proposition: Lemma neq_halfg_edge p : (halfg p == halfg (gedge p)) = false.
proof: Proof. by rewrite halfg_edge -subr_eq0 opprD addNKr; case: oddgP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)