Lemma 15.85.3. Let $\mathcal{D}$ be a triangulated category. Let $(K_ n)$ be an inverse system of objects of $\mathcal{D}$. Let $K$ be a derived limit of the system $(K_ n)$. Then for every $L$ in $\mathcal{D}$ we have a short exact sequence

$0 \to R^1\mathop{\mathrm{lim}}\nolimits \mathop{\mathrm{Hom}}\nolimits _\mathcal {D}(L, K_ n[-1]) \to \mathop{\mathrm{Hom}}\nolimits _\mathcal {D}(L, K) \to \mathop{\mathrm{lim}}\nolimits \mathop{\mathrm{Hom}}\nolimits _\mathcal {D}(L, K_ n) \to 0$

Proof. This follows from Derived Categories, Definition 13.34.1 and Lemma 13.4.2, and the description of $\mathop{\mathrm{lim}}\nolimits$ and $R^1\mathop{\mathrm{lim}}\nolimits$ in Lemma 15.85.1 above. $\square$

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