proposition: Lemma mulGSgid A x : x \in A -> A \subset G -> G * A = G.
proof: Proof. rewrite -memV_invg -invSg invGid => Ax sAG. by apply: invg_inj; rewrite invMg invGid (mulSgGid Ax). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)