proposition: Lemma normalYr G H : (H <| G <*> H) = (G \subset 'N(H)).
proof: Proof. by rewrite joingC normalYl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)