∀ {𝕜 : Type u_1} [inst : NontriviallyNormedField 𝕜] {F : Type u_2} [inst_1 : NormedAddCommGroup F]
  [inst_2 : NormedSpace 𝕜 F] {n : ℕ} {x : 𝕜} {s : Set 𝕜},
  x ∈ s →
    UniqueDiffOn 𝕜 s →
      ∀ {f g : 𝕜 → F},
        ContDiffWithinAt 𝕜 (↑n) f s x →
          ContDiffWithinAt 𝕜 (↑n) g s x →
            iteratedDerivWithin n (f + g) s x = iteratedDerivWithin n f s x + iteratedDerivWithin n g s x