Exercise 4.2.5.5. Let $f: X \rightarrow S$ be a left covering morphism of simplicial sets. Show that, for any left anodyne morphism $i: A \hookrightarrow B$, the induced map
\[ \rho : \operatorname{Fun}( B_{}, X_{} ) \rightarrow \operatorname{Fun}( B_{}, S_{} ) \times _{ \operatorname{Fun}( A_{}, S_{} )} \operatorname{Fun}( A_{}, X_{} ) \]
is an isomorphism of simplicial sets.