/-- The product of two vector bundles is a vector bundle. -/
instance VectorBundle.prod [VectorBundle 𝕜 F₁ E₁] [VectorBundle 𝕜 F₂ E₂] :
    VectorBundle 𝕜 (F₁ × F₂) (E₁ ×ᵇ E₂) where
  trivialization_linear' := by
    rintro _ ⟨e₁, e₂, he₁, he₂, rfl⟩; skip
    infer_instance
  continuousOn_coordChange' := by
    rintro _ _ ⟨e₁, e₂, he₁, he₂, rfl⟩ ⟨e₁', e₂', he₁', he₂', rfl⟩; skip
    refine' (((continuousOn_coordChange 𝕜 e₁ e₁').mono _).prod_mapL 𝕜
      ((continuousOn_coordChange 𝕜 e₂ e₂').mono _)).congr _ <;>
      dsimp only [baseSet_prod, mfld_simps]
    · mfld_set_tac
    · mfld_set_tac
    · rintro b hb
      rw [ContinuousLinearMap.ext_iff]
      rintro ⟨v₁, v₂⟩
      show (e₁.prod e₂).coordChangeL 𝕜 (e₁'.prod e₂') b (v₁, v₂) =
        (e₁.coordChangeL 𝕜 e₁' b v₁, e₂.coordChangeL 𝕜 e₂' b v₂)
      rw [e₁.coordChangeL_apply e₁', e₂.coordChangeL_apply e₂', (e₁.prod e₂).coordChangeL_apply']
      

Proof state:
case mk.intro.intro.intro.intro.mk.intro.intro.intro.intro.refine'_3.mk
𝕜 : Type u_1
B : Type u_2
inst✝¹⁷ : NontriviallyNormedField 𝕜
inst✝¹⁶ : TopologicalSpace B
F₁ : Type u_3
inst✝¹⁵ : NormedAddCommGroup F₁
inst✝¹⁴ : NormedSpace 𝕜 F₁
E₁ : B → Type u_4
inst✝¹³ : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_5
inst✝¹² : NormedAddCommGroup F₂
inst✝¹¹ : NormedSpace 𝕜 F₂
E₂ : B → Type u_6
inst✝¹⁰ : TopologicalSpace (TotalSpace F₂ E₂)
inst✝⁹ : (x : B) → AddCommMonoid (E₁ x)
inst✝⁸ : (x : B) → Module 𝕜 (E₁ x)
inst✝⁷ : (x : B) → AddCommMonoid (E₂ x)
inst✝⁶ : (x : B) → Module 𝕜 (E₂ x)
inst✝⁵ : (x : B) → TopologicalSpace (E₁ x)
inst✝⁴ : (x : B) → TopologicalSpace (E₂ x)
inst✝³ : FiberBundle F₁ E₁
inst✝² : FiberBundle F₂ E₂
inst✝¹ : VectorBundle 𝕜 F₁ E₁
inst✝ : VectorBundle 𝕜 F₂ E₂
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
he₁ : MemTrivializationAtlas e₁
he₂ : MemTrivializationAtlas e₂
e₁' : Trivialization F₁ TotalSpace.proj
e₂' : Trivialization F₂ TotalSpace.proj
he₁' : MemTrivializationAtlas e₁'
he₂' : MemTrivializationAtlas e₂'
b : B
hb : b ∈ e₁.baseSet ∩ e₂.baseSet ∩ (e₁'.baseSet ∩ e₂'.baseSet)
v₁ : F₁
v₂ : F₂
⊢ (↑(Trivialization.prod e₁' e₂')
        (↑(PartialHomeomorph.symm (Trivialization.prod e₁ e₂).toPartialHomeomorph) (b, v₁, v₂))).2 =
    ((↑e₁' { proj := b, snd := Trivialization.symm e₁ b v₁ }).2,
      (↑e₂' { proj := b, snd := Trivialization.symm e₂ b v₂ }).2)
case mk.intro.intro.intro.intro.mk.intro.intro.intro.intro.refine'_3.mk.hb
𝕜 : Type u_1
B : Type u_2
inst✝¹⁷ : NontriviallyNormedField 𝕜
inst✝¹⁶ : TopologicalSpace B
F₁ : Type u_3
inst✝¹⁵ : NormedAddCommGroup F₁
inst✝¹⁴ : NormedSpace 𝕜 F₁
E₁ : B → Type u_4
inst✝¹³ : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_5
inst✝¹² : NormedAddCommGroup F₂
inst✝¹¹ : NormedSpace 𝕜 F₂
E₂ : B → Type u_6
inst✝¹⁰ : TopologicalSpace (TotalSpace F₂ E₂)
inst✝⁹ : (x : B) → AddCommMonoid (E₁ x)
inst✝⁸ : (x : B) → Module 𝕜 (E₁ x)
inst✝⁷ : (x : B) → AddCommMonoid (E₂ x)
inst✝⁶ : (x : B) → Module 𝕜 (E₂ x)
inst✝⁵ : (x : B) → TopologicalSpace (E₁ x)
inst✝⁴ : (x : B) → TopologicalSpace (E₂ x)
inst✝³ : FiberBundle F₁ E₁
inst✝² : FiberBundle F₂ E₂
inst✝¹ : VectorBundle 𝕜 F₁ E₁
inst✝ : VectorBundle 𝕜 F₂ E₂
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
he₁ : MemTrivializationAtlas e₁
he₂ : MemTrivializationAtlas e₂
e₁' : Trivialization F₁ TotalSpace.proj
e₂' : Trivialization F₂ TotalSpace.proj
he₁' : MemTrivializationAtlas e₁'
he₂' : MemTrivializationAtlas e₂'
b : B
hb : b ∈ e₁.baseSet ∩ e₂.baseSet ∩ (e₁'.baseSet ∩ e₂'.baseSet)
v₁ : F₁
v₂ : F₂
⊢ b ∈ (Trivialization.prod e₁ e₂).baseSet ∩ (Trivialization.prod e₁' e₂').baseSet
case mk.intro.intro.intro.intro.mk.intro.intro.intro.intro.refine'_3.mk.hb
𝕜 : Type u_1
B : Type u_2
inst✝¹⁷ : NontriviallyNormedField 𝕜
inst✝¹⁶ : TopologicalSpace B
F₁ : Type u_3
inst✝¹⁵ : NormedAddCommGroup F₁
inst✝¹⁴ : NormedSpace 𝕜 F₁
E₁ : B → Type u_4
inst✝¹³ : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_5
inst✝¹² : NormedAddCommGroup F₂
inst✝¹¹ : NormedSpace 𝕜 F₂
E₂ : B → Type u_6
inst✝¹⁰ : TopologicalSpace (TotalSpace F₂ E₂)
inst✝⁹ : (x : B) → AddCommMonoid (E₁ x)
inst✝⁸ : (x : B) → Module 𝕜 (E₁ x)
inst✝⁷ : (x : B) → AddCommMonoid (E₂ x)
inst✝⁶ : (x : B) → Module 𝕜 (E₂ x)
inst✝⁵ : (x : B) → TopologicalSpace (E₁ x)
inst✝⁴ : (x : B) → TopologicalSpace (E₂ x)
inst✝³ : FiberBundle F₁ E₁
inst✝² : FiberBundle F₂ E₂
inst✝¹ : VectorBundle 𝕜 F₁ E₁
inst✝ : VectorBundle 𝕜 F₂ E₂
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
he₁ : MemTrivializationAtlas e₁
he₂ : MemTrivializationAtlas e₂
e₁' : Trivialization F₁ TotalSpace.proj
e₂' : Trivialization F₂ TotalSpace.proj
he₁' : MemTrivializationAtlas e₁'
he₂' : MemTrivializationAtlas e₂'
b : B
hb : b ∈ e₁.baseSet ∩ e₂.baseSet ∩ (e₁'.baseSet ∩ e₂'.baseSet)
v₁ : F₁
v₂ : F₂
⊢ b ∈ e₂.baseSet ∩ e₂'.baseSet
case mk.intro.intro.intro.intro.mk.intro.intro.intro.intro.refine'_3.mk.hb
𝕜 : Type u_1
B : Type u_2
inst✝¹⁷ : NontriviallyNormedField 𝕜
inst✝¹⁶ : TopologicalSpace B
F₁ : Type u_3
inst✝¹⁵ : NormedAddCommGroup F₁
inst✝¹⁴ : NormedSpace 𝕜 F₁
E₁ : B → Type u_4
inst✝¹³ : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_5
inst✝¹² : NormedAddCommGroup F₂
inst✝¹¹ : NormedSpace 𝕜 F₂
E₂ : B → Type u_6
inst✝¹⁰ : TopologicalSpace (TotalSpace F₂ E₂)
inst✝⁹ : (x : B) → AddCommMonoid (E₁ x)
inst✝⁸ : (x : B) → Module 𝕜 (E₁ x)
inst✝⁷ : (x : B) → AddCommMonoid (E₂ x)
inst✝⁶ : (x : B) → Module 𝕜 (E₂ x)
inst✝⁵ : (x : B) → TopologicalSpace (E₁ x)
inst✝⁴ : (x : B) → TopologicalSpace (E₂ x)
inst✝³ : FiberBundle F₁ E₁
inst✝² : FiberBundle F₂ E₂
inst✝¹ : VectorBundle 𝕜 F₁ E₁
inst✝ : VectorBundle 𝕜 F₂ E₂
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
he₁ : MemTrivializationAtlas e₁
he₂ : MemTrivializationAtlas e₂
e₁' : Trivialization F₁ TotalSpace.proj
e₂' : Trivialization F₂ TotalSpace.proj
he₁' : MemTrivializationAtlas e₁'
he₂' : MemTrivializationAtlas e₂'
b : B
hb : b ∈ e₁.baseSet ∩ e₂.baseSet ∩ (e₁'.baseSet ∩ e₂'.baseSet)
v₁ : F₁
v₂ : F₂
⊢ b ∈ e₁.baseSet ∩ e₁'.baseSet

Next tactic:
exacts [rfl, hb, ⟨hb.1.2, hb.2.2⟩, ⟨hb.1.1, hb.2.1⟩]