-- Lean 4 proof step from Mathlib.AlgebraicGeometry.ProjectiveSpectrum.StructureSheaf (goal)
Goal:
A : Type u_1
σ : Type u_2
inst : CommRing A
inst_1 : SetLike σ A
inst_2 : AddSubgroupClass σ A
𝒜 : ℕ → σ
inst_3 : GradedRing 𝒜
x : (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)
U : Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)
hxU : x ∈ U
s :
  ToType (FC := fun (R S : CommRingCat.{u_1}) ↦ (↑R : Type u_1) →+* (↑S : Type u_1)) (CC := CommRingCat.carrier)
    (Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜)) (op U))
V : Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)
hxV :
  (↑(Subtype.mk (p := fun (x : (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)) ↦ x ∈ unop (op U)) x hxU) :
      (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)) ∈
    V
i : V ⟶ unop (op U)
n : ℕ
a b : ↥(𝒜 n)
h : ∀ (x : ↥V), (↑b : A) ∉ (↑x : (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)).asHomogeneousIdeal
e :
  ∀ (a_1 : (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)) (b_1 : a_1 ∈ V),
    (↑s : (x : ↥U) → at (↑x : (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)))
        (Subtype.mk (p := fun (x : (↑(ProjectiveSpectrum.top 𝒜) : Type u_1)) ↦ x ∈ U) a_1 ⋯) =
      HomogeneousLocalization.mk { deg := n, num := a, den := b, den_mem := ⋯ }
⊢ Eq (α := (↑(Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x) : Type u_1))
    (((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u_1}) ↦ (↑R : Type u_1) →+* (↑S : Type u_1)) (CC :=
              CommRingCat.carrier) (X :=
              Functor.obj (C := (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)
                (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                (op
                    (ProjectiveSpectrum.basicOpen 𝒜
                      (↑(HomogeneousLocalization.NumDenSameDeg.den { deg := n, num := a, den := b, den_mem := ⋯ }) :
                        A)) :
                  (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ))
              (Y := Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x)
              (Presheaf.germ (Sheaf.presheaf (Proj.structureSheaf 𝒜))
                  (ProjectiveSpectrum.basicOpen 𝒜
                    (↑(HomogeneousLocalization.NumDenSameDeg.den { deg := n, num := a, den := b, den_mem := ⋯ }) : A))
                  x ⋯ :
                Functor.obj (C := (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)
                    (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                    (op
                        (ProjectiveSpectrum.basicOpen 𝒜
                          (↑(HomogeneousLocalization.NumDenSameDeg.den
                                { deg := n, num := a, den := b, den_mem := ⋯ :
                                  HomogeneousLocalization.NumDenSameDeg 𝒜 x.asHomogeneousIdeal.toIdeal.primeCompl }) :
                            A)) :
                      (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ) ⟶
                  Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x) :
            (↑(Functor.obj (C := (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)
                    (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                    (op
                        (ProjectiveSpectrum.basicOpen 𝒜
                          (↑(HomogeneousLocalization.NumDenSameDeg.den { deg := n, num := a, den := b, den_mem := ⋯ }) :
                            A)) :
                      (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)) :
                Type u_1) →+*
              (↑(Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x) : Type u_1)) :
          (a :
              (↑((Proj.structureSheaf 𝒜).presheaf.obj
                    (op (ProjectiveSpectrum.basicOpen 𝒜 (↑{ deg := n, num := a, den := b, den_mem := ⋯ }.den : A)))) :
                Type u_1)) →
            (↑((Proj.structureSheaf 𝒜).presheaf.stalk x) : Type u_1))
        (sectionInBasicOpen 𝒜 x { deg := n, num := a, den := b, den_mem := ⋯ }) :
      (↑(Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x) : Type u_1))
    (((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u_1}) ↦ (↑R : Type u_1) →+* (↑S : Type u_1)) (CC :=
              CommRingCat.carrier) (X :=
              Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                (op U))
              (Y := Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x)
              (Presheaf.germ (Sheaf.presheaf (Proj.structureSheaf 𝒜)) U x hxU :
                Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                    (op U) ⟶
                  Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x) :
            (↑(Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                    (op U)) :
                Type u_1) →+*
              (↑(Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x) : Type u_1)) :
          (a : (↑((Proj.structureSheaf 𝒜).presheaf.obj (op U)) : Type u_1)) →
            (↑((Proj.structureSheaf 𝒜).presheaf.stalk x) : Type u_1))
        s :
      (↑(Presheaf.stalk (Sheaf.presheaf (Proj.structureSheaf 𝒜)) x) : Type u_1))
have refine : Eq (α :=
  (↑(Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜)) (op V)) :
    Type u_1))
  (((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u_1}) ↦ (↑R : Type u_1) →+* (↑S : Type u_1)) (CC :=
            CommRingCat.carrier) (X :=
            Functor.obj (C := (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)
              (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
              (op
                  (ProjectiveSpectrum.basicOpen 𝒜
                    (↑(HomogeneousLocalization.NumDenSameDeg.den { deg := n, num := a, den := b, den_mem := sorry }) : A)) :
                (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ))
            (Y :=
            Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
              (op V))
            (CategoryTheory.Functor.map (Sheaf.presheaf (Proj.structureSheaf 𝒜)) (Quiver.Hom.op (homOfLE sorry)) :
              Functor.obj (C := (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)
                  (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op
                      (ProjectiveSpectrum.basicOpen 𝒜
                        (↑(HomogeneousLocalization.NumDenSameDeg.den
                              { deg := n, num := a, den := b, den_mem := sorry :
                                HomogeneousLocalization.NumDenSameDeg 𝒜 x.asHomogeneousIdeal.toIdeal.primeCompl }) :
                          A)) :
                    (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ) ⟶
                Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op V)) :
          (↑(Functor.obj (C := (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)
                  (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op
                      (ProjectiveSpectrum.basicOpen 𝒜
                        (↑(HomogeneousLocalization.NumDenSameDeg.den { deg := n, num := a, den := b, den_mem := sorry }) :
                          A)) :
                    (Opens (↑(ProjectiveSpectrum.top 𝒜) : Type u_1))ᵒᵖ)) :
              Type u_1) →+*
            (↑(Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op V)) :
              Type u_1)) :
        (a :
            (↑((Proj.structureSheaf 𝒜).presheaf.obj
                  (op (ProjectiveSpectrum.basicOpen 𝒜 (↑{ deg := n, num := a, den := b, den_mem := sorry }.den : A)))) :
              Type u_1)) →
          (↑((Proj.structureSheaf 𝒜).presheaf.obj (op V)) : Type u_1))
      (sectionInBasicOpen 𝒜 x { deg := n, num := a, den := b, den_mem := sorry }) :
    (↑(Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜)) (op V)) :
      Type u_1))
  (((ConcreteCategory.hom (FC := fun (R S : CommRingCat.{u_1}) ↦ (↑R : Type u_1) →+* (↑S : Type u_1)) (CC :=
            CommRingCat.carrier) (X :=
            Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
              (op (unop (op U))))
            (Y :=
            Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
              (op V))
            (CategoryTheory.Functor.map (Sheaf.presheaf (Proj.structureSheaf 𝒜)) i.op :
              Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op (unop (op U))) ⟶
                Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op V)) :
          (↑(Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op (unop (op U)))) :
              Type u_1) →+*
            (↑(Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜))
                  (op V)) :
              Type u_1)) :
        (a : (↑((Proj.structureSheaf 𝒜).presheaf.obj (op (unop (op U)))) : Type u_1)) →
          (↑((Proj.structureSheaf 𝒜).presheaf.obj (op V)) : Type u_1))
      s :
    (↑(Functor.obj (Sheaf.presheaf (Proj.structureSheaf 𝒜) : Presheaf CommRingCat (ProjectiveSpectrum.top 𝒜)) (op V)) :
      Type u_1))
Tactic: refine Presheaf.germ_ext (C := CommRingCat) _ V hxV (homOfLE <| fun _ h' ↦ h ⟨_, h'⟩) i ?_