proposition: Lemma fmM m1 m2 : (m1 * m2)%M = (m1 ++ m2) :> seq I.
proof: Proof. by rewrite /mmul /mul /= fmmulE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap