Module: Mathlib.AlgebraicGeometry.AffineTransitionLimit

Goal state before:
pp: I : Type u
inst✝⁴ : Category.{u, u} I
D : I ⥤ Scheme
c : Cone D
hc : IsLimit c
inst✝³ : IsCofiltered I
inst✝² : ∀ {i j : I} (f : i ⟶ j), IsAffineHom (D.map f)
s : ↑Γ(c.pt, ⊤)
inst✝¹ : ∀ (i : I), CompactSpace ↥(D.obj i)
inst✝ : ∀ (i : I), QuasiSeparatedSpace ↥(D.obj i)
this : CompactSpace ↥c.pt
i : ↥c.pt → I
U : (x : ↥c.pt) → (D.obj (i x)).Opens
hU : ∀ (x : ↥c.pt), IsAffineOpen (U x)
hxU : ∀ (x : ↥c.pt), (c.π.app (i x)) x ∈ U x
t : (x : ↥c.pt) → ↑Γ(D.obj (i x), U x)
ht : ∀ (x : ↥c.pt), (ConcreteCategory.hom (Scheme.Hom.app (c.π.app (i x)) (U x))) (t x) = (s |_ c.π.app (i x) ⁻¹ᵁ U x) ⋯
j : ↥c.pt → ↥c.pt → I
fjx : (x y : ↥c.pt) → j x y ⟶ i x
fjy : (x y : ↥c.pt) → j x y ⟶ i y
hj :
  ∀ (x y : ↥c.pt),
    ((ConcreteCategory.hom (Scheme.Hom.app (D.map (fjx x y)) (U x))) (t x) |_
          (D.map (fjx x y) ⁻¹ᵁ U x ⊓ D.map (fjy x y) ⁻¹ᵁ U y))
        ⋯ =
      ((ConcreteCategory.hom (Scheme.Hom.app (D.map (fjy x y)) (U y))) (t y) |_
          (D.map (fjx x y) ⁻¹ᵁ U x ⊓ D.map (fjy x y) ⁻¹ᵁ U y))
        ⋯
σ : Finset ↥c.pt
hσ : ⋃ x ∈ σ, (c.π.app (i x) ⁻¹ᵁ U x).carrier = ⊤
σi : ↥c.pt → ↥c.pt
hσiσ : ∀ (x : ↥c.pt), σi x ∈ σ
hσi : ∀ (x : ↥c.pt), x ∈ (c.π.app (i (σi x)) ⁻¹ᵁ U (σi x)).carrier
S : Finset I := Finset.image i σ ∪ Finset.image₂ j σ σ
hiS : ∀ {x : ↥c.pt}, x ∈ σ → i x ∈ S
hjS : ∀ {x y : ↥c.pt}, x ∈ σ → y ∈ σ → j x y ∈ S
⊢ ∃ i t, s = (ConcreteCategory.hom (Scheme.Hom.appTop (c.π.app i))) t

Tactic:
obtain ⟨k, fk, hk⟩ := IsCofiltered.inf_exists S
    (σ.attach.image₂ (fun (x y : σ) ↦ ⟨j x.1 y.1, i x.1, hjS x.2 y.2, hiS x.2, fjx x y⟩) σ.attach ∪
    σ.attach.image₂ (fun (x y : σ) ↦ ⟨j x.1 y.1, i y.1, hjS x.2 y.2, hiS y.2, fjy x y⟩) σ.attach)

Goal state after:
I : Type u
inst✝⁴ : Category.{u, u} I
D : I ⥤ Scheme
c : Cone D
hc : IsLimit c
inst✝³ : IsCofiltered I
inst✝² : ∀ {i j : I} (f : i ⟶ j), IsAffineHom (D.map f)
s : ↑Γ(c.pt, ⊤)
inst✝¹ : ∀ (i : I), CompactSpace ↥(D.obj i)
inst✝ : ∀ (i : I), QuasiSeparatedSpace ↥(D.obj i)
this : CompactSpace ↥c.pt
i : ↥c.pt → I
U : (x : ↥c.pt) → (D.obj (i x)).Opens
hU : ∀ (x : ↥c.pt), IsAffineOpen (U x)
hxU : ∀ (x : ↥c.pt), (c.π.app (i x)) x ∈ U x
t : (x : ↥c.pt) → ↑Γ(D.obj (i x), U x)
ht : ∀ (x : ↥c.pt), (ConcreteCategory.hom (Scheme.Hom.app (c.π.app (i x)) (U x))) (t x) = (s |_ c.π.app (i x) ⁻¹ᵁ U x) ⋯
j : ↥c.pt → ↥c.pt → I
fjx : (x y : ↥c.pt) → j x y ⟶ i x
fjy : (x y : ↥c.pt) → j x y ⟶ i y
hj :
  ∀ (x y : ↥c.pt),
    ((ConcreteCategory.hom (Scheme.Hom.app (D.map (fjx x y)) (U x))) (t x) |_
          (D.map (fjx x y) ⁻¹ᵁ U x ⊓ D.map (fjy x y) ⁻¹ᵁ U y))
        ⋯ =
      ((ConcreteCategory.hom (Scheme.Hom.app (D.map (fjy x y)) (U y))) (t y) |_
          (D.map (fjx x y) ⁻¹ᵁ U x ⊓ D.map (fjy x y) ⁻¹ᵁ U y))
        ⋯
σ : Finset ↥c.pt
hσ : ⋃ x ∈ σ, (c.π.app (i x) ⁻¹ᵁ U x).carrier = ⊤
σi : ↥c.pt → ↥c.pt
hσiσ : ∀ (x : ↥c.pt), σi x ∈ σ
hσi : ∀ (x : ↥c.pt), x ∈ (c.π.app (i (σi x)) ⁻¹ᵁ U (σi x)).carrier
S : Finset I := Finset.image i σ ∪ Finset.image₂ j σ σ
hiS : ∀ {x : ↥c.pt}, x ∈ σ → i x ∈ S
hjS : ∀ {x y : ↥c.pt}, x ∈ σ → y ∈ σ → j x y ∈ S
k : I
fk : {X : I} → X ∈ S → (k ⟶ X)
hk :
  ∀ {X Y : I} (mX : X ∈ S) (mY : Y ∈ S) {f : X ⟶ Y},
    ⟨X, ⟨Y, ⟨mX, ⟨mY, f⟩⟩⟩⟩ ∈
        Finset.image₂ (fun x y ↦ ⟨j ↑x ↑y, ⟨i ↑x, ⟨⋯, ⟨⋯, fjx ↑x ↑y⟩⟩⟩⟩) σ.attach σ.attach ∪
          Finset.image₂ (fun x y ↦ ⟨j ↑x ↑y, ⟨i ↑y, ⟨⋯, ⟨⋯, fjy ↑x ↑y⟩⟩⟩⟩) σ.attach σ.attach →
      fk mX ≫ f = fk mY
⊢ ∃ i t, s = (ConcreteCategory.hom (Scheme.Hom.appTop (c.π.app i))) t