proposition: Lemma sub_mem_approx s (gr1 gr2 : gregion) : subpred gr1 gr2 -> subregion (mem_approx s gr1) (mem_approx s gr2).
proof: Proof. by move=> Hgr12 z [p Dp Hp]; exists p; auto. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype tuple path fingraph bigop order ssralg) mathcomp(ssrnum ssrint div intdiv) fourcolor(hypermap geometry coloring grid matte) fourcolor(real realplane) Coq(Setoid Morphisms) fourcolor(realsyntax realprop)