Module: Mathlib.AlgebraicGeometry.Pullbacks

Goal state before:
pp: case h₁
X Y Z : Scheme
𝒰✝ : X.OpenCover
f✝ : X ⟶ Z
g : Y ⟶ Z
inst✝ : ∀ (i : 𝒰✝.I₀), HasPullback (𝒰✝.f i ≫ f✝) g
s : PullbackCone f✝ g
f : X ⟶ Y
𝒰 : Y.OpenCover
𝒱 : (i : (Precoverage.ZeroHypercover.pullback₁ f 𝒰).I₀) → ((Precoverage.ZeroHypercover.pullback₁ f 𝒰).X i).OpenCover
i : (openCoverOfBase 𝒰 f f).I₀
j : (𝒱 i).I₀
H :
  pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
      pullback.snd ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) =
    pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
      pullback.fst ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i))
⊢ pullback.map (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) (pullback.diagonal f)
        (pullback.map ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) f f
          ((𝒱 i).f j ≫ pullback.fst f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.fst f (𝒰.f i)) (𝒰.f i) ⋯ ⋯)
        (𝟙 X) (𝟙 ((diagonalCover f 𝒰 𝒱).X ⟨i, (j, j)⟩)) (𝟙 (pullback.diagonalObj f)) ⋯ ⋯ ≫
      (pullbackDiagonalMapIso f (𝒰.f i) ((𝒱 i).f j) ((𝒱 i).f j)).hom =
    (pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
        pullback.snd ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i))) ≫
      pullback.diagonal ((𝒱 i).f j)

Tactic:
apply pullback.hom_ext

Goal state after:
case h₁.h₀
X Y Z : Scheme
𝒰✝ : X.OpenCover
f✝ : X ⟶ Z
g : Y ⟶ Z
inst✝ : ∀ (i : 𝒰✝.I₀), HasPullback (𝒰✝.f i ≫ f✝) g
s : PullbackCone f✝ g
f : X ⟶ Y
𝒰 : Y.OpenCover
𝒱 : (i : (Precoverage.ZeroHypercover.pullback₁ f 𝒰).I₀) → ((Precoverage.ZeroHypercover.pullback₁ f 𝒰).X i).OpenCover
i : (openCoverOfBase 𝒰 f f).I₀
j : (𝒱 i).I₀
H :
  pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
      pullback.snd ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) =
    pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
      pullback.fst ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i))
⊢ (pullback.map (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) (pullback.diagonal f)
          (pullback.map ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) f f
            ((𝒱 i).f j ≫ pullback.fst f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.fst f (𝒰.f i)) (𝒰.f i) ⋯ ⋯)
          (𝟙 X) (𝟙 ((diagonalCover f 𝒰 𝒱).X ⟨i, (j, j)⟩)) (𝟙 (pullback.diagonalObj f)) ⋯ ⋯ ≫
        (pullbackDiagonalMapIso f (𝒰.f i) ((𝒱 i).f j) ((𝒱 i).f j)).hom) ≫
      pullback.fst ((𝒱 i).f j) ((𝒱 i).f j) =
    ((pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
          pullback.snd ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i))) ≫
        pullback.diagonal ((𝒱 i).f j)) ≫
      pullback.fst ((𝒱 i).f j) ((𝒱 i).f j)

case h₁
X Y Z : Scheme
𝒰✝ : X.OpenCover
f✝ : X ⟶ Z
g : Y ⟶ Z
inst✝ : ∀ (i : 𝒰✝.I₀), HasPullback (𝒰✝.f i ≫ f✝) g
s : PullbackCone f✝ g
f : X ⟶ Y
𝒰 : Y.OpenCover
𝒱 : (i : (Precoverage.ZeroHypercover.pullback₁ f 𝒰).I₀) → ((Precoverage.ZeroHypercover.pullback₁ f 𝒰).X i).OpenCover
i : (openCoverOfBase 𝒰 f f).I₀
j : (𝒱 i).I₀
H :
  pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
      pullback.snd ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) =
    pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
      pullback.fst ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i))
⊢ (pullback.map (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) (pullback.diagonal f)
          (pullback.map ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) f f
            ((𝒱 i).f j ≫ pullback.fst f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.fst f (𝒰.f i)) (𝒰.f i) ⋯ ⋯)
          (𝟙 X) (𝟙 ((diagonalCover f 𝒰 𝒱).X ⟨i, (j, j)⟩)) (𝟙 (pullback.diagonalObj f)) ⋯ ⋯ ≫
        (pullbackDiagonalMapIso f (𝒰.f i) ((𝒱 i).f j) ((𝒱 i).f j)).hom) ≫
      pullback.snd ((𝒱 i).f j) ((𝒱 i).f j) =
    ((pullback.snd (pullback.diagonal f) ((diagonalCover f 𝒰 𝒱).f ⟨i, (j, j)⟩) ≫
          pullback.snd ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i)) ((𝒱 i).f j ≫ pullback.snd f (𝒰.f i))) ≫
        pullback.diagonal ((𝒱 i).f j)) ≫
      pullback.snd ((𝒱 i).f j) ((𝒱 i).f j)