# Kerodon

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Example 4.5.9.5. Let $U: \operatorname{\mathcal{D}}\rightarrow \operatorname{\mathcal{C}}$ be a morphism of simplicial sets, and let $V: \operatorname{\mathcal{D}}\rightarrow \operatorname{\mathcal{D}}$ be the identity map. Then the projection map $\operatorname{Res}_{\operatorname{\mathcal{D}}/\operatorname{\mathcal{C}}}( \operatorname{\mathcal{D}}) \rightarrow \operatorname{\mathcal{C}}$ is an isomorphism.