Lemma 15.73.3 (0A67)—The Stacks project

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Lemma 15.73.3. Let $R$ be a ring. Let $K, L, M$ be objects of $D(R)$ . There is a canonical morphism

$R\mathop{\mathrm{Hom}}\nolimits _ R(L, M) \otimes _ R^\mathbf {L} K \longrightarrow R\mathop{\mathrm{Hom}}\nolimits _ R(R\mathop{\mathrm{Hom}}\nolimits _ R(K, L), M)$

in $D(R)$ functorial in $K, L, M$ .

Proof. Choose a K-injective complex $I^\bullet$ representing $M$ , a K-injective complex $J^\bullet$ representing $L$ , and a K-flat complex $K^\bullet$ representing $K$ . The map is defined using the map

$\text{Tot}(\mathop{\mathrm{Hom}}\nolimits ^\bullet (J^\bullet , I^\bullet ) \otimes _ R K^\bullet ) \longrightarrow \mathop{\mathrm{Hom}}\nolimits ^\bullet (\mathop{\mathrm{Hom}}\nolimits ^\bullet (K^\bullet , J^\bullet ), I^\bullet )$

of Lemma 15.71.6. We omit the proof that this is functorial in all three objects of $D(R)$ . $\square$

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