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The Stacks project

Lemma 13.26.12. Let \mathcal{A} be an abelian category with enough injectives. Let \mathcal{I}^ f \subset \text{Fil}^ f(\mathcal{A}) denote the strictly full additive subcategory whose objects are the filtered injective objects. The canonical functor

K^{+}(\mathcal{I}^ f) \longrightarrow DF^{+}(\mathcal{A})

is exact, fully faithful and essentially surjective, i.e., an equivalence of triangulated categories. Furthermore the diagrams

\xymatrix{ K^{+}(\mathcal{I}^ f) \ar[d]_{\text{gr}^ p} \ar[r] & DF^{+}(\mathcal{A}) \ar[d]_{\text{gr}^ p} \\ K^{+}(\mathcal{I}) \ar[r] & D^{+}(\mathcal{A}) } \quad \xymatrix{ K^{+}(\mathcal{I}^ f) \ar[d]^{\text{forget }F} \ar[r] & DF^{+}(\mathcal{A}) \ar[d]^{\text{forget }F} \\ K^{+}(\mathcal{I}) \ar[r] & D^{+}(\mathcal{A}) }

are commutative, where \mathcal{I} \subset \mathcal{A} is the strictly full additive subcategory whose objects are the injective objects.

Proof. The functor K^{+}(\mathcal{I}^ f) \to DF^{+}(\mathcal{A}) is essentially surjective by Lemma 13.26.9. It is fully faithful by Lemma 13.26.11. It is an exact functor by our definitions regarding distinguished triangles. The commutativity of the squares is immediate. \square


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