proposition: Lemma garea_refine_rect r : garea (refine_rect r) = (garea r).*2.*2.
proof: Proof. suffices{r} Dzwidth2 x y: zwidth (x *+ 2) (y *+ 2) = (zwidth x y).*2. by case: r => x0 x1 y0 y1; rewrite doubleMl doubleMr -!Dzwidth2. by rewrite /zwidth -mulrnBl; case: (y - x) => n //=; rewrite addnn. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)