proposition: Lemma unit_muluA : associative unit_mul.
proof: Proof. by move=> u v w; apply/val_inj/mulrA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype finset fingroup morphism perm action) mathcomp(ssralg countalg)