Example 4.5.8.4. Let $X$ and $Y$ be simplicial sets. If $X$ is empty, then the blunt join $X \diamond Y$ can be identified with $Y$. If $Y$ is empty, then the blunt join $X \diamond Y$ can be identified with $X$. In either case, the comparison map $c_{X,Y}: X \diamond Y \rightarrow X \star Y$ is an isomorphism of simplicial sets.
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$