∀ {𝕜 : Type u} [inst : NontriviallyNormedField 𝕜] {F : Type v} [inst_1 : NormedAddCommGroup F]
  [inst_2 : NormedSpace 𝕜 F] {f : 𝕜 → F} {x : 𝕜} {𝕜' : Type u_2} [inst_3 : NormedRing 𝕜'] [inst_4 : NormedAlgebra 𝕜 𝕜']
  [inst_5 : Module 𝕜' F] [IsBoundedSMul 𝕜' F] [IsScalarTower 𝕜 𝕜' F] {c : 𝕜 → 𝕜'},
  DifferentiableAt 𝕜 c x → DifferentiableAt 𝕜 f x → deriv (c • f) x = c x • deriv f x + deriv c x • f x