∀ {𝕜 : Type u} [inst : NontriviallyNormedField 𝕜] {F : Type v} [inst_1 : NormedAddCommGroup F]
  [inst_2 : NormedSpace 𝕜 F] {f : 𝕜 → F} {f' : F} {x : 𝕜} {s : Set 𝕜},
  x ∉ s → (HasDerivWithinAt f f' s x ↔ Filter.Tendsto (slope f x) (nhdsWithin x s) (nhds f'))