proposition: Lemma conjSg A B x : (A :^ x \subset B :^ x) = (A \subset B).
proof: Proof. by rewrite !conjsgE lcosetS rcosetS. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)