proposition: Lemma area_sym a b : area a b = - (area b a).
proof: Proof. by rewrite /area opprD addrC mulrC opprK (mulrC (b.1)%:Z). 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)