Courant and Robbins provide an accessible proof.
According to Lyusternik Convex Figures and Polyhedra, the theorem was first proved by a Lettish mathematician named Bol. No references are provided. Anyone know what this is about?--192.35.35.36 00:08, 18 Feb 2005 (UTC)
Proofs
Why is wikipedia not the place to reroduce a long proof? --anon