-- Lean 4 proof step from Mathlib.AlgebraicGeometry.AffineTransitionLimit (goal)
Goal:
I : Type u
inst : Category.{u, u} I
D : I ⥤ Scheme
c : Cone D
hc : IsLimit c
inst_1 : IsCofiltered I
inst_2 : ∀ {i j : I} (f : i ⟶ j), IsAffineHom (D.map f)
s : (↑Γ(c.pt, ⊤) : Type u)
inst_3 : ∀ (i : I), CompactSpace.{u} ↥(D.obj i)
inst_4 : ∀ (i : I), QuasiSeparatedSpace.{u} ↥(D.obj i)
this : CompactSpace.{u} ↥c.pt
i : (x : ↥c.pt) → I
U : (x : ↥c.pt) → (D.obj (i x)).Opens
hU : ∀ (x : ↥c.pt), IsAffineOpen (U x)
hxU : ∀ (x : ↥c.pt), Membership.mem (α := ↥(D.obj (i x))) (U x) ((c.π.app (i x)) x : ↥(D.obj (i x)))
t : (x : ↥c.pt) → (↑Γ(D.obj (i x), U x) : Type u)
ht :
  ∀ (x : ↥c.pt),
    Eq (α := (↑Γ(c.pt, c.π.app (i x) ⁻¹ᵁ U x) : Type u))
      ((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u}) ↦ (↑R : Type u) →+* (↑S : Type u)) (CC :=
              CommRingCat.carrier) (Y := Γ(c.pt, c.π.app (i x) ⁻¹ᵁ U x)) (Scheme.Hom.app (c.π.app (i x)) (U x)) :
            (a : (↑Γ(D.obj (i x), U x) : Type u)) → (↑Γ(c.pt, c.π.app (i x) ⁻¹ᵁ U x) : Type u))
          (t x) :
        (↑Γ(c.pt, c.π.app (i x) ⁻¹ᵁ U x) : Type u))
      (TopCat.Presheaf.restrictOpen (FC := fun (R S : CommRingCat.{u}) ↦ (↑R : Type u) →+* (↑S : Type u)) (CC :=
          CommRingCat.carrier) s (c.π.app (i x) ⁻¹ᵁ U x) ⋯ :
        ToType (FC := fun (R S : CommRingCat.{u}) ↦ (↑R : Type u) →+* (↑S : Type u)) (CC := CommRingCat.carrier)
          (c.pt.presheaf.obj (Opposite.op (c.π.app (i x) ⁻¹ᵁ U x))))
x y : ↥c.pt
j : I
fjx : j ⟶ i x
fjy : j ⟶ i y
⊢ Eq (α := (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
    ((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u}) ↦ (↑R : Type u) →+* (↑S : Type u)) (CC :=
            CommRingCat.carrier) (Y := Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)))
            (Scheme.Hom.appLE (c.π.app (i x)) (U x) (c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) ⋯) :
          (a : (↑Γ(D.obj (i x), U x) : Type u)) →
            (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
        (t x) :
      (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
    ((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u}) ↦ (↑R : Type u) →+* (↑S : Type u)) (CC :=
            CommRingCat.carrier) (Y := Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)))
            (Scheme.Hom.appLE (c.π.app (i y)) (U y) (c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) ⋯) :
          (a : (↑Γ(D.obj (i y), U y) : Type u)) →
            (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
        (t y) :
      (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
have simp_rw : Eq (α := (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
  ((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u}) ↦ (↑R : Type u) →+* (↑S : Type u)) (CC :=
          CommRingCat.carrier) (X := c.pt.presheaf.obj (Opposite.op ⊤)) (Y :=
          Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)))
          (c.pt.presheaf.map
            (CategoryStruct.comp (Y := Opposite.op (c.π.app (i x) ⁻¹ᵁ U x)) (Quiver.Hom.op (homOfLE sorry))
              (Quiver.Hom.op (homOfLE sorry)))) :
        (a : (↑(c.pt.presheaf.obj (Opposite.op ⊤)) : Type u)) →
          (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
      s :
    (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
  ((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u}) ↦ (↑R : Type u) →+* (↑S : Type u)) (CC :=
          CommRingCat.carrier) (X := c.pt.presheaf.obj (Opposite.op ⊤)) (Y :=
          Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)))
          (c.pt.presheaf.map
            (CategoryStruct.comp (Y := Opposite.op (c.π.app (i y) ⁻¹ᵁ U y)) (Quiver.Hom.op (homOfLE sorry))
              (Quiver.Hom.op (homOfLE sorry)))) :
        (a : (↑(c.pt.presheaf.obj (Opposite.op ⊤)) : Type u)) →
          (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
      s :
    (↑Γ(c.pt, c.π.app j ⁻¹ᵁ (D.map fjx ⁻¹ᵁ U x ⊓ D.map fjy ⁻¹ᵁ U y)) : Type u))
Tactic: simp_rw [Scheme.Hom.appLE, ConcreteCategory.comp_apply, ht, TopCat.Presheaf.restrictOpen,
        TopCat.Presheaf.restrict, ← ConcreteCategory.comp_apply, ← Functor.map_comp]