
If R is a locally bounded K-category, K some algebraically closed field, G a group of K-linear automorphisms of R acting freely on the objects of R, then it was proved by \textit{P. Gabriel} [in: Representations of algebras, Lect. Notes Math. 903, 68-105 (1981; Zbl 0481.16008), \textit{K. Bongartz}, \textit{P. Gabriel}, Invent. Math. 65, 331-378 (1982; Zbl 0482.16026), \textit{R. Martínez-Villa}, \textit{J. A. de la Peña}, Invent. Math. 72, 359-362 (1983; Zbl 0491.16028)] for example that R is locally representation finite if and only if so is R/G. Moreover the push down functor \(F_{\lambda}: mod R\to mod (R/G)\) induces a bijection between G-orbits of indecomposable R-modules and indecomposable R/G- modules. If R is not locally representation finite in general the functor \(F_{\lambda}\) is not surjective on object classes. The authors successfully investigate the full subcateogry \(mod_ 2(R/G)\) of mod (R/G) defined by those modules having no direct summand isomorphic to \(F_{\lambda}(M)\) for some \(M\in mod R.\) As a first result they state in (2.3): \(X\in mod_ 2(R/G)\) iff there exists a decomposition \(F.(X)=\oplus Y_ i\) (F. the pull up functor) where all \(Y_ i\) are weakly-G-periodic. (Y is called weakly periodic if the support supp Y of Y is infinite and \((supp\;Y)/G_ Y\) is finite, \(G_ Y\) the stabilizer of Y.) Main result of the paper is the following Theorem: Let R be a locally bounded K-category and G a group of automorphisms of R which acts freely on \((ind\;R)/\cong\). Let \({\mathfrak S}\) be a separating family of subcategories of R with respect to G and \({\mathfrak S}_ 0\) a fixed set of representatives of G-orbits of \({\mathfrak S}\). Then there exists an equivalence of categories \[ E:\coprod_{L\in {\mathfrak S}_ 0}(mod L/G_ L)/[mod_ 1L/G_ L]\to (mod R/G)/[mod_ 1R/G]. \] As a consequence, the Auslander-Reiten quiver \(\Gamma_{R/G}\) of R/G is isomorphic to the disjoint union of translation-quivers \(\Gamma_ R/G\coprod (\coprod_{L\in {\mathfrak S}_ 0}(\Gamma_{L/G_ L})_ 2)\), where \((\Gamma_{L/G_ L})_ 2\) is the union of connected components of \(\Gamma_{L/G_ l}\) whose points are \(L/G_ L\)-modules of second kind. (For the definition of a separating family of subcategories see (3.1) of the paper.) In {\S} 4 the authors show that each indecomposable locally finite dimensional R-module X is a limit of a sequence of finite dimensional (indecomposable) modules \((Y_ n)\), the fundamental R- sequence produced by S. {\S} 5 finally is devoted to carefully chosen examples and applications.
Category-theoretic methods and results in associative algebras (except as in 16D90), separating family, locally bounded K-category, pull up functor, equivalence of categories, push down functor, Representation theory of associative rings and algebras, Other classes of modules and ideals in associative algebras, Article, group of automorphisms, indecomposable locally finite dimensional R-module, Auslander- Reiten quiver, 510.mathematics, translation-quivers, connected components, Module categories in associative algebras, Finite rings and finite-dimensional associative algebras, locally representation finite, indecomposable R-modules
Category-theoretic methods and results in associative algebras (except as in 16D90), separating family, locally bounded K-category, pull up functor, equivalence of categories, push down functor, Representation theory of associative rings and algebras, Other classes of modules and ideals in associative algebras, Article, group of automorphisms, indecomposable locally finite dimensional R-module, Auslander- Reiten quiver, 510.mathematics, translation-quivers, connected components, Module categories in associative algebras, Finite rings and finite-dimensional associative algebras, locally representation finite, indecomposable R-modules
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