have l4 : Differentiable ℝ f := f.differentiable
f : W21
u : ℝ
l1 : Integrable (fun x => (↑π ^ 2)⁻¹ * 4⁻¹ * deriv (deriv f.toFun) x) volume
⊢ (1 + ↑u ^ 2) * 𝓕 f.toFun u = 𝓕 (fun u => f.toFun u - 1 / (4 * ↑π ^ 2) * deriv^[2] f.toFun u) u
f : W21
u : ℝ
l1 : Integrable (fun x => (↑π ^ 2)⁻¹ * 4⁻¹ * deriv (deriv f.toFun) x) volume
l4 : Differentiable ℝ f.toFun
⊢ (1 + ↑u ^ 2) * 𝓕 f.toFun u = 𝓕 (fun u => f.toFun u - 1 / (4 * ↑π ^ 2) * deriv^[2] f.toFun u) u