Example 4.2.1.5. A morphism of simplicial sets $f: X \rightarrow S$ is a Kan fibration if and only if it is both a left fibration and a right fibration.

$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$

$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$

Example 4.2.1.5. A morphism of simplicial sets $f: X \rightarrow S$ is a Kan fibration if and only if it is both a left fibration and a right fibration.