proposition: Lemma fmmulA : associative fmmul.
proof: Proof. by move=> m1 m2 m3; rewrite !fmE catA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap