refine ⟨fun H ↦ ?_, ofReal_comp⟩
𝕂 : Type u_1
inst✝ : _root_.RCLike 𝕂
z : ℝ
f : ℝ → ℝ
⊢ DifferentiableAt ℝ (fun y => ↑(f y)) z ↔ DifferentiableAt ℝ f z
𝕂 : Type u_1
inst✝ : _root_.RCLike 𝕂
z : ℝ
f : ℝ → ℝ
H : DifferentiableAt ℝ (fun y => ↑(f y)) z
⊢ DifferentiableAt ℝ f z