Remark 1.2.1.4 (Transitivity). Let $S_{}$ be a simplicial set. If $S'_{} \subseteq S_{}$ is a summand of $S_{}$ and $S''_{} \subseteq S'_{}$ is a summand of $S'_{}$, then $S''_{}$ is a summand of $S_{}$.
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$