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RISS 인기검색어
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- 저자 : Yilmaz Durugun (검색결과 2 건)
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Yilmaz Durugun,Salahattin Ozdemir 대한수학회 2017 대한수학회지 Vol.54 No.4
A submodule $N$ of a module $M$ is called $\mathcal{S}$-closed (in $M$) if $M/N$ is nonsingular. It is well-known that the class $\closed$ of short exact sequences determined by closed submodules is a proper class in the sense of Buchsbaum. However, the class $\mathcal{S}-\closed$ of short exact sequences determined by $\mathcal{S}$-closed submodules need not be a proper class. In the first part of the paper, we describe the smallest proper class $\langle\mathcal{S}-\closed\rangle$ containing $\mathcal{S}-\closed$ in terms of $\mathcal{S}$-closed submodules. We show that this class coincides with the proper classes projectively generated by Goldie torsion modules and coprojectively generated by nonsingular modules. Moreover, for a right nonsingular ring $R$, it coincides with the proper class generated by neat submodules if and only if $R$ is a right SI-ring. In abelian groups, the elements of this class are exactly torsion-splitting. In the second part, coprojective modules of this class which we call \emph{ec-flat} modules are also investigated. We prove that injective modules are ec-flat if and only if each injective hull of a Goldie torsion module is projective if and only if every Goldie torsion module embeds in a projective module. For a left Noetherian right nonsingular ring $R$ of which the identity element is a sum of orthogonal primitive idempotents, we prove that the class $\langle\mathcal{S}-\closed\rangle $ coincides with the class of pure-exact sequences of modules if and only if $R$ is a two-sided hereditary, two-sided $CS$-ring and every singular right module is a direct sum of finitely presented modules.
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CONEAT SUBMODULES AND CONEAT-FLAT MODULES
Engin Buyukasik,Yilmaz Durugun 대한수학회 2014 대한수학회지 Vol.51 No.6
A submodule N of a right R-module M is called coneat if for every simple right R-module S, any homomorphism N → S can be extended to a homomorphism M → S. M is called coneat-flat if the kernel of any epimorphism Y → M → 0 is coneat in Y . It is proven that (1) coneat submodules of any right R-module are coclosed if and only if R is right K-ring; (2) every right R-module is coneat-flat if and only if R is right V -ring; (3) coneat submodules of right injective modules are exactly the modules which have no maximal submodules if and only if R is right small ring. If R is commutative, then a module M is coneat- flat if and only if M + is m-injective. Every maximal left ideal of R is finitely generated if and only if every absolutely pure left R-module is m- injective. A commutative ring R is perfect if and only if every coneat-flat module is projective. We also study the rings over which coneat-flat and flat modules coincide.
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