Remark 3.1.5.16 (Two-out-of-Three). Let $f: X_{} \rightarrow Y_{}$ and $g: Y_{} \rightarrow Z_{}$ be morphisms of simplicial sets. If any two of the morphisms $f$, $g$, and $g \circ f$ are weak homotopy equivalences, then so is the third.

$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$