proposition: Lemma eq_gchop_halfg d p : halfg d = p -> gchop d p.
proof: Proof. by move <-; apply: gchop_halfg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)