proposition: Lemma size_enum_grect r : size (enum_grect r) = garea r.
proof: Proof. by case: r => x0 x1 y0 y1; rewrite size_allpairs !size_zspan. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)