∀ {𝕜 : Type u_1} {B : Type u_2} {F : Type u_4} {E : B → Type u_6} [inst : TopologicalSpace B]
  [inst_1 : TopologicalSpace (Bundle.TotalSpace F E)] [inst_2 : (x : B) → TopologicalSpace (E x)]
  [inst_3 : NormedAddCommGroup F] [inst_4 : NontriviallyNormedField 𝕜] [inst_5 : NormedSpace 𝕜 F]
  [inst_6 : FiberBundle F E] [inst_7 : (x : B) → AddCommGroup (E x)] [inst_8 : (x : B) → Module 𝕜 (E x)]
  [VectorBundle 𝕜 F E] {HB : Type u_7} [inst_10 : TopologicalSpace HB] [inst_11 : ChartedSpace HB B] {EB : Type u_8}
  [inst_12 : NormedAddCommGroup EB] [inst_13 : NormedSpace 𝕜 EB] {I : ModelWithCorners 𝕜 EB HB} {ι : Type u_9}
  {s : Finset ι} {t : ι → (x : B) → E x} {x₀ : B},
  (∀ (i : ι), MDifferentiableAt I (I.prod (modelWithCornersSelf 𝕜 F)) (fun x => Bundle.TotalSpace.mk' F x (t i x)) x₀) →
    MDifferentiableAt I (I.prod (modelWithCornersSelf 𝕜 F)) (fun x => Bundle.TotalSpace.mk' F x (∑ i ∈ s, t i x)) x₀