have l2 : HasDerivAt (fun v => -v * u) (-u) x := by simpa only [neg_mul_comm] using hasDerivAt_mul_const (-u)
u x : ℝ
⊢ HasDerivAt (⇑(e u)) (-2 * ↑π * ↑u * I * (e u) x) x
u x : ℝ
l2 : HasDerivAt (fun v => -v * u) (-u) x
⊢ HasDerivAt (⇑(e u)) (-2 * ↑π * ↑u * I * (e u) x) x