Theorem: HomotopyCategory.Pretriangulated.contractible_distinguished
File: Mathlib/Algebra/Homology/HomotopyCategory/Pretriangulated.lean

Proof steps:
state_before: C : Type u_1
D : Type u_2
inst✝⁷ : Category.{u_3, u_1} C
inst✝⁶ : Category.{?u.432420, u_2} D
inst✝⁵ : Preadditive C
inst✝⁴ : HasZeroObject C
inst✝³ : HasBinaryBiproducts C
inst✝² : Preadditive D
inst✝¹ : HasZeroObject D
inst✝ : HasBinaryBiproducts D
K L : CochainComplex C ℤ
φ : K ⟶ L
X : HomotopyCategory C (ComplexShape.up ℤ)
⊢ contractibleTriangle X ∈ distinguishedTriangles C
state_after: case mk
C : Type u_1
D : Type u_2
inst✝⁷ : Category.{u_3, u_1} C
inst✝⁶ : Category.{?u.432420, u_2} D
inst✝⁵ : Preadditive C
inst✝⁴ : HasZeroObject C
inst✝³ : HasBinaryBiproducts C
inst✝² : Preadditive D
inst✝¹ : HasZeroObject D
inst✝ : HasBinaryBiproducts D
K L : CochainComplex C ℤ
φ : K ⟶ L
X : HomologicalComplex C (ComplexShape.up ℤ)
⊢ contractibleTriangle { as := X } ∈ distinguishedTriangles C
tactic: obtain ⟨X⟩ := X
state_before: case mk
C : Type u_1
D : Type u_2
inst✝⁷ : Category.{u_3, u_1} C
inst✝⁶ : Category.{?u.432420, u_2} D
inst✝⁵ : Preadditive C
inst✝⁴ : HasZeroObject C
inst✝³ : HasBinaryBiproducts C
inst✝² : Preadditive D
inst✝¹ : HasZeroObject D
inst✝ : HasBinaryBiproducts D
K L : CochainComplex C ℤ
φ : K ⟶ L
X : HomologicalComplex C (ComplexShape.up ℤ)
⊢ contractibleTriangle { as := X } ∈ distinguishedTriangles C
state_after: case mk
C : Type u_1
D : Type u_2
inst✝⁷ : Category.{u_3, u_1} C
inst✝⁶ : Category.{?u.432420, u_2} D
inst✝⁵ : Preadditive C
inst✝⁴ : HasZeroObject C
inst✝³ : HasBinaryBiproducts C
inst✝² : Preadditive D
inst✝¹ : HasZeroObject D
inst✝ : HasBinaryBiproducts D
K L : CochainComplex C ℤ
φ : K ⟶ L
X : HomologicalComplex C (ComplexShape.up ℤ)
⊢ contractibleTriangle { as := X } ≅ CochainComplex.mappingCone.triangleh (𝟙 X)
tactic: refine ⟨_, _, 𝟙 X, ⟨?_⟩⟩
state_before: case mk
C : Type u_1
D : Type u_2
inst✝⁷ : Category.{u_3, u_1} C
inst✝⁶ : Category.{?u.432420, u_2} D
inst✝⁵ : Preadditive C
inst✝⁴ : HasZeroObject C
inst✝³ : HasBinaryBiproducts C
inst✝² : Preadditive D
inst✝¹ : HasZeroObject D
inst✝ : HasBinaryBiproducts D
K L : CochainComplex C ℤ
φ : K ⟶ L
X : HomologicalComplex C (ComplexShape.up ℤ)
⊢ contractibleTriangle { as := X } ≅ CochainComplex.mappingCone.triangleh (𝟙 X)
state_after: case mk
C : Type u_1
D : Type u_2
inst✝⁷ : Category.{u_3, u_1} C
inst✝⁶ : Category.{?u.432420, u_2} D
inst✝⁵ : Preadditive C
inst✝⁴ : HasZeroObject C
inst✝³ : HasBinaryBiproducts C
inst✝² : Preadditive D
inst✝¹ : HasZeroObject D
inst✝ : HasBinaryBiproducts D
K L : CochainComplex C ℤ
φ : K ⟶ L
X : HomologicalComplex C (ComplexShape.up ℤ)
h : IsZero ((quotient C (ComplexShape.up ℤ)).obj (CochainComplex.mappingCone (𝟙 X)))
⊢ contractibleTriangle { as := X } ≅ CochainComplex.mappingCone.triangleh (𝟙 X)
tactic: have h := (isZero_quotient_obj_iff _).2 ⟨CochainComplex.mappingCone.homotopyToZeroOfId X⟩
state_before: case mk
C : Type u_1
D : Type u_2
inst✝⁷ : Category.{u_3, u_1} C
inst✝⁶ : Category.{?u.432420, u_2} D
inst✝⁵ : Preadditive C
inst✝⁴ : HasZeroObject C
inst✝³ : HasBinaryBiproducts C
inst✝² : Preadditive D
inst✝¹ : HasZeroObject D
inst✝ : HasBinaryBiproducts D
K L : CochainComplex C ℤ
φ : K ⟶ L
X : HomologicalComplex C (ComplexShape.up ℤ)
h : IsZero ((quotient C (ComplexShape.up ℤ)).obj (CochainComplex.mappingCone (𝟙 X)))
⊢ contractibleTriangle { as := X } ≅ CochainComplex.mappingCone.triangleh (𝟙 X)
state_after: no goals
tactic: exact Triangle.isoMk _ _ (Iso.refl _) (Iso.refl _) h.isoZero.symm
    (by simp) (h.eq_of_tgt _ _) (by dsimp; ext)