Kerodon

$\Newextarrow{\xRightarrow}{5,5}{0x21D2}$
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$

Example 4.1.1.5. 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.