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Groupoid scheme : ウィキペディア英語版 | Groupoid scheme In algebraic geometry, a groupoid scheme is a pair of schemes together with five morphisms satisfying are the identity morphisms, and other obvious conditions that generalize the axioms of group action; e.g., associativity. In practice, it is usually written as (cf. coequalizer.) Example: Suppose an algebraic group ''G'' acts from the right on a scheme ''U''. Then take , ''s'' the projection, ''t'' the given action. The main use of the notion is that it provides an atlas for a stack. More specifically, let be the category of -torsors. Then it is a category fibered in groupoids; in fact, a Deligne–Mumford stack. Conversely, any DM stack is of this form. == Notes ==
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「Groupoid scheme」の詳細全文を読む
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