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K-theory and Noncommutative Geometry.pdf

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400 G. Garkusha and M. Prest(A thick subcategory is a triangulated subcategory closed under direct summands).Given a perfect complex X 2 D per .R/ denote by supp.X/ DfP 2 Spec R jX ˝LR R P ¤ 0g. It is easy to see thatsupp.X/ D [ n2Zsupp R .H n .X//;where H n .X/ is the nth homology group of X.Theorem 4.1 (Thomason [18]). Let R be a commutative ring. The assignmentsT 2 L thick .D per .R// 7! [supp.X/andX2TV 2 L.Spec R/ 7! fX 2 D per .R/ j supp.X/ V gare mutually inverse lattice isomorphisms.Given a subcategory X in Mod R, we may consider the smallest torsion class offinite type in Mod R containing X. This torsion class we denote byp \X D fS Mod R j S X is a torsion class of finite typeg:Theorem 4.2. (cf. Garkusha–Prest [8, Theorem C]) Let R be a commutative ring.There are bijections between• the set of all open subsets Y .Inj fg R/ ,• the set of all torsion classes of finite type in Mod R,• the set of all thick subcategories of D per .R/.These bijections are defined as follows:´S D¹M j .M / Y º;Y 7!T D¹X 2 D per .R/ j .H n .X// Y for all n 2 ZºI8ˆ< Y D [ /;S 7! M 2S.Mˆ:T D¹X 2 D per .R/ j H n .X/ 2 S for all n 2 ZºI8ˆ< Y D [.H n .X//;T 7! X2T ;n2Zˆ:S D p ¹H n .X/ j X 2 T ;n2 Zº:

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