-- Mathlib/Topology/FiberBundle/Constructions.lean
theorem Prod.continuous_to_fun : ContinuousOn (Prod.toFun' e₁ e₂)
    (π (F₁ × F₂) (E₁ ×ᵇ E₂) ⁻¹' (e₁.baseSet ∩ e₂.baseSet))

Proof state:
case refine_2.mk.mk.intro
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
hf₃ : Continuous f₃
b : B
v₁ : E₁ b
v₂ : E₂ b
hb₁ : { proj := b, snd := (v₁, v₂) }.proj ∈ e₁.baseSet
right✝ : { proj := b, snd := (v₁, v₂) }.proj ∈ e₂.baseSet
⊢ toFun' e₁ e₂ { proj := b, snd := (v₁, v₂) } = ((f₃ ∘ f₂) ∘ f₁) { proj := b, snd := (v₁, v₂) }

Tactic:
simp only [f₁, f₂, f₃, Prod.toFun', Prod.mk.inj_iff, Function.comp_apply, and_true]

Result:
case refine_2.mk.mk.intro
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
hf₃ : Continuous f₃
b : B
v₁ : E₁ b
v₂ : E₂ b
hb₁ : { proj := b, snd := (v₁, v₂) }.proj ∈ e₁.baseSet
right✝ : { proj := b, snd := (v₁, v₂) }.proj ∈ e₂.baseSet
⊢ b = (↑e₁ { proj := b, snd := v₁ }).1

Proof state:
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
hf₃ : Continuous f₃
⊢ ContinuousOn (toFun' e₁ e₂) (TotalSpace.proj ⁻¹' (e₁.baseSet ∩ e₂.baseSet))

Tactic:
refine ((hf₃.comp_continuousOn hf₂).comp hf₁.continuousOn ?_).congr ?_

Result:
case refine_1
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
hf₃ : Continuous f₃
⊢ MapsTo f₁ (TotalSpace.proj ⁻¹' (e₁.baseSet ∩ e₂.baseSet)) (e₁.source ×ˢ e₂.source)

case refine_2
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
hf₃ : Continuous f₃
⊢ EqOn (toFun' e₁ e₂) ((f₃ ∘ f₂) ∘ f₁) (TotalSpace.proj ⁻¹' (e₁.baseSet ∩ e₂.baseSet))

Proof state:
case refine_2
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
hf₃ : Continuous f₃
⊢ EqOn (toFun' e₁ e₂) ((f₃ ∘ f₂) ∘ f₁) (TotalSpace.proj ⁻¹' (e₁.baseSet ∩ e₂.baseSet))

Tactic:
rintro ⟨b, v₁, v₂⟩ ⟨hb₁, _⟩

Result:
case refine_2.mk.mk.intro
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
hf₃ : Continuous f₃
b : B
v₁ : E₁ b
v₂ : E₂ b
hb₁ : { proj := b, snd := (v₁, v₂) }.proj ∈ e₁.baseSet
right✝ : { proj := b, snd := (v₁, v₂) }.proj ∈ e₂.baseSet
⊢ toFun' e₁ e₂ { proj := b, snd := (v₁, v₂) } = ((f₃ ∘ f₂) ∘ f₁) { proj := b, snd := (v₁, v₂) }

Proof state:
B : Type u_1
inst✝⁴ : TopologicalSpace B
F₁ : Type u_2
inst✝³ : TopologicalSpace F₁
E₁ : B → Type u_3
inst✝² : TopologicalSpace (TotalSpace F₁ E₁)
F₂ : Type u_4
inst✝¹ : TopologicalSpace F₂
E₂ : B → Type u_5
inst✝ : TopologicalSpace (TotalSpace F₂ E₂)
e₁ : Trivialization F₁ TotalSpace.proj
e₂ : Trivialization F₂ TotalSpace.proj
f₁ : (TotalSpace (F₁ × F₂) fun x => E₁ x × E₂ x) → TotalSpace F₁ E₁ × TotalSpace F₂ E₂ :=
  fun p => ({ proj := p.proj, snd := p.snd.1 }, { proj := p.proj, snd := p.snd.2 })
f₂ : TotalSpace F₁ E₁ × TotalSpace F₂ E₂ → (B × F₁) × B × F₂ := fun p => (↑e₁ p.1, ↑e₂ p.2)
f₃ : (B × F₁) × B × F₂ → B × F₁ × F₂ := fun p => (p.1.1, p.1.2, p.2.2)
hf₁ : Continuous f₁
hf₂ : ContinuousOn f₂ (e₁.source ×ˢ e₂.source)
⊢ Continuous f₃

Tactic:
fun_prop

Result:
no goals