-- Mathlib/CategoryTheory/Triangulated/Pretriangulated.lean
lemma exists_iso_of_arrow_iso (T₁ T₂ : Triangle C) (hT₁ : T₁ ∈ distTriang C)
    (hT₂ : T₂ ∈ distTriang C) (e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁) :
    ∃ (e' : T₁ ≅ T₂), e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
⊢ ∃ e', e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Tactic:
have : IsIso φ.hom₁ := by dsimp [φ]; infer_instance

Result:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this : IsIso φ.hom₁
⊢ ∃ e', e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this : IsIso φ.hom₁
⊢ IsIso φ.hom₂

Tactic:
dsimp [φ]

Result:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this : IsIso φ.hom₁
⊢ IsIso e.hom.right

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this : IsIso φ.hom₁
⊢ ∃ e', e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Tactic:
have : IsIso φ.hom₂ := by dsimp [φ]; infer_instance

Result:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this✝ : IsIso φ.hom₁
this : IsIso φ.hom₂
⊢ ∃ e', e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this✝¹ : IsIso φ.hom₁
this✝ : IsIso φ.hom₂
this : IsIso φ.hom₃
⊢ ∃ e', e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Tactic:
have : IsIso φ := by
  apply Triangle.isIso_of_isIsos
  all_goals infer_instance

Result:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this✝² : IsIso φ.hom₁
this✝¹ : IsIso φ.hom₂
this✝ : IsIso φ.hom₃
this : IsIso φ
⊢ ∃ e', e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this✝² : IsIso φ.hom₁
this✝¹ : IsIso φ.hom₂
this✝ : IsIso φ.hom₃
this : IsIso φ
⊢ ∃ e', e'.hom.hom₁ = e.hom.left ∧ e'.hom.hom₂ = e.hom.right

Tactic:
exact ⟨asIso φ, by simp [φ], by simp [φ]⟩

Result:
no goals

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this : IsIso φ.hom₁
⊢ IsIso e.hom.right

Tactic:
infer_instance

Result:
no goals

Proof state:
case h₃
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this✝¹ : IsIso φ.hom₁
this✝ : IsIso φ.hom₂
this : IsIso φ.hom₃
⊢ IsIso φ.hom₃

Tactic:
infer_instance

Result:
no goals

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
T₁ T₂ : Triangle C
hT₁ : T₁ ∈ distinguishedTriangles
hT₂ : T₂ ∈ distinguishedTriangles
e : Arrow.mk T₁.mor₁ ≅ Arrow.mk T₂.mor₁
φ : T₁ ⟶ T₂ := completeDistinguishedTriangleMorphism T₁ T₂ hT₁ hT₂ e.hom.left e.hom.right ⋯
this✝² : IsIso φ.hom₁
this✝¹ : IsIso φ.hom₂
this✝ : IsIso φ.hom₃
this : IsIso φ
⊢ (asIso φ).hom.hom₁ = e.hom.left

Tactic:
simp [φ]

Result:
no goals