∀ {𝕜 : Type u_1} [inst : NontriviallyNormedField 𝕜] {E : Type u_2} [inst_1 : NormedAddCommGroup E]
  [inst_2 : NormedSpace 𝕜 E] {a b : E} {x : 𝕜}, HasStrictDerivAt (⇑(AffineMap.lineMap a b)) (b - a) x