no goals
𝕜 : Type u_1
E : Type u_2
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
a b : 𝕜
s : Set 𝕜
h : DifferentiableWithinAt 𝕜 (dslope f a) s b
⊢ DifferentiableWithinAt 𝕜 f s b
simpa only [id, sub_smul_dslope f a, sub_add_cancel] using
  ((differentiableWithinAt_id.sub_const a).smul h).add_const (f a)