proposition: Lemma memV_rcosetV x y : (y^-1 \in G :* x^-1) = (y \in x *: G).
proof: Proof. by rewrite -invg_lcoset memV_invg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)