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Hereditary ring : ウィキペディア英語版 | Hereditary ring In mathematics, especially in the area of abstract algebra known as module theory, a ring ''R'' is called hereditary if all submodules of projective modules over ''R'' are again projective. If this is required only for finitely generated submodules, it is called semihereditary. For a noncommutative ring ''R'', the terms left hereditary and left semihereditary and their right hand versions are used to distinguish the property on a single side of the ring. To be left (semi-)hereditary, all (finitely generated) submodules of projective ''left'' ''R''-modules must be projective, and to be right (semi-)hereditary all (finitely generated) submodules of projective right submodules must be projective. It is possible for a ring to be left (semi-)hereditary but not right (semi-)hereditary, and vice versa. ==Equivalent definitions==
* The ring ''R'' is left (semi-)hereditary if and only if all (finitely generated) left ideals of ''R'' are projective modules. * The ring ''R'' is left hereditary if and only if all left modules have projective resolutions of length at most 1. Hence the usual derived functors such as and are trivial for .
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「Hereditary ring」の詳細全文を読む
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