-- Lean 4 proof step from Mathlib.AlgebraicGeometry.Sites.Representability (goal)
Goal:
F : Sheaf zariskiTopology (Type u)
ι : Type u
X : ι → Scheme
f : (i : ι) → Functor.obj yoneda (X i) ⟶ F.obj (P := Presheaf.IsSheaf zariskiTopology)
hf : ∀ (i : ι), IsOpenImmersion.presheaf (f i)
i_1 j_1 k : ι
i j : (glueData hf).J
⊢ Eq (α := Functor.obj yoneda ((glueData hf).V (i, j)) ⟶ F.obj (P := Presheaf.IsSheaf zariskiTopology))
    ((Equiv.symm yonedaEquiv :
          (a : F.obj.obj (op ((glueData hf).V (i, j)))) → yoneda.obj ((glueData hf).V (i, j)) ⟶ F.obj)
        ((ConcreteCategory.hom (FC := TypeCat.Fun)
                (F.obj (P := Presheaf.IsSheaf zariskiTopology).map ((glueData hf).f i j).op) :
              (a : (fun (X : Type u) ↦ X) (F.obj.obj (op ((glueData hf).U i)))) →
                (fun (X : Type u) ↦ X) (F.obj.obj (op ((glueData hf).V (i, j)))))
            ((fun (i : (glueData hf).J) ↦
                ((yonedaEquiv : (a : yoneda.obj ((glueData hf).U i) ⟶ F.obj) → F.obj.obj (op ((glueData hf).U i)))
                    (f i) :
                  F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op ((glueData hf).U i))))
              i) :
          (fun (X : Type u) ↦ X) (F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op ((glueData hf).V (i, j))))) :
      Functor.obj yoneda ((glueData hf).V (i, j)) ⟶ F.obj (P := Presheaf.IsSheaf zariskiTopology))
    ((Equiv.symm yonedaEquiv :
          (a : F.obj.obj (op ((glueData hf).V (i, j)))) → yoneda.obj ((glueData hf).V (i, j)) ⟶ F.obj)
        ((ConcreteCategory.hom (FC := TypeCat.Fun)
                (F.obj (P := Presheaf.IsSheaf zariskiTopology).map
                  (((glueData hf).f j i).op ≫ ((glueData hf).t i j).op)) :
              (a : (fun (X : Type u) ↦ X) (F.obj.obj (op ((glueData hf).U j)))) →
                (fun (X : Type u) ↦ X) (F.obj.obj (op ((glueData hf).V (i, j)))))
            ((fun (i : (glueData hf).J) ↦
                ((yonedaEquiv : (a : yoneda.obj ((glueData hf).U i) ⟶ F.obj) → F.obj.obj (op ((glueData hf).U i)))
                    (f i) :
                  F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op ((glueData hf).U i))))
              j) :
          (fun (X : Type u) ↦ X) (F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op ((glueData hf).V (i, j))))) :
      Functor.obj yoneda ((glueData hf).V (i, j)) ⟶ F.obj (P := Presheaf.IsSheaf zariskiTopology))
have a : Eq (α := Functor.obj yoneda (sorry.pullback (f j)) ⟶ F.obj (P := Presheaf.IsSheaf zariskiTopology))
  ((Equiv.symm yonedaEquiv : (a : F.obj.obj (op (sorry.pullback (f j)))) → yoneda.obj (sorry.pullback (f j)) ⟶ F.obj)
      ((ConcreteCategory.hom (FC := TypeCat.Fun) (F.obj (P := Presheaf.IsSheaf zariskiTopology).map (sorry.fst' (f j)).op) :
            (a : F.obj.obj (op (X i))) → F.obj.obj (op (sorry.pullback (f j))))
          ((yonedaEquiv : (a : yoneda.obj (X i) ⟶ F.obj) → F.obj.obj (op (X i))) (f i) :
            F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op (X i))) :
        F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op (sorry.pullback (f j)))) :
    Functor.obj yoneda (sorry.pullback (f j)) ⟶ F.obj (P := Presheaf.IsSheaf zariskiTopology))
  ((Equiv.symm yonedaEquiv : (a : F.obj.obj (op (sorry.pullback (f j)))) → yoneda.obj (sorry.pullback (f j)) ⟶ F.obj)
      ((ConcreteCategory.hom (FC := TypeCat.Fun)
              (F.obj (P := Presheaf.IsSheaf zariskiTopology).map ((sorry.fst' (f i)).op ≫ (sorry.symmetry sorry).op)) :
            (a : F.obj.obj (op (X j))) → F.obj.obj (op (sorry.pullback (f j))))
          ((yonedaEquiv : (a : yoneda.obj (X j) ⟶ F.obj) → F.obj.obj (op (X j))) (f j) :
            F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op (X j))) :
        F.obj (P := Presheaf.IsSheaf zariskiTopology).obj (op (sorry.pullback (f j)))) :
    Functor.obj yoneda (sorry.pullback (f j)) ⟶ F.obj (P := Presheaf.IsSheaf zariskiTopology))
Tactic: dsimp only [glueData_V, glueData_J, glueData_U, glueData_f, glueData_t]