-- Lean 4 proof step from Mathlib.Geometry.RingedSpace.PresheafedSpace.HasColimits (goal)
Goal:
J : Type u'
inst : Category.{v', u'} J
C : Type u
inst_1 : Category.{v, u} C
inst_2 : HasColimitsOfShape.{v', u', v, v + 1} J TopCat
inst_3 : ∀ (X : TopCat.{v}), HasLimitsOfShape Jᵒᵖ (Presheaf C X)
inst_4 : HasLimitsOfShape.{v', u', v, u} Jᵒᵖ C
F : J ⥤ PresheafedSpace.{v, u, v} C
U : Opens (↑(↑(Limits.colimit F) : TopCat) : Type v)
j : J
⊢ Eq (α :=
    limit (componentwiseDiagram F U) ⟶ obj (obj (pushforward C (Hom.base (colimit.ι F j))) (F.obj j).presheaf) (op U))
    (CategoryStruct.comp (Y :=
          obj
            (obj
              (pushforward C
                (Hom.base
                  (Iso.hom
                    (Iso.symm
                      (colimit.isoColimitCocone
                        { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F })))))
              { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }.cocone.pt.presheaf)
            (op U))
          (CategoryStruct.comp (Y :=
            limit
              (Functor.comp (D :=
                CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                (Functor.leftOp (pushforwardDiagramToColimit F) :
                  Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
                (obj (evaluation (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                    (obj
                      (Functor.op
                        (Opens.map
                          (Hom.base
                            (Iso.hom
                              (Iso.symm
                                (colimit.isoColimitCocone
                                  { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                                    ColimitCocone F }))))))
                      (op U)) :
                  CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C ⥤ C)))
            (Iso.inv
                (mapIso lim (NatIso.ofComponents (fun (X : Jᵒᵖ) ↦ mapIso (F.obj (unop X)).presheaf (eqToIso ⋯)) ⋯)) :
              limit (componentwiseDiagram F U) ⟶
                limit
                  (Functor.comp (D :=
                    CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                    (Functor.leftOp (pushforwardDiagramToColimit F) :
                      Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
                    (obj (evaluation (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                        (obj
                          (Functor.op
                            (Opens.map
                              (Hom.base
                                (Iso.hom
                                  (Iso.symm
                                    (colimit.isoColimitCocone
                                      { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                                        ColimitCocone F }))))))
                          (op U)) :
                      CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C ⥤ C)))
            (Iso.inv
                (limitObjIsoLimitCompEvaluation (Functor.leftOp (pushforwardDiagramToColimit F))
                  (obj
                    (Functor.op
                      (Opens.map
                        (Hom.base
                          (Iso.hom
                            (Iso.symm
                              (colimit.isoColimitCocone
                                { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                                  ColimitCocone F }))))))
                    (op U))) :
              limit
                  (Functor.comp (D :=
                    CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                    (Functor.leftOp (pushforwardDiagramToColimit F) :
                      Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
                    (obj (evaluation (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                        (obj
                          (Functor.op
                            (Opens.map
                              (Hom.base
                                (Iso.hom
                                  (Iso.symm
                                    (colimit.isoColimitCocone
                                      { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                                        ColimitCocone F }))))))
                          (op U)) :
                      CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C ⥤
                        C)) ⟶
                obj
                  (obj
                    (pushforward C
                      (Hom.base
                        (Iso.hom
                          (Iso.symm
                            (colimit.isoColimitCocone
                              { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                                ColimitCocone F })))))
                    { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                            ColimitCocone F }.cocone.pt.presheaf)
                  (op U)))
          (CategoryStruct.comp (Y :=
            obj (C :=
              (Opens
                  (↑(obj (forget C)
                        { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                              ColimitCocone F }.cocone.pt) :
                    Type v))ᵒᵖ)
              (obj
                (pushforward C
                  (Iso.hom
                    (Iso.symm
                      (mapIso (forget C)
                        (Iso.symm
                          (colimit.isoColimitCocone
                            { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F }))))))
                (Limits.colimit F).presheaf)
              (op
                (obj
                  (Opens.map
                    (Iso.inv
                      (Iso.symm
                        (mapIso (forget C)
                          (Iso.symm
                            (colimit.isoColimitCocone
                              { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F }))))))
                  (unop (op U)))))
            (NatTrans.app
                (Hom.c
                  (Iso.hom
                    (colimit.isoColimitCocone { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F })))
                (op
                  (obj
                    (Opens.map
                      (Iso.inv
                        (Iso.symm
                          (mapIso (forget C)
                            (Iso.symm
                              (colimit.isoColimitCocone
                                { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F }))))))
                    (unop (op U)))) ≫
              (Limits.colimit F).presheaf.map (eqToHom ⋯))
            ((Limits.colimit F).presheaf.map (eqToHom ⋯))) ≫
        NatTrans.app (Hom.c (colimit.ι F j)) (op U) :
      limit (componentwiseDiagram F U) ⟶ obj (obj (pushforward C (Hom.base (colimit.ι F j))) (F.obj j).presheaf) (op U))
    (limit.π (componentwiseDiagram F U) (op j) :
      limit (componentwiseDiagram F U) ⟶ (componentwiseDiagram F U).obj (op j))
have dsimp : Eq (α := limit (componentwiseDiagram F U) ⟶ (F.obj j).presheaf.obj (op (obj (Opens.map (Hom.base (colimit.ι F j))) U)))
  (CategoryStruct.comp (Y :=
      obj
        (limit
            (Functor.leftOp (pushforwardDiagramToColimit F) :
              Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C))) :
          Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
        (op
          (obj
            (Opens.map
              (Hom.base
                (Iso.inv
                  (colimit.isoColimitCocone
                    { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
            U)))
      (CategoryStruct.comp (Y :=
          limit
            (Functor.comp (D :=
              CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
              (Functor.leftOp (pushforwardDiagramToColimit F) :
                Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
              (obj (evaluation (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                  (op
                    (obj
                      (Opens.map
                        (Hom.base
                          (Iso.inv
                            (colimit.isoColimitCocone
                              { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                      U)) :
                CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C ⥤ C)))
          (limMap (Iso.inv (NatIso.ofComponents (fun (X : Jᵒᵖ) ↦ mapIso (F.obj (unop X)).presheaf (eqToIso sorry)) sorry)) :
            limit (componentwiseDiagram F U) ⟶
              limit
                (Functor.comp (D :=
                  CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                  (Functor.leftOp (pushforwardDiagramToColimit F) :
                    Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
                  (obj (evaluation (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                      (op
                        (obj
                          (Opens.map
                            (Hom.base
                              (Iso.inv
                                (colimit.isoColimitCocone
                                  { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                                    ColimitCocone F }))))
                          U)) :
                    CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C ⥤ C)))
          (Iso.inv
              (limitObjIsoLimitCompEvaluation (Functor.leftOp (pushforwardDiagramToColimit F))
                (op
                  (obj
                    (Opens.map
                      (Hom.base
                        (Iso.inv
                          (colimit.isoColimitCocone
                            { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                    U))) :
            limit
                (Functor.comp (D :=
                  CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                  (Functor.leftOp (pushforwardDiagramToColimit F) :
                    Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
                  (obj (evaluation (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C)
                      (op
                        (obj
                          (Opens.map
                            (Hom.base
                              (Iso.inv
                                (colimit.isoColimitCocone
                                  { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F :
                                    ColimitCocone F }))))
                          U)) :
                    CategoryTheory.Functor.{v, v, v, u} (Opens (↑(Limits.colimit (F ⋙ forget C)) : Type v))ᵒᵖ C ⥤ C)) ⟶
              obj
                (limit
                    (Functor.leftOp (pushforwardDiagramToColimit F) :
                      Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C))) :
                  Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
                (op
                  (obj
                    (Opens.map
                      (Hom.base
                        (Iso.inv
                          (colimit.isoColimitCocone
                            { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                    U))) :
        limit (componentwiseDiagram F U) ⟶
          obj
            (limit
                (Functor.leftOp (pushforwardDiagramToColimit F) :
                  Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C))) :
              Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
            (op
              (obj
                (Opens.map
                  (Hom.base
                    (Iso.inv
                      (colimit.isoColimitCocone
                        { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                U)))
      (CategoryStruct.comp (Y :=
          (Limits.colimit F).presheaf.obj
            (op
              (obj
                (Opens.map
                  (Hom.base
                    (Iso.hom
                      (colimit.isoColimitCocone
                        { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                (obj
                  (Opens.map
                    (Hom.base
                      (Iso.inv
                        (colimit.isoColimitCocone
                          { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                  U))))
          (NatTrans.app
              (Hom.c
                (Iso.hom
                  (colimit.isoColimitCocone { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F })))
              (op
                (obj
                  (Opens.map
                    (Hom.base
                      (Iso.inv
                        (colimit.isoColimitCocone
                          { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                  U)) ≫
            (Limits.colimit F).presheaf.map
              (𝟙
                (op
                  (obj
                    (Opens.map
                      (Hom.base
                        (Iso.hom
                          (colimit.isoColimitCocone
                            { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                    (obj
                      (Opens.map
                        (Hom.base
                          (Iso.inv
                            (colimit.isoColimitCocone
                              { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                      U)))))
          ((Limits.colimit F).presheaf.map (eqToHom sorry)) :
        obj
            (limit
                (Functor.leftOp (pushforwardDiagramToColimit F) :
                  Jᵒᵖ ⥤ Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C))) :
              Presheaf.{v, v, u} C (Limits.colimit (F ⋙ forget C)))
            (op
              (obj
                (Opens.map
                  (Hom.base
                    (Iso.inv
                      (colimit.isoColimitCocone
                        { cocone := colimitCocone F, isColimit := colimitCoconeIsColimit F : ColimitCocone F }))))
                U)) ⟶
          (Limits.colimit F).presheaf.obj (op U)) ≫
    NatTrans.app (Hom.c (colimit.ι F j)) (op U))
  (limit.π (componentwiseDiagram F U) (op j))
Tactic: dsimp