proposition: Lemma subg_invP : left_inverse subg_one subg_inv subg_mul.
proof: Proof. by move=> u; apply: val_inj; apply: mulVg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)