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In algebra, Quillen's Q-construction associates to an exact category (e.g., an abelian category) an algebraic K-theory. More precisely, given an exact category ''C'', the construction creates a topological space so that is the Grothendieck group of ''C'' and, when ''C'' is the category of finitely generated projective modules over a ring ''R'', for , is the ''i''-th K-group of ''R'' in the classical sense. (The notation "+" is meant to suggest the construction adds more to the classifying space ''BC''.) One puts : and call it the ''i''-th K-group of ''C''. Similarly, the ''i''-th K-group of ''C'' with coefficients in a group ''G'' is defined as the homotopy group with coefficients: :. The construction is widely applicable and is used to define an algebraic K-theory in a non-classical context. For example, one can define equivariant K-theory as of of the category of equivariant sheaves on a scheme. Waldhausen's S-construction generalizes the Q-construction in a stable sense; in fact, the former, which uses a more general Waldhausen category, produces a spectrum instead of a space. Grayson's binary complex also gives a construction of algebraic K-theory for exact categories.〔Daniel R. Grayson, (Algebraic K-theory via binary complexes )〕 See also module spectrum#K-theory for a K-theory of a ring spectrum. == Operations == Every ring homomorphism induces and thus where is the category of finitely generated projective modules over ''R''. One can easily show this map (called transfer) agrees with one defined in Milnor's ''Introduction to algebraic K-theory''. The construction is also compatible with the suspension of a ring (cf. Grayson). 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「Q-construction」の詳細全文を読む スポンサード リンク
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