-- Mathlib/Topology/Category/TopCat/Limits/Pullbacks.lean
theorem pullback_map_isEmbedding {W X Y Z S T : TopCat.{u}} (f₁ : W ⟶ S) (f₂ : X ⟶ S)
    (g₁ : Y ⟶ T) (g₂ : Z ⟶ T) {i₁ : W ⟶ Y} {i₂ : X ⟶ Z} (H₁ : IsEmbedding i₁)
    (H₂ : IsEmbedding i₂) (i₃ : S ⟶ T) (eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁) (eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂) :
    IsEmbedding (pullback.map f₁ f₂ g₁ g₂ i₁ i₂ i₃ eq₁ eq₂)

Proof state:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
⊢ IsEmbedding ⇑(ConcreteCategory.hom (prod.lift (pullback.fst f₁ f₂) (pullback.snd f₁ f₂) ≫ prod.map i₁ i₂))

Tactic:
rw [coe_comp]

Result:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
⊢ IsEmbedding
    (⇑(ConcreteCategory.hom (prod.map i₁ i₂)) ∘
      ⇑(ConcreteCategory.hom (prod.lift (pullback.fst f₁ f₂) (pullback.snd f₁ f₂))))

Proof state:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
⊢ IsEmbedding
    (⇑(ConcreteCategory.hom (prod.lift (pullback.fst g₁ g₂) (pullback.snd g₁ g₂))) ∘
      ⇑(ConcreteCategory.hom (pullback.map f₁ f₂ g₁ g₂ i₁ i₂ i₃ eq₁ eq₂)))

Tactic:
suffices
  IsEmbedding (prod.lift (pullback.fst f₁ f₂) (pullback.snd f₁ f₂) ≫ Limits.prod.map i₁ i₂) by
  simpa [← coe_comp] using this

Result:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
⊢ IsEmbedding ⇑(ConcreteCategory.hom (prod.lift (pullback.fst f₁ f₂) (pullback.snd f₁ f₂) ≫ prod.map i₁ i₂))

Proof state:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
⊢ IsEmbedding ⇑(ConcreteCategory.hom (pullback.map f₁ f₂ g₁ g₂ i₁ i₂ i₃ eq₁ eq₂))

Tactic:
refine .of_comp (ContinuousMap.continuous_toFun _)
  (show Continuous (prod.lift (pullback.fst g₁ g₂) (pullback.snd g₁ g₂)) from
      ContinuousMap.continuous_toFun _)
    ?_

Result:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
⊢ IsEmbedding
    (⇑(ConcreteCategory.hom (prod.lift (pullback.fst g₁ g₂) (pullback.snd g₁ g₂))) ∘
      ⇑(ConcreteCategory.hom (pullback.map f₁ f₂ g₁ g₂ i₁ i₂ i₃ eq₁ eq₂)))

Proof state:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
this : IsEmbedding ⇑(ConcreteCategory.hom (prod.lift (pullback.fst f₁ f₂) (pullback.snd f₁ f₂) ≫ prod.map i₁ i₂))
⊢ IsEmbedding
    (⇑(ConcreteCategory.hom (prod.lift (pullback.fst g₁ g₂) (pullback.snd g₁ g₂))) ∘
      ⇑(ConcreteCategory.hom (pullback.map f₁ f₂ g₁ g₂ i₁ i₂ i₃ eq₁ eq₂)))

Tactic:
simpa [← coe_comp] using this

Result:
no goals

Proof state:
W X Y Z S T : TopCat
f₁ : W ⟶ S
f₂ : X ⟶ S
g₁ : Y ⟶ T
g₂ : Z ⟶ T
i₁ : W ⟶ Y
i₂ : X ⟶ Z
H₁ : IsEmbedding ⇑(ConcreteCategory.hom i₁)
H₂ : IsEmbedding ⇑(ConcreteCategory.hom i₂)
i₃ : S ⟶ T
eq₁ : f₁ ≫ i₃ = i₁ ≫ g₁
eq₂ : f₂ ≫ i₃ = i₂ ≫ g₂
⊢ IsEmbedding
    (⇑(ConcreteCategory.hom (prod.map i₁ i₂)) ∘
      ⇑(ConcreteCategory.hom (prod.lift (pullback.fst f₁ f₂) (pullback.snd f₁ f₂))))

Tactic:
exact (isEmbedding_prodMap H₁ H₂).comp (isEmbedding_pullback_to_prod _ _)

Result:
no goals