proposition: Lemma fgmul1g : left_id fgone fgmul.
proof: Proof. move=> g; rewrite fgmulUg [RHS]monalgE. by apply/eq_bigr=> kg _; rewrite mul1r mul1m. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap