proposition: Lemma area_Dl a a' b: area (a+a') b = ((area a b) + (area a' b))%R.
proof: Proof. by rewrite area_sym area_Dr opprD - !area_sym. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype order bigop ssralg) mathcomp(div ssrnum ssrint rat prime path binomial) mathcomp(tuple finset) gaia(fibm)