Remark 6.3.7.10. Let $S$ be a simplicial set which can be written as a union of a collection of simplicial subsets $\{ S_{\alpha } \subseteq S \} $. If each $S_{\alpha }$ is nonsingular, then $S$ is nonsingular.
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$