∀ {m : Type u_1 → Type u_2} {β : Type u_1} [inst : MonadAttach m] {P : β → m (ULift.{u_1, 0} Bool)} (out : β),
  MonadAttach.CanReturn (P out) { down := true } →
    ((Std.Iterators.PostconditionT.attachLift ∘ P) out).Property { down := true }