∀ {𝕜 : Type u} [inst : NontriviallyNormedField 𝕜] {F : Type v} [inst_1 : NormedAddCommGroup F]
  [inst_2 : NormedSpace 𝕜 F] {f : 𝕜 → F} {a b : 𝕜},
  DifferentiableAt 𝕜 f a ↔ DifferentiableAt 𝕜 (fun x => f (b - x)) (b - a)