-- Lean 4 proof step from Mathlib.CategoryTheory.Limits.Preserves.Presheaf (goal)
Goal:
C : Type u
inst : SmallCategory C
inst_1 : HasFiniteColimits C
A : Cᵒᵖ ⥤ Type u
J : Type
inst_2 : SmallCategory J
inst_3 : FinCategory J
K : J ⥤ Cᵒᵖ
inst_4 : IsFiltered.{u, u} (CostructuredArrow yoneda A)
⊢ Eq (α := A.obj (limit K) ⟶ limit (K ⋙ A))
    (CategoryStruct.comp (Y :=
      (colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)).obj (limit K))
      (Iso.hom
          (Iso.app
            ((Presheaf.isColimitTautologicalCocone A).coconePointUniqueUpToIso
              (colimit.isColimit (CostructuredArrow.proj yoneda A ⋙ yoneda)))
            (limit K)) :
        A.obj (limit K) ⟶
          (colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)).obj (limit K))
      (CategoryStruct.comp (Y :=
          colimit (J := CostructuredArrow yoneda A)
            ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)))
          (Iso.hom (colimitObjIsoColimitCompEvaluation (CostructuredArrow.proj yoneda A ⋙ yoneda) (limit K)) :
            (colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)).obj (limit K) ⟶
              colimit (J := CostructuredArrow yoneda A)
                ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)))
          (CategoryStruct.comp (Y :=
              colimit (J := CostructuredArrow yoneda A)
                (CostructuredArrow.proj yoneda A ⋙ yoneda ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)))
              (Iso.hom
                (HasColimit.isoOfNatIso
                  (associator (CostructuredArrow.proj yoneda A) yoneda (obj (evaluation Cᵒᵖ (Type u)) (limit K)))))
              (CategoryStruct.comp (Y :=
                colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ obj coyoneda (limit K)))
                (Iso.hom (HasColimit.isoOfNatIso (isoAux A K)) :
                  colimit (J := CostructuredArrow yoneda A)
                      (CostructuredArrow.proj yoneda A ⋙ yoneda ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)) ⟶
                    colimit (J := CostructuredArrow yoneda A)
                      (CostructuredArrow.proj yoneda A ⋙ obj coyoneda (limit K)))
                (CategoryStruct.comp (Y :=
                    colimit (J := CostructuredArrow yoneda A)
                      (limit
                        (K ⋙
                          coyoneda ⋙
                            obj (whiskeringLeft (CostructuredArrow yoneda A) C (Type u))
                              (CostructuredArrow.proj yoneda A))))
                    (Iso.hom
                      (HasColimit.isoOfNatIso
                        (preservesLimitIso
                          (coyoneda ⋙
                            obj (whiskeringLeft (CostructuredArrow yoneda A) C (Type u))
                              (CostructuredArrow.proj yoneda A))
                          K)))
                    (CategoryStruct.comp (Y := colimit (limit (functorToInterchange A K)))
                      (Iso.hom (HasColimit.isoOfNatIso (HasLimit.isoOfNatIso (functorToInterchangeIso A K).symm)) :
                        colimit (J := CostructuredArrow yoneda A)
                            (limit
                              (K ⋙
                                coyoneda ⋙
                                  obj (whiskeringLeft (CostructuredArrow yoneda A) C (Type u))
                                    (CostructuredArrow.proj yoneda A))) ⟶
                          colimit (limit (functorToInterchange A K)))
                      (CategoryStruct.comp (Y := limit (colimit (functorToInterchange A K).flip))
                          (Iso.hom (colimitLimitIso (functorToInterchange A K)) :
                            colimit (limit (functorToInterchange A K)) ⟶
                              limit (colimit (functorToInterchange A K).flip))
                          (CategoryStruct.comp (Y :=
                              limit
                                (colimit (J := CostructuredArrow yoneda A)
                                  ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (whiskeringLeft J Cᵒᵖ (Type u)) K)))
                              (Iso.hom (HasLimit.isoOfNatIso (HasColimit.isoOfNatIso (flipFunctorToInterchange A K))) :
                                limit (colimit (functorToInterchange A K).flip) ⟶
                                  limit
                                    (colimit (J := CostructuredArrow yoneda A)
                                      ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙
                                        obj (whiskeringLeft J Cᵒᵖ (Type u)) K)))
                              (CategoryStruct.comp (Y :=
                                  limit
                                    (K ⋙
                                      colimit (J := CostructuredArrow yoneda A)
                                        (CostructuredArrow.proj yoneda A ⋙ yoneda)))
                                  (Iso.hom
                                      (HasLimit.isoOfNatIso
                                        (colimitCompWhiskeringLeftIsoCompColimit
                                          (CostructuredArrow.proj yoneda A ⋙ yoneda) K)) :
                                    limit
                                        (colimit (J := CostructuredArrow yoneda A)
                                          ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙
                                            obj (whiskeringLeft J Cᵒᵖ (Type u)) K)) ⟶
                                      limit
                                        (K ⋙
                                          colimit (J := CostructuredArrow yoneda A)
                                            (CostructuredArrow.proj yoneda A ⋙ yoneda)))
                                  (Iso.hom
                                      (HasLimit.isoOfNatIso
                                        (K.isoWhiskerLeft
                                          (IsColimit.coconePointUniqueUpToIso
                                            (colimit.isColimit (CostructuredArrow.proj yoneda A ⋙ yoneda))
                                            (Presheaf.isColimitTautologicalCocone A)))) :
                                    limit
                                        (K ⋙
                                          colimit (J := CostructuredArrow yoneda A)
                                            (CostructuredArrow.proj yoneda A ⋙ yoneda)) ⟶
                                      limit (K ⋙ A)) :
                                limit
                                    (colimit (J := CostructuredArrow yoneda A)
                                      ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙
                                        obj (whiskeringLeft J Cᵒᵖ (Type u)) K)) ⟶
                                  limit (K ⋙ A)) :
                            limit (colimit (functorToInterchange A K).flip) ⟶ limit (K ⋙ A)) :
                        colimit (limit (functorToInterchange A K)) ⟶ limit (K ⋙ A))) :
                  colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ obj coyoneda (limit K)) ⟶
                    limit (K ⋙ A))) :
            colimit (J := CostructuredArrow yoneda A)
                ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)) ⟶
              limit (K ⋙ A)) :
        (colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)).obj (limit K) ⟶
          limit (K ⋙ A)))
    (limit.post K A)
have rw : Eq (α :=
  colimit (J := CostructuredArrow yoneda A)
      ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)) ⟶
    limit (K ⋙ A))
  (CategoryStruct.comp (Y :=
      (colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)).obj (limit K))
      (Iso.inv (colimitObjIsoColimitCompEvaluation (CostructuredArrow.proj yoneda A ⋙ yoneda) (limit K)) :
        colimit (J := CostructuredArrow yoneda A)
            ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)) ⟶
          (colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)).obj (limit K))
      (Iso.inv
            (Iso.app
              ((Presheaf.isColimitTautologicalCocone A).coconePointUniqueUpToIso
                (colimit.isColimit (CostructuredArrow.proj yoneda A ⋙ yoneda)))
              (limit K)) ≫
          limit.post K A :
        (colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)).obj (limit K) ⟶
          limit (K ⋙ A)) :
    colimit (J := CostructuredArrow yoneda A)
        ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)) ⟶
      limit (K ⋙ A))
  (CategoryStruct.comp (Y :=
      colimit (J := CostructuredArrow yoneda A)
        (CostructuredArrow.proj yoneda A ⋙ yoneda ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)))
      (Iso.hom
        (HasColimit.isoOfNatIso
          (associator (CostructuredArrow.proj yoneda A) yoneda (obj (evaluation Cᵒᵖ (Type u)) (limit K)))))
      (CategoryStruct.comp (Y :=
        colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ obj coyoneda (limit K)))
        (Iso.hom (HasColimit.isoOfNatIso (isoAux A K)) :
          colimit (J := CostructuredArrow yoneda A)
              (CostructuredArrow.proj yoneda A ⋙ yoneda ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)) ⟶
            colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ obj coyoneda (limit K)))
        (CategoryStruct.comp (Y :=
            colimit (J := CostructuredArrow yoneda A)
              (limit
                (K ⋙
                  coyoneda ⋙
                    obj (whiskeringLeft (CostructuredArrow yoneda A) C (Type u)) (CostructuredArrow.proj yoneda A))))
            (Iso.hom
              (HasColimit.isoOfNatIso
                (preservesLimitIso
                  (coyoneda ⋙
                    obj (whiskeringLeft (CostructuredArrow yoneda A) C (Type u)) (CostructuredArrow.proj yoneda A))
                  K)))
            (CategoryStruct.comp (Y := colimit (limit (functorToInterchange A K)))
              (Iso.hom (HasColimit.isoOfNatIso (HasLimit.isoOfNatIso (functorToInterchangeIso A K).symm)) :
                colimit (J := CostructuredArrow yoneda A)
                    (limit
                      (K ⋙
                        coyoneda ⋙
                          obj (whiskeringLeft (CostructuredArrow yoneda A) C (Type u))
                            (CostructuredArrow.proj yoneda A))) ⟶
                  colimit (limit (functorToInterchange A K)))
              (CategoryStruct.comp (Y := limit (colimit (functorToInterchange A K).flip))
                  (Iso.hom (colimitLimitIso (functorToInterchange A K)) :
                    colimit (limit (functorToInterchange A K)) ⟶ limit (colimit (functorToInterchange A K).flip))
                  (CategoryStruct.comp (Y :=
                      limit
                        (colimit (J := CostructuredArrow yoneda A)
                          ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (whiskeringLeft J Cᵒᵖ (Type u)) K)))
                      (Iso.hom (HasLimit.isoOfNatIso (HasColimit.isoOfNatIso (flipFunctorToInterchange A K))) :
                        limit (colimit (functorToInterchange A K).flip) ⟶
                          limit
                            (colimit (J := CostructuredArrow yoneda A)
                              ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (whiskeringLeft J Cᵒᵖ (Type u)) K)))
                      (CategoryStruct.comp (Y :=
                          limit
                            (K ⋙ colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)))
                          (Iso.hom
                              (HasLimit.isoOfNatIso
                                (colimitCompWhiskeringLeftIsoCompColimit (CostructuredArrow.proj yoneda A ⋙ yoneda)
                                  K)) :
                            limit
                                (colimit (J := CostructuredArrow yoneda A)
                                  ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙
                                    obj (whiskeringLeft J Cᵒᵖ (Type u)) K)) ⟶
                              limit
                                (K ⋙
                                  colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ yoneda)))
                          (Iso.hom
                              (HasLimit.isoOfNatIso
                                (K.isoWhiskerLeft
                                  (IsColimit.coconePointUniqueUpToIso
                                    (colimit.isColimit (CostructuredArrow.proj yoneda A ⋙ yoneda))
                                    (Presheaf.isColimitTautologicalCocone A)))) :
                            limit
                                (K ⋙
                                  colimit (J := CostructuredArrow yoneda A)
                                    (CostructuredArrow.proj yoneda A ⋙ yoneda)) ⟶
                              limit (K ⋙ A)) :
                        limit
                            (colimit (J := CostructuredArrow yoneda A)
                              ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (whiskeringLeft J Cᵒᵖ (Type u)) K)) ⟶
                          limit (K ⋙ A)) :
                    limit (colimit (functorToInterchange A K).flip) ⟶ limit (K ⋙ A)) :
                colimit (limit (functorToInterchange A K)) ⟶ limit (K ⋙ A))) :
          colimit (J := CostructuredArrow yoneda A) (CostructuredArrow.proj yoneda A ⋙ obj coyoneda (limit K)) ⟶
            limit (K ⋙ A))) :
    colimit (J := CostructuredArrow yoneda A)
        ((CostructuredArrow.proj yoneda A ⋙ yoneda) ⋙ obj (evaluation Cᵒᵖ (Type u)) (limit K)) ⟶
      limit (K ⋙ A))
Tactic: rw [Eq.comm, ← Iso.inv_comp_eq, ← Iso.inv_comp_eq]