this generalizes the result of [3] mentioned above
Precovers
summary:Let be an abstract class (closed under isomorpic copies) of left -modules. In the first part of the paper some sufficient conditions under which is a precover class are given. The next section studies the -precovers which are -covers. In the final part the results obtained are applied to the hereditary torsion theories on the category on left -modules. Especially, several sufficient conditions for the existence of -torsionfree and -torsionfree -injective covers are presented
Relative exact covers
summary:Recently Rim and Teply [11] found a necessary condition for the existence of -torsionfree covers with respect to a given hereditary torsion theory for the category -mod. This condition uses the class of -exact modules; i.e. the -torsionfree modules for which every its -torsionfree homomorphic image is -injective. In this note we shall show that the existence of -torsionfree covers implies the existence of -exact covers, and we shall investigate some sufficient conditions for the converse
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