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Projective cover : ウィキペディア英語版 | Projective cover In the branch of abstract mathematics called category theory, a projective cover of an object ''X'' is in a sense the best approximation of ''X'' by a projective object ''P''. Projective covers are the dual of injective envelopes. == Definition ==
Let be a category and ''X'' an object in . A projective cover is a pair (''P'',''p''), with ''P'' a projective object in and ''p'' a superfluous epimorphism in Hom(''P'', ''X''). If ''R'' is a ring, then in the category of ''R''-modules, a superfluous epimorphism is then an epimorphism such that the kernel of ''p'' is a superfluous submodule of ''P''.
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「Projective cover」の詳細全文を読む
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