proposition: Lemma gchop_rect_sub d : subpred (gchop_rect d) r.
proof: Proof. by move=> p; rewrite in_gchop_rect => /andP[]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)