proposition: Lemma in_gchop1_rect d : gchop1_rect d =1 predI r (gchop1 d).
proof: Proof. apply: in_gchop_rect. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)