Lemma 20.30.6. Let $f : (X, \mathcal{O}_ X) \to (Y, \mathcal{O}_ Y)$ be a morphism of ringed spaces. Let $K$ be in $D(\mathcal{O}_ X)$. Then $H^ i(Rf_*K)$ is the sheaf associated to the presheaf

$V \mapsto H^ i(f^{-1}(V), K) = H^ i(V, Rf_*K)$

Proof. The equality $H^ i(f^{-1}(V), K) = H^ i(V, Rf_*K)$ follows upon taking cohomology from the second statement in Lemma 20.30.5. Then the statement on sheafification follows from Lemma 20.30.3. $\square$

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