-- Mathlib/Algebra/Homology/BifunctorHomotopy.lean
lemma comm₁ (j : J) :
    (mapBifunctorMap f₁ f₂ F c).f j =
    (mapBifunctor K₁ K₂ F c).d j (c.next j) ≫
          mapBifunctorMapHomotopy.hom₁ h₁ f₂ F c (c.next j) j +
        mapBifunctorMapHomotopy.hom₁ h₁ f₂ F c j (c.prev j) ≫
          (mapBifunctor L₁ L₂ F c).d (c.prev j) j +
      (mapBifunctorMap f₁' f₂ F c).f j

Proof state:
C₁ : Type u_1
C₂ : Type u_2
D : Type u_3
I₁ : Type u_4
I₂ : Type u_5
J : Type u_6
inst✝¹¹ : Category.{u_8, u_1} C₁
inst✝¹⁰ : Category.{u_9, u_2} C₂
inst✝⁹ : Category.{u_7, u_3} D
inst✝⁸ : Preadditive C₁
inst✝⁷ : Preadditive C₂
inst✝⁶ : Preadditive D
c₁ : ComplexShape I₁
c₂ : ComplexShape I₂
K₁ L₁ : HomologicalComplex C₁ c₁
f₁ f₁' : K₁ ⟶ L₁
h₁ : Homotopy f₁ f₁'
K₂ L₂ : HomologicalComplex C₂ c₂
f₂ : K₂ ⟶ L₂
F : C₁ ⥤ C₂ ⥤ D
inst✝⁵ : F.Additive
inst✝⁴ : ∀ (X₁ : C₁), (F.obj X₁).Additive
c : ComplexShape J
inst✝³ : DecidableEq J
inst✝² : TotalComplexShape c₁ c₂ c
inst✝¹ : K₁.HasMapBifunctor K₂ F c
inst✝ : L₁.HasMapBifunctor L₂ F c
j : J
i₁ : I₁
i₂ : I₂
h : c₁.π c₂ c (i₁, i₂) = j
⊢ ∀ {X Y : D} (a b c d e f : X ⟶ Y), a = c → b = e → f = -d → a + b = c + d + (e + f)

Tactic:
rintro X Y a b _ d _ _ rfl rfl rfl

Result:
C₁ : Type u_1
C₂ : Type u_2
D : Type u_3
I₁ : Type u_4
I₂ : Type u_5
J : Type u_6
inst✝¹¹ : Category.{u_8, u_1} C₁
inst✝¹⁰ : Category.{u_9, u_2} C₂
inst✝⁹ : Category.{u_7, u_3} D
inst✝⁸ : Preadditive C₁
inst✝⁷ : Preadditive C₂
inst✝⁶ : Preadditive D
c₁ : ComplexShape I₁
c₂ : ComplexShape I₂
K₁ L₁ : HomologicalComplex C₁ c₁
f₁ f₁' : K₁ ⟶ L₁
h₁ : Homotopy f₁ f₁'
K₂ L₂ : HomologicalComplex C₂ c₂
f₂ : K₂ ⟶ L₂
F : C₁ ⥤ C₂ ⥤ D
inst✝⁵ : F.Additive
inst✝⁴ : ∀ (X₁ : C₁), (F.obj X₁).Additive
c : ComplexShape J
inst✝³ : DecidableEq J
inst✝² : TotalComplexShape c₁ c₂ c
inst✝¹ : K₁.HasMapBifunctor K₂ F c
inst✝ : L₁.HasMapBifunctor L₂ F c
j : J
i₁ : I₁
i₂ : I₂
h : c₁.π c₂ c (i₁, i₂) = j
X Y : D
a b d : X ⟶ Y
⊢ a + b = a + d + (b + -d)

Proof state:
case h.a
C₁ : Type u_1
C₂ : Type u_2
D : Type u_3
I₁ : Type u_4
I₂ : Type u_5
J : Type u_6
inst✝¹¹ : Category.{u_8, u_1} C₁
inst✝¹⁰ : Category.{u_9, u_2} C₂
inst✝⁹ : Category.{u_7, u_3} D
inst✝⁸ : Preadditive C₁
inst✝⁷ : Preadditive C₂
inst✝⁶ : Preadditive D
c₁ : ComplexShape I₁
c₂ : ComplexShape I₂
K₁ L₁ : HomologicalComplex C₁ c₁
f₁ f₁' : K₁ ⟶ L₁
h₁ : Homotopy f₁ f₁'
K₂ L₂ : HomologicalComplex C₂ c₂
f₂ : K₂ ⟶ L₂
F : C₁ ⥤ C₂ ⥤ D
inst✝⁵ : F.Additive
inst✝⁴ : ∀ (X₁ : C₁), (F.obj X₁).Additive
c : ComplexShape J
inst✝³ : DecidableEq J
inst✝² : TotalComplexShape c₁ c₂ c
inst✝¹ : K₁.HasMapBifunctor K₂ F c
inst✝ : L₁.HasMapBifunctor L₂ F c
j : J
i₁ : I₁
i₂ : I₂
h : c₁.π c₂ c (i₁, i₂) = j
this : ∀ {X Y : D} (a b c d e f : X ⟶ Y), a = c → b = e → f = -d → a + b = c + d + (e + f)
⊢ (F.map (h₁.hom i₁ (c₁.prev i₁))).app (K₂.X i₂) ≫
      (F.map (L₁.d (c₁.prev i₁) i₁)).app (K₂.X i₂) ≫
        (F.obj (L₁.X i₁)).map (f₂.f i₂) ≫ L₁.ιMapBifunctor L₂ F c i₁ i₂ j h =
    K₁.ιMapBifunctor K₂ F c i₁ i₂ j h ≫
      hom₁ h₁ f₂ F c j (c.prev j) ≫ (((F.mapBifunctorHomologicalComplex c₁ c₂).obj L₁).obj L₂).D₁ c (c.prev j) j

Tactic:
rw [ιMapBifunctor_hom₁_assoc _ _ _ _ _ _ _ _ _ _ rfl]

Result:
case h.a
C₁ : Type u_1
C₂ : Type u_2
D : Type u_3
I₁ : Type u_4
I₂ : Type u_5
J : Type u_6
inst✝¹¹ : Category.{u_8, u_1} C₁
inst✝¹⁰ : Category.{u_9, u_2} C₂
inst✝⁹ : Category.{u_7, u_3} D
inst✝⁸ : Preadditive C₁
inst✝⁷ : Preadditive C₂
inst✝⁶ : Preadditive D
c₁ : ComplexShape I₁
c₂ : ComplexShape I₂
K₁ L₁ : HomologicalComplex C₁ c₁
f₁ f₁' : K₁ ⟶ L₁
h₁ : Homotopy f₁ f₁'
K₂ L₂ : HomologicalComplex C₂ c₂
f₂ : K₂ ⟶ L₂
F : C₁ ⥤ C₂ ⥤ D
inst✝⁵ : F.Additive
inst✝⁴ : ∀ (X₁ : C₁), (F.obj X₁).Additive
c : ComplexShape J
inst✝³ : DecidableEq J
inst✝² : TotalComplexShape c₁ c₂ c
inst✝¹ : K₁.HasMapBifunctor K₂ F c
inst✝ : L₁.HasMapBifunctor L₂ F c
j : J
i₁ : I₁
i₂ : I₂
h : c₁.π c₂ c (i₁, i₂) = j
this : ∀ {X Y : D} (a b c d e f : X ⟶ Y), a = c → b = e → f = -d → a + b = c + d + (e + f)
⊢ (F.map (h₁.hom i₁ (c₁.prev i₁))).app (K₂.X i₂) ≫
      (F.map (L₁.d (c₁.prev i₁) i₁)).app (K₂.X i₂) ≫
        (F.obj (L₁.X i₁)).map (f₂.f i₂) ≫ L₁.ιMapBifunctor L₂ F c i₁ i₂ j h =
    (c₁.ε₁ c₂ c (c₁.prev i₁, i₂) •
        (F.map (h₁.hom i₁ (c₁.prev i₁))).app (K₂.X i₂) ≫
          (F.obj (L₁.X (c₁.prev i₁))).map (f₂.f i₂) ≫ L₁.ιMapBifunctorOrZero L₂ F c (c₁.prev i₁) i₂ (c.prev j)) ≫
      (((F.mapBifunctorHomologicalComplex c₁ c₂).obj L₁).obj L₂).D₁ c (c.prev j) j