proposition: Lemma memJ_norm x y A : x \in 'N(A) -> (y ^ x \in A) = (y \in A).
proof: Proof. by move=> Nx; rewrite -{1}(normP Nx) memJ_conjg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)