# Kerodon

$\Newextarrow{\xRightarrow}{5,5}{0x21D2}$

Remark 4.2.1.3. Let $f: X_{} \rightarrow S_{}$ be a morphism of simplicial sets. Then $f$ is a left fibration if and only if the opposite morphism $f^{\operatorname{op}}: X_{}^{\operatorname{op}} \rightarrow S_{}^{\operatorname{op}}$ is a right fibration.