proposition: Lemma area_Dr a b b': area a (b+b') = ((area a b) + (area a b'))%R.
proof: Proof. by rewrite /area /pair_add /= !PoszD !mulrDr addrACA opprD. 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)