-- Mathlib/CategoryTheory/GradedObject/Monoidal.lean
@[reassoc]
lemma pentagon_inv :
    tensorHom (𝟙 X₁) (associator X₂ X₃ X₄).inv ≫ (associator X₁ (tensorObj X₂ X₃) X₄).inv ≫
        tensorHom (associator X₁ X₂ X₃).inv (𝟙 X₄) =
    (associator X₁ X₂ (tensorObj X₃ X₄)).inv ≫ (associator (tensorObj X₁ X₂) X₃ X₄).inv

Proof state:
case h.h
I : Type u
inst✝²⁵ : AddMonoid I
C : Type u_1
inst✝²⁴ : Category.{u_2, u_1} C
inst✝²³ : MonoidalCategory C
X₁ X₂ X₃ X₄ : GradedObject I C
inst✝²² : X₁.HasTensor X₂
inst✝²¹ : X₂.HasTensor X₃
inst✝²⁰ : X₃.HasTensor X₄
inst✝¹⁹ : (tensorObj X₁ X₂).HasTensor X₃
inst✝¹⁸ : X₁.HasTensor (tensorObj X₂ X₃)
inst✝¹⁷ : (tensorObj X₂ X₃).HasTensor X₄
inst✝¹⁶ : X₂.HasTensor (tensorObj X₃ X₄)
inst✝¹⁵ : (tensorObj (tensorObj X₁ X₂) X₃).HasTensor X₄
inst✝¹⁴ : (tensorObj X₁ (tensorObj X₂ X₃)).HasTensor X₄
inst✝¹³ : X₁.HasTensor (tensorObj (tensorObj X₂ X₃) X₄)
inst✝¹² : X₁.HasTensor (tensorObj X₂ (tensorObj X₃ X₄))
inst✝¹¹ : (tensorObj X₁ X₂).HasTensor (tensorObj X₃ X₄)
inst✝¹⁰ : X₁.HasGoodTensor₁₂Tensor X₂ X₃
inst✝⁹ : X₁.HasGoodTensorTensor₂₃ X₂ X₃
inst✝⁸ : X₁.HasGoodTensor₁₂Tensor (tensorObj X₂ X₃) X₄
inst✝⁷ : X₁.HasGoodTensorTensor₂₃ (tensorObj X₂ X₃) X₄
inst✝⁶ : X₂.HasGoodTensor₁₂Tensor X₃ X₄
inst✝⁵ : X₂.HasGoodTensorTensor₂₃ X₃ X₄
inst✝⁴ : (tensorObj X₁ X₂).HasGoodTensor₁₂Tensor X₃ X₄
inst✝³ : (tensorObj X₁ X₂).HasGoodTensorTensor₂₃ X₃ X₄
inst✝² : X₁.HasGoodTensor₁₂Tensor X₂ (tensorObj X₃ X₄)
inst✝¹ : X₁.HasGoodTensorTensor₂₃ X₂ (tensorObj X₃ X₄)
inst✝ : X₁.HasTensor₄ObjExt X₂ X₃ X₄
j i₁ i₂ i₃ i₄ : I
h : i₁ + i₂ + i₃ + i₄ = j
⊢ ιTensorObj₄ X₁ X₂ X₃ X₄ i₁ i₂ i₃ i₄ j h ≫
      (tensorHom (𝟙 X₁) (associator X₂ X₃ X₄).inv ≫
          (associator X₁ (tensorObj X₂ X₃) X₄).inv ≫ tensorHom (associator X₁ X₂ X₃).inv (𝟙 X₄))
        j =
    ιTensorObj₄ X₁ X₂ X₃ X₄ i₁ i₂ i₃ i₄ j h ≫
      ((associator X₁ X₂ (tensorObj X₃ X₄)).inv ≫ (associator (tensorObj X₁ X₂) X₃ X₄).inv) j

Tactic:
dsimp only [categoryOfGradedObjects_comp]

Result:
case h.h
I : Type u
inst✝²⁵ : AddMonoid I
C : Type u_1
inst✝²⁴ : Category.{u_2, u_1} C
inst✝²³ : MonoidalCategory C
X₁ X₂ X₃ X₄ : GradedObject I C
inst✝²² : X₁.HasTensor X₂
inst✝²¹ : X₂.HasTensor X₃
inst✝²⁰ : X₃.HasTensor X₄
inst✝¹⁹ : (tensorObj X₁ X₂).HasTensor X₃
inst✝¹⁸ : X₁.HasTensor (tensorObj X₂ X₃)
inst✝¹⁷ : (tensorObj X₂ X₃).HasTensor X₄
inst✝¹⁶ : X₂.HasTensor (tensorObj X₃ X₄)
inst✝¹⁵ : (tensorObj (tensorObj X₁ X₂) X₃).HasTensor X₄
inst✝¹⁴ : (tensorObj X₁ (tensorObj X₂ X₃)).HasTensor X₄
inst✝¹³ : X₁.HasTensor (tensorObj (tensorObj X₂ X₃) X₄)
inst✝¹² : X₁.HasTensor (tensorObj X₂ (tensorObj X₃ X₄))
inst✝¹¹ : (tensorObj X₁ X₂).HasTensor (tensorObj X₃ X₄)
inst✝¹⁰ : X₁.HasGoodTensor₁₂Tensor X₂ X₃
inst✝⁹ : X₁.HasGoodTensorTensor₂₃ X₂ X₃
inst✝⁸ : X₁.HasGoodTensor₁₂Tensor (tensorObj X₂ X₃) X₄
inst✝⁷ : X₁.HasGoodTensorTensor₂₃ (tensorObj X₂ X₃) X₄
inst✝⁶ : X₂.HasGoodTensor₁₂Tensor X₃ X₄
inst✝⁵ : X₂.HasGoodTensorTensor₂₃ X₃ X₄
inst✝⁴ : (tensorObj X₁ X₂).HasGoodTensor₁₂Tensor X₃ X₄
inst✝³ : (tensorObj X₁ X₂).HasGoodTensorTensor₂₃ X₃ X₄
inst✝² : X₁.HasGoodTensor₁₂Tensor X₂ (tensorObj X₃ X₄)
inst✝¹ : X₁.HasGoodTensorTensor₂₃ X₂ (tensorObj X₃ X₄)
inst✝ : X₁.HasTensor₄ObjExt X₂ X₃ X₄
j i₁ i₂ i₃ i₄ : I
h : i₁ + i₂ + i₃ + i₄ = j
⊢ ιTensorObj₄ X₁ X₂ X₃ X₄ i₁ i₂ i₃ i₄ j h ≫
      tensorHom (𝟙 X₁) (associator X₂ X₃ X₄).inv j ≫
        (associator X₁ (tensorObj X₂ X₃) X₄).inv j ≫ tensorHom (associator X₁ X₂ X₃).inv (𝟙 X₄) j =
    ιTensorObj₄ X₁ X₂ X₃ X₄ i₁ i₂ i₃ i₄ j h ≫
      (associator X₁ X₂ (tensorObj X₃ X₄)).inv j ≫ (associator (tensorObj X₁ X₂) X₃ X₄).inv j

Proof state:
I : Type u
inst✝²⁵ : AddMonoid I
C : Type u_1
inst✝²⁴ : Category.{u_2, u_1} C
inst✝²³ : MonoidalCategory C
X₁ X₂ X₃ X₄ : GradedObject I C
inst✝²² : X₁.HasTensor X₂
inst✝²¹ : X₂.HasTensor X₃
inst✝²⁰ : X₃.HasTensor X₄
inst✝¹⁹ : (tensorObj X₁ X₂).HasTensor X₃
inst✝¹⁸ : X₁.HasTensor (tensorObj X₂ X₃)
inst✝¹⁷ : (tensorObj X₂ X₃).HasTensor X₄
inst✝¹⁶ : X₂.HasTensor (tensorObj X₃ X₄)
inst✝¹⁵ : (tensorObj (tensorObj X₁ X₂) X₃).HasTensor X₄
inst✝¹⁴ : (tensorObj X₁ (tensorObj X₂ X₃)).HasTensor X₄
inst✝¹³ : X₁.HasTensor (tensorObj (tensorObj X₂ X₃) X₄)
inst✝¹² : X₁.HasTensor (tensorObj X₂ (tensorObj X₃ X₄))
inst✝¹¹ : (tensorObj X₁ X₂).HasTensor (tensorObj X₃ X₄)
inst✝¹⁰ : X₁.HasGoodTensor₁₂Tensor X₂ X₃
inst✝⁹ : X₁.HasGoodTensorTensor₂₃ X₂ X₃
inst✝⁸ : X₁.HasGoodTensor₁₂Tensor (tensorObj X₂ X₃) X₄
inst✝⁷ : X₁.HasGoodTensorTensor₂₃ (tensorObj X₂ X₃) X₄
inst✝⁶ : X₂.HasGoodTensor₁₂Tensor X₃ X₄
inst✝⁵ : X₂.HasGoodTensorTensor₂₃ X₃ X₄
inst✝⁴ : (tensorObj X₁ X₂).HasGoodTensor₁₂Tensor X₃ X₄
inst✝³ : (tensorObj X₁ X₂).HasGoodTensorTensor₂₃ X₃ X₄
inst✝² : X₁.HasGoodTensor₁₂Tensor X₂ (tensorObj X₃ X₄)
inst✝¹ : X₁.HasGoodTensorTensor₂₃ X₂ (tensorObj X₃ X₄)
inst✝ : X₁.HasTensor₄ObjExt X₂ X₃ X₄
j i₁ i₂ i₃ i₄ : I
h : i₁ + i₂ + i₃ + i₄ = j
⊢ i₁ + (i₂ + i₃) + i₄ = j

Tactic:
simp only [← add_assoc, h]

Result:
no goals

Proof state:
I : Type u
inst✝²⁵ : AddMonoid I
C : Type u_1
inst✝²⁴ : Category.{u_2, u_1} C
inst✝²³ : MonoidalCategory C
X₁ X₂ X₃ X₄ : GradedObject I C
inst✝²² : X₁.HasTensor X₂
inst✝²¹ : X₂.HasTensor X₃
inst✝²⁰ : X₃.HasTensor X₄
inst✝¹⁹ : (tensorObj X₁ X₂).HasTensor X₃
inst✝¹⁸ : X₁.HasTensor (tensorObj X₂ X₃)
inst✝¹⁷ : (tensorObj X₂ X₃).HasTensor X₄
inst✝¹⁶ : X₂.HasTensor (tensorObj X₃ X₄)
inst✝¹⁵ : (tensorObj (tensorObj X₁ X₂) X₃).HasTensor X₄
inst✝¹⁴ : (tensorObj X₁ (tensorObj X₂ X₃)).HasTensor X₄
inst✝¹³ : X₁.HasTensor (tensorObj (tensorObj X₂ X₃) X₄)
inst✝¹² : X₁.HasTensor (tensorObj X₂ (tensorObj X₃ X₄))
inst✝¹¹ : (tensorObj X₁ X₂).HasTensor (tensorObj X₃ X₄)
inst✝¹⁰ : X₁.HasGoodTensor₁₂Tensor X₂ X₃
inst✝⁹ : X₁.HasGoodTensorTensor₂₃ X₂ X₃
inst✝⁸ : X₁.HasGoodTensor₁₂Tensor (tensorObj X₂ X₃) X₄
inst✝⁷ : X₁.HasGoodTensorTensor₂₃ (tensorObj X₂ X₃) X₄
inst✝⁶ : X₂.HasGoodTensor₁₂Tensor X₃ X₄
inst✝⁵ : X₂.HasGoodTensorTensor₂₃ X₃ X₄
inst✝⁴ : (tensorObj X₁ X₂).HasGoodTensor₁₂Tensor X₃ X₄
inst✝³ : (tensorObj X₁ X₂).HasGoodTensorTensor₂₃ X₃ X₄
inst✝² : X₁.HasGoodTensor₁₂Tensor X₂ (tensorObj X₃ X₄)
inst✝¹ : X₁.HasGoodTensorTensor₂₃ X₂ (tensorObj X₃ X₄)
inst✝ : X₁.HasTensor₄ObjExt X₂ X₃ X₄
j i₁ i₂ i₃ i₄ : I
h : i₁ + i₂ + i₃ + i₄ = j
⊢ i₁ + i₂ + (i₃ + i₄) = j

Tactic:
rw [← add_assoc, h]

Result:
no goals