Example 4.3.2.4. Let $\operatorname{\mathcal{C}}$ and $\operatorname{\mathcal{D}}$ be categories. If $\operatorname{\mathcal{D}}$ is empty, then the inclusion map $\operatorname{\mathcal{C}}\hookrightarrow \operatorname{\mathcal{C}}\star \operatorname{\mathcal{D}}$ is an isomorphism of categories.
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$