-- Lean 4 proof step from Mathlib.CategoryTheory.Enriched.FunctorCategory (goal)
Goal:
V : Type u₁
inst : Category.{v₁, u₁} V
inst_1 : MonoidalCategory.{v₁, u₁} V
C : Type u₂
inst_2 : Category.{v₂, u₂} C
J : Type u₃
inst_3 : Category.{v₃, u₃} J
K : Type u₄
inst_4 : Category.{v₄, u₄} K
inst_5 : EnrichedOrdinaryCategory.{v₁, v₂, u₂, u₁} V C
F₁ F₂ F₃ F₄ : Functor.{v₃, v₂, u₃, u₂} J C
inst_6 : HasEnrichedHom.{v₁, v₂, v₃, u₁, u₂, u₃} V F₁ F₂
inst_7 : HasEnrichedHom.{v₁, v₂, v₃, u₁, u₂, u₃} V F₂ F₃
inst_8 : HasEnrichedHom.{v₁, v₂, v₃, u₁, u₂, u₃} V F₁ F₃
i j : J
f : i ⟶ j
this :
  Eq.{v₁ + 1} (α :=
    end_.{v₃, v₁, u₃, u₁} (diagram V F₂ F₃) ⟶ obj.{v₃, v₁, u₃, u₁} (obj (diagram V F₂ F₃) (Opposite.op i)) j)
    (end_.π (diagram V F₂ F₃) i ≫ map (obj (diagram V F₂ F₃) (Opposite.op i)) f)
    (end_.π (diagram V F₂ F₃) j ≫ NatTrans.app (map (diagram V F₂ F₃) f.op) j)
⊢ Eq.{v₁ + 1} (α :=
    tensorObj.{v₁, u₁} (𝒞 := inst) (enrichedHom.{v₁, v₂, v₃, u₁, u₂, u₃} V F₁ F₂)
        (enrichedHom.{v₁, v₂, v₃, u₁, u₂, u₃} V F₂ F₃) ⟶
      @EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₃.obj j))
    (((end_.π (diagram V F₁ F₂) i ⊗ₘ end_.π (diagram V F₂ F₃) i) ≫ eComp V (F₁.obj i) (F₂.obj i) (F₃.obj i)) ≫
      eHomWhiskerLeft V (F₁.obj i) (F₃.map f))
    ((end_.π (diagram V F₁ F₂) i ⊗ₘ end_.π (diagram V F₂ F₃) j) ≫
      Iso.inv (ρ_ (obj.{v₃, v₁, u₃, u₁} (obj (diagram V F₁ F₂) (Opposite.op i)) i)) ▷
          obj.{v₃, v₁, u₃, u₁} (obj (diagram V F₂ F₃) (Opposite.op j)) j ≫
        (obj.{v₃, v₁, u₃, u₁} (obj (diagram V F₁ F₂) (Opposite.op i)) i ◁
              (eHomEquiv V : (a : F₂.obj i ⟶ F₂.obj j) → 𝟙_ V ⟶ F₂.obj i ⟶[V] F₂.obj j) (F₂.map f)) ▷
            obj.{v₃, v₁, u₃, u₁} (obj (diagram V F₂ F₃) (Opposite.op j)) j ≫
          eComp V (Opposite.unop (F₁.op.obj (Opposite.op i))) (F₂.obj i) (F₂.obj j) ▷
              obj.{v₃, v₁, u₃, u₁} (obj (diagram V F₂ F₃) (Opposite.op j)) j ≫
            eComp V (Opposite.unop (F₁.op.obj (Opposite.op i))) (F₂.obj j) (F₃.obj j))
have dsimp : Eq.{v₁ + 1} (α :=
  tensorObj.{v₁, u₁} (𝒞 := inst) (enrichedHom.{v₁, v₂, v₃, u₁, u₂, u₃} V F₁ F₂)
      (enrichedHom.{v₁, v₂, v₃, u₁, u₂, u₃} V F₂ F₃) ⟶
    @EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₃.obj j))
  (CategoryStruct.comp (Y := @EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₃.obj i))
    ((end_.π (diagram V F₁ F₂) i ⊗ₘ end_.π (diagram V F₂ F₃) i) ≫ eComp V (F₁.obj i) (F₂.obj i) (F₃.obj i))
    (CategoryStruct.comp (Y :=
      tensorObj.{v₁, u₁} (𝒞 := inst) (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₃.obj i))
        (tensorUnit.{v₁, u₁} V (𝒞 := inst)))
      (Iso.inv (ρ_ (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₃.obj i))))
      (CategoryStruct.comp (Y :=
        tensorObj.{v₁, u₁} (𝒞 := inst) (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₃.obj i))
          (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₃.obj i) (F₃.obj j)))
        (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₃.obj i) ◁
          (eHomEquiv V : (a : F₃.obj i ⟶ F₃.obj j) → 𝟙_ V ⟶ F₃.obj i ⟶[V] F₃.obj j) (F₃.map f))
        (eComp V (F₁.obj i) (F₃.obj i) (F₃.obj j)))))
  ((end_.π (diagram V F₁ F₂) i ⊗ₘ end_.π (diagram V F₂ F₃) j) ≫
    CategoryStruct.comp (Y :=
      tensorObj.{v₁, u₁} (𝒞 := inst)
        (tensorObj.{v₁, u₁} (𝒞 := inst) (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₂.obj i))
          (tensorUnit.{v₁, u₁} V (𝒞 := inst)))
        (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₂.obj j) (F₃.obj j)))
      (Iso.inv (ρ_ (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₂.obj i))) ▷
        @EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₂.obj j) (F₃.obj j))
      (CategoryStruct.comp (Y :=
        tensorObj.{v₁, u₁} (𝒞 := inst)
          (tensorObj.{v₁, u₁} (𝒞 := inst) (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₂.obj i))
            (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₂.obj i) (F₂.obj j)))
          (@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₂.obj j) (F₃.obj j)))
        ((@EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₁.obj i) (F₂.obj i) ◁
            (eHomEquiv V : (a : F₂.obj i ⟶ F₂.obj j) → 𝟙_ V ⟶ F₂.obj i ⟶[V] F₂.obj j) (F₂.map f)) ▷
          @EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₂.obj j) (F₃.obj j))
        (eComp V (F₁.obj i) (F₂.obj i) (F₂.obj j) ▷
            @EnrichedCategory.Hom.{v₁, u₁, u₂} _ inst inst_1 _ _ (F₂.obj j) (F₃.obj j) ≫
          eComp V (F₁.obj i) (F₂.obj j) (F₃.obj j))))
Tactic: dsimp [eHomWhiskerLeft, eHomWhiskerRight] at this ⊢