proposition: Lemma FA_small m n: n < m -> FA m n = 0.
proof: Proof. by rewrite /FA;case:m => // m /= ->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)