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In the branches of abstract algebra known as ring theory and module theory, each right (resp. left) ''R'' module ''M'' has a singular submodule consisting of elements whose annihilators are essential right (resp. left) ideals in ''R''. In set notation it is usually denoted as . For general rings, is a good generalization of the torsion submodule tors(''M'') which is most often defined for domains. In the case that ''R'' is a commutative domain, . If ''R'' is any ring, is defined considering ''R'' as a right module, and in this case is a twosided ideal of ''R'' called the right singular ideal of ''R''. Similarly the left handed analogue is defined. It is possible for . ==Definitions== Here are several definitions used when studying singular submodule and singular ideals. In the following, ''M'' is an ''R'' module: *''M'' is called a singular module if . *''M'' is called a nonsingular module if . *''R'' is called right nonsingular if . A left nonsingular ring is defined similarly, using the left singular ideal, and it is entirely possible for a ring to be right-but-not-left nonsingular. In rings with unity it is always the case that , and so "right singular ring" is not usually defined the same way as singular modules are. Some authors have used "singular ring" to mean "has a nonzero singular ideal", however this usage is not consistent with the usage of the adjectives for modules. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Singular submodule」の詳細全文を読む スポンサード リンク
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