This is a basic issue of PL topology that I assume must be true, but I can't find a written reference: is a convex open PL subset of $\mathbb R^n$ PL homeomorphic to $\mathbb R^n$? I've scanned through RourkeSanderson, Hudson, Zeeman, and Stallings, but can't quite find it in there. I'd appreciate a quotable reference if possible.
