∀ {L : FirstOrder.Language} {M : Type w} [inst : L.Structure M] {s : Set M} {p : M → Prop} {x : M},
  x ∈ (FirstOrder.Language.Substructure.closure L).toFun s →
    (∀ x ∈ s, p x) → (∀ {n : ℕ} (f : L.Functions n), FirstOrder.Language.ClosedUnder f (setOf p)) → p x