Remark 7.6.2.7. Let $\operatorname{\mathcal{C}}$ be an $\infty $-category and let $\sigma : \Delta ^1 \times \Delta ^1 \rightarrow \operatorname{\mathcal{C}}$ be a commutative square in $\operatorname{\mathcal{C}}$. Then $\sigma $ is a pullback square if and only if it is $U$-pullback square, where $U: \operatorname{\mathcal{C}}\rightarrow \Delta ^0$ is the projection map (see Example 7.1.6.3).
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$