∀ {𝕜 : Type u_1} {E : Type u_2} [inst : NontriviallyNormedField 𝕜] [inst_1 : NormedAddCommGroup E]
  [inst_2 : NormedSpace 𝕜 E] {f : 𝕜 → E} {a : 𝕜} {s : Set 𝕜}, DifferentiableOn 𝕜 (dslope f a) s → DifferentiableOn 𝕜 f s