∀ (X : Type u_1) [inst : NormedAddCommGroup X] [inst_1 : NormedSpace ℝ X] {n : ℕ} {u : Set (EuclideanSpace ℝ (Fin n))},
  IsOpen u →
    ∀ (x x_1 : EuclideanSpace ℝ (Fin n) → X), Set.EqOn x x_1 u → (ContDiffOn ℝ (↑⊤) x u ↔ ContDiffOn ℝ (↑⊤) x_1 u)