# Kerodon

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Proposition 7.3.1.14 (Change of Diagram). Let $F: \operatorname{\mathcal{C}}\rightarrow \operatorname{\mathcal{D}}$ be a functor of $\infty$-categories, let $\delta : K \rightarrow \operatorname{\mathcal{C}}$ and $F_0: K \rightarrow \operatorname{\mathcal{D}}$ be diagrams, and let $\epsilon : K' \rightarrow K$ be a categorical equivalence of simplicial sets. Then:

$(1)$

A natural transformation $\alpha : F \circ \delta \rightarrow F_0$ exhibits $F$ as a right Kan extension of $F_0$ along $\delta$ if and only if the induced transformation $\alpha ': F \circ (\delta \circ \epsilon ) \rightarrow F_0 \circ \epsilon$ exhibits $F$ as a right Kan extension of $F_0 \circ \epsilon$ along $\delta \circ \epsilon$.

$(2)$

A natural transformation $\beta : F_0 \rightarrow F \circ \delta$ exhibits $F$ as a left Kan extension of $F_0$ along $\delta$ if and only if the induced transformation $\beta ': F_0 \circ \epsilon \rightarrow F \circ (\delta \circ \epsilon )$ exhibits $F$ as a left Kan extension of $F_0 \circ \epsilon$ along $\delta \circ \epsilon$.

Proof. We will prove $(1)$; the proof of $(2)$ is similar. Fix an object $C \in \operatorname{\mathcal{C}}$. Since $\epsilon$ is a categorical equivalence and the projection map $\operatorname{\mathcal{C}}_{C/} \rightarrow \operatorname{\mathcal{C}}$ is a left fibration (Proposition 4.3.6.1), it follows that the induced map $\epsilon _{/C}: K' \times _{\operatorname{\mathcal{C}}} \operatorname{\mathcal{C}}_{C/} \rightarrow K \times _{\operatorname{\mathcal{C}}} \operatorname{\mathcal{C}}_{C/}$ is also a categorical equivalence of simplicial sets (Corollary 5.7.7.6). In particular, $\epsilon$ is left cofinal (Corollary 7.2.1.13). Applying Corollary 7.2.2.3, we see that the natural transformation $\alpha$ satisfies condition $(\ast _ C)$ of Definition 7.3.1.2 if and only if $\alpha '$ satisfies condition $(\ast _ C)$. The desired result now follows by allowing the object $C \in \operatorname{\mathcal{C}}$ to vary. $\square$