Lemma 21.33.8. Let $(\mathcal{C}, \mathcal{O})$ be a ringed site. Let $\mathcal{I}^\bullet $ be a K-injective complex of $\mathcal{O}$-modules. Let $\mathcal{L}^\bullet $ be a K-flat complex of $\mathcal{O}$-modules. Then $\mathop{\mathcal{H}\! \mathit{om}}\nolimits ^\bullet (\mathcal{L}^\bullet , \mathcal{I}^\bullet )$ is a K-injective complex of $\mathcal{O}$-modules.

**Proof.**
Namely, if $\mathcal{K}^\bullet $ is an acyclic complex of $\mathcal{O}$-modules, then

The first equality by (21.33.0.2). The second equality by Lemma 21.33.1. The third equality by (21.33.0.2). The final equality because $\text{Tot}(\mathcal{K}^\bullet \otimes _\mathcal {O} \mathcal{L}^\bullet )$ is acyclic because $\mathcal{L}^\bullet $ is K-flat (Definition 21.18.2) and because $\mathcal{I}^\bullet $ is K-injective. $\square$

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