proposition: Lemma pair_addC a b: a + b = b + a.
proof: Proof. by rewrite /pair_add addnC (addnC a.2). 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)