Remark 1.2.4.2. Roughly speaking, one can think of the horn $\Lambda ^{n}_{i}$ as obtained from the $n$-simplex $\Delta ^ n$ by removing its interior together with the face opposite its $i$th vertex (see Remark 1.2.4.6).
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$