TITLE: What's a coproduct in slice category?
QUESTION [7 upvotes]: We know that product in slice category $\mathcal{C}\downarrow x$ is pullback in $\mathcal{C}$, but what's a coproduct in $\mathcal{C}\downarrow x$ (described in $\mathcal{C}$)? I tried to picture it as a limit or colimit, without success.

REPLY [3 votes]: The coproduct of $y \to x$ and $z \to x$ is $y \sqcup z \to x$. (Note that the forgetful functor from the slice category back down to $C$ has a right adjoint whenever $C$ has all products by $x$, and in that case it preserves all colimits. But actually it just always preserves all colimits.)