Corollary 3.3.3.4. The functor $\operatorname{Ex}: \operatorname{Set_{\Delta }}\rightarrow \operatorname{Set_{\Delta }}$ admits a left adjoint, given by the construction $X \mapsto \operatorname{Sd}(X)$.
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$