Theorem: CategoryTheory.Pretriangulated.exists_iso_binaryBiproduct_of_distTriang
File: Mathlib/CategoryTheory/Triangulated/Pretriangulated.lean

Proof steps:
state_before: 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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
state_after: 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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this : Epi T.mor₂
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
tactic: have := T.epi₂ hT zero
state_before: 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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this : Epi T.mor₂
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
state_after: 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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
tactic: have := isSplitEpi_of_epi T.mor₂
state_before: 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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
state_after: case intro
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
tactic: obtain ⟨fst, hfst⟩ := T.coyoneda_exact₂ hT (𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂) (by simp)
state_before: case intro
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
state_after: case intro
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
d : BinaryBiproductData T.obj₁ T.obj₃ := binaryBiproductData T hT zero (section_ T.mor₂) ⋯ fst ⋯
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
tactic: let d := binaryBiproductData _ hT zero (section_ T.mor₂) (by simp) fst
    (by simp only [← hfst, sub_add_cancel])
state_before: case intro
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
d : BinaryBiproductData T.obj₁ T.obj₃ := binaryBiproductData T hT zero (section_ T.mor₂) ⋯ fst ⋯
⊢ ∃ e, T.mor₁ ≫ e.hom = biprod.inl ∧ T.mor₂ = e.hom ≫ biprod.snd
state_after: case intro
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
d : BinaryBiproductData T.obj₁ T.obj₃ := binaryBiproductData T hT zero (section_ T.mor₂) ⋯ fst ⋯
⊢ T.mor₁ ≫ (biprod.uniqueUpToIso T.obj₁ T.obj₃ d.isBilimit).hom = biprod.inl
tactic: refine ⟨biprod.uniqueUpToIso _ _ d.isBilimit, ⟨?_, by simp [d]⟩⟩
state_before: case intro
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
d : BinaryBiproductData T.obj₁ T.obj₃ := binaryBiproductData T hT zero (section_ T.mor₂) ⋯ fst ⋯
⊢ T.mor₁ ≫ (biprod.uniqueUpToIso T.obj₁ T.obj₃ d.isBilimit).hom = biprod.inl
state_after: case intro.h₀
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
d : BinaryBiproductData T.obj₁ T.obj₃ := binaryBiproductData T hT zero (section_ T.mor₂) ⋯ fst ⋯
⊢ (T.mor₁ ≫ (biprod.uniqueUpToIso T.obj₁ T.obj₃ d.isBilimit).hom) ≫ biprod.fst = biprod.inl ≫ biprod.fst

case intro.h₁
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
T : Triangle C
hT : T ∈ distinguishedTriangles
zero : T.mor₃ = 0
this✝ : Epi T.mor₂
this : IsSplitEpi T.mor₂
fst : T.obj₂ ⟶ T.obj₁
hfst : 𝟙 T.obj₂ - T.mor₂ ≫ section_ T.mor₂ = fst ≫ T.mor₁
d : BinaryBiproductData T.obj₁ T.obj₃ := binaryBiproductData T hT zero (section_ T.mor₂) ⋯ fst ⋯
⊢ (T.mor₁ ≫ (biprod.uniqueUpToIso T.obj₁ T.obj₃ d.isBilimit).hom) ≫ biprod.snd = biprod.inl ≫ biprod.snd
tactic: ext