proposition: Lemma end0g_eq d : end0g d *+ 2 - oddg d = d.
proof: Proof. by rewrite mulrnDl addrA halfgK addrK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)