-- Lean 4 proof step from Mathlib.CategoryTheory.Triangulated.Opposite.Functor (goal)
Goal:
C : Type u_1
D : Type u_2
inst : Category.{v_1, u_1} C
inst_1 : Category.{v_2, u_2} D
inst_2 : HasShift.{v_1, u_1, 0} C ℤ
inst_3 : HasShift.{v_2, u_2, 0} D ℤ
F : Functor.{v_1, v_2, u_1, u_2} C D
inst_4 : F.CommShift ℤ
X : Cᵒᵖ
n : ℤ
⊢ Eq (α := F.obj (unop (obj.{v_1, v_1, u_1, u_1} (𝟭 Cᵒᵖ) X)) ⟶ F.obj (unop (obj.{v_1, v_1, u_1, u_1} (𝟭 Cᵒᵖ) X)))
    (F.map (Quiver.Hom.unop (𝟙 (obj.{v_1, v_1, u_1, u_1} (𝟭 Cᵒᵖ) X))))
    (CategoryStruct.comp (Y :=
      F.obj
        (unop
          (obj.{v_1, v_1, u_1, u_1}
            (Equivalence.inverse (opShiftFunctorEquivalence C n) ⋙ Equivalence.functor (opShiftFunctorEquivalence C n))
            X)))
      (CategoryStruct.comp (Y :=
          unop
            (obj.{v_2, v_2, u_2, u_2}
              (Equivalence.inverse (opShiftFunctorEquivalence D n) ⋙
                Equivalence.functor (opShiftFunctorEquivalence D n))
              (op (F.obj (unop X)))))
          (Quiver.Hom.unop
            (NatTrans.app (Iso.hom (Equivalence.counitIso (opShiftFunctorEquivalence D n))) (op (F.obj (unop X)))))
          (CategoryStruct.comp (Y :=
            unop (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n) (op ((shiftFunctor C n ⋙ F).obj (unop X)))))
            (Quiver.Hom.unop
                (map (shiftFunctor Dᵒᵖ n) (Quiver.Hom.op (NatTrans.app (Iso.inv (commShiftIso F n)) (unop X)))) :
              unop (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n) (op ((F ⋙ shiftFunctor D n).obj (unop X)))) ⟶
                unop (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n) (op ((shiftFunctor C n ⋙ F).obj (unop X)))))
            (Quiver.Hom.unop
                (NatTrans.app (Iso.hom (commShiftIso F.op n))
                  (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))) :
              unop ((F.op ⋙ shiftFunctor Dᵒᵖ n).obj (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))) ⟶
                unop ((shiftFunctor Cᵒᵖ n ⋙ F.op).obj (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))))) :
        unop (obj.{v_2, v_2, u_2, u_2} (𝟭 Dᵒᵖ) (op (F.obj (unop X)))) ⟶
          unop ((shiftFunctor Cᵒᵖ n ⋙ F.op).obj (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))))
      (CategoryStruct.comp (Y :=
        unop ((F.op ⋙ shiftFunctor Dᵒᵖ n).obj (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))))
        (Quiver.Hom.unop
          (NatTrans.app (Iso.inv (commShiftIso F.op n)) (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))))
        (CategoryStruct.comp (Y :=
          unop (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n) (op ((F ⋙ shiftFunctor D n).obj (unop X)))))
          (Quiver.Hom.unop
              (map (shiftFunctor Dᵒᵖ n) (Quiver.Hom.op (NatTrans.app (Iso.hom (commShiftIso F n)) (unop X)))) :
            unop (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n) (op ((shiftFunctor C n ⋙ F).obj (unop X)))) ⟶
              unop (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n) (op ((F ⋙ shiftFunctor D n).obj (unop X)))))
          (Quiver.Hom.unop
              (NatTrans.app (Iso.inv (Equivalence.counitIso (opShiftFunctorEquivalence D n))) (op (F.obj (unop X)))) :
            unop
                (obj.{v_2, v_2, u_2, u_2}
                  (Equivalence.inverse (opShiftFunctorEquivalence D n) ⋙
                    Equivalence.functor (opShiftFunctorEquivalence D n))
                  (op (F.obj (unop X)))) ⟶
              unop (obj.{v_2, v_2, u_2, u_2} (𝟭 Dᵒᵖ) (op (F.obj (unop X))))))))
have dsimp : F.map (𝟙 (unop X)) =
  CategoryStruct.comp (Y :=
    F.obj
      (unop
        (obj.{v_1, v_1, u_1, u_1} (shiftFunctor Cᵒᵖ n) (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))))
    (CategoryStruct.comp (Y :=
      unop
        (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
          (op (obj.{v_2, v_2, u_2, u_2} (shiftFunctor D n) (F.obj (unop X))))))
      (Quiver.Hom.unop
          (NatTrans.app (Iso.hom (Equivalence.counitIso (opShiftFunctorEquivalence D n))) (op (F.obj (unop X)))) :
        unop (op (F.obj (unop X))) ⟶
          unop
            (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
              (op (obj.{v_2, v_2, u_2, u_2} (shiftFunctor D n) (F.obj (unop X))))))
      (CategoryStruct.comp (Y :=
          unop
            (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
              (op (F.obj (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))))
          (Quiver.Hom.unop
              (map (shiftFunctor Dᵒᵖ n) (Quiver.Hom.op (NatTrans.app (Iso.inv (commShiftIso F n)) (unop X)))) :
            unop
                (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
                  (op (obj.{v_2, v_2, u_2, u_2} (shiftFunctor D n) (F.obj (unop X))))) ⟶
              unop
                (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
                  (op (F.obj (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))))
          (Quiver.Hom.unop
              (NatTrans.app (Iso.hom (commShiftIso F.op n))
                (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))) :
            unop
                (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
                  (op (F.obj (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))) ⟶
              unop
                (op
                  (F.obj
                    (unop
                      (obj.{v_1, v_1, u_1, u_1} (shiftFunctor Cᵒᵖ n)
                        (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))))))) :
        unop
            (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
              (op (obj.{v_2, v_2, u_2, u_2} (shiftFunctor D n) (F.obj (unop X))))) ⟶
          F.obj
            (unop
              (obj.{v_1, v_1, u_1, u_1} (shiftFunctor Cᵒᵖ n)
                (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))))))
    (CategoryStruct.comp (Y :=
      unop
        (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
          (op (F.obj (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))))
      (Quiver.Hom.unop
          (NatTrans.app (Iso.inv (commShiftIso F.op n)) (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X)))) :
        unop
            (op
              (F.obj
                (unop
                  (obj.{v_1, v_1, u_1, u_1} (shiftFunctor Cᵒᵖ n)
                    (op (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))))) ⟶
          unop
            (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
              (op (F.obj (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))))
      (CategoryStruct.comp (Y :=
        unop
          (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
            (op (obj.{v_2, v_2, u_2, u_2} (shiftFunctor D n) (F.obj (unop X))))))
        (Quiver.Hom.unop
            (map (shiftFunctor Dᵒᵖ n) (Quiver.Hom.op (NatTrans.app (Iso.hom (commShiftIso F n)) (unop X)))) :
          unop
              (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
                (op (F.obj (obj.{v_1, v_1, u_1, u_1} (shiftFunctor C n) (unop X))))) ⟶
            unop
              (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
                (op (obj.{v_2, v_2, u_2, u_2} (shiftFunctor D n) (F.obj (unop X))))))
        (Quiver.Hom.unop
            (NatTrans.app (Iso.inv (Equivalence.counitIso (opShiftFunctorEquivalence D n))) (op (F.obj (unop X)))) :
          unop
              (obj.{v_2, v_2, u_2, u_2} (shiftFunctor Dᵒᵖ n)
                (op (obj.{v_2, v_2, u_2, u_2} (shiftFunctor D n) (F.obj (unop X))))) ⟶
            unop (op (F.obj (unop X))))))
Tactic: dsimp