Definition 2.2.8.5. A $(2,1)$-category is a $2$-category $\operatorname{\mathcal{C}}$ with the property that every $2$-morphism in $\operatorname{\mathcal{C}}$ is invertible.
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
Definition 2.2.8.5. A $(2,1)$-category is a $2$-category $\operatorname{\mathcal{C}}$ with the property that every $2$-morphism in $\operatorname{\mathcal{C}}$ is invertible.