# Kerodon

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Definition 7.1.6.1. Let $U: \operatorname{\mathcal{C}}\rightarrow \operatorname{\mathcal{D}}$ be a functor of $\infty$-categories. We say that an object $Y \in \operatorname{\mathcal{C}}$ is $U$-final if, for every object $X \in \operatorname{\mathcal{C}}$, the functor $U$ induces a homotopy equivalence

$\operatorname{Hom}_{\operatorname{\mathcal{C}}}(X,Y) \rightarrow \operatorname{Hom}_{\operatorname{\mathcal{D}}}( U(X), U(Y) ).$

We say that $Y$ is $U$-initial if, for every object $Z \in \operatorname{\mathcal{C}}$, the functor $U$ induces a homotopy equivalence

$\operatorname{Hom}_{\operatorname{\mathcal{C}}}(Y,Z) \rightarrow \operatorname{Hom}_{\operatorname{\mathcal{D}}}( U(Y), U(Z) ).$