Module: Mathlib.CategoryTheory.Abelian.DiagramLemmas.Four

Goal state before:
pp: C : Type u_1
inst✝¹ : Category.{v_1, u_1} C
inst✝ : Abelian C
R₁ R₂ : ComposableArrows C 3
φ : R₁ ⟶ R₂
hR₁ : R₁.map' 0 2 mono_of_epi_of_mono_of_mono'._proof_2 mono_of_epi_of_mono_of_mono'._proof_4 = 0
hR₁' :
  (mk₂ (R₁.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)
      (R₁.map' 2 3 mono_of_epi_of_mono_of_mono'._proof_4 mono_of_epi_of_mono_of_mono'._proof_7)).Exact
hR₂ :
  (mk₂ (R₂.map' 0 1 mono_of_epi_of_mono_of_mono'._proof_9 mono_of_epi_of_mono_of_mono'._proof_11)
      (R₂.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)).Exact
h₀ : Epi (app' φ 0 mono_of_epi_of_mono_of_mono'._proof_13)
h₁✝ : Mono (app' φ 1 mono_of_epi_of_mono_of_mono'._proof_11)
h₃✝ : Mono (app' φ 3 mono_of_epi_of_mono_of_mono'._proof_7)
A : C
f₂ : A ⟶ R₁.obj' 2 mono_of_epi_of_mono_of_mono'._proof_4
h₁ : f₂ ≫ app' φ 2 mono_of_epi_of_mono_of_mono'._proof_4 = 0
h₂ : f₂ ≫ R₁.map' 2 3 ⋯ ⋯ = 0
A₁ : C
π₁ : A₁ ⟶ A
w✝ : Epi π₁
f₁ :
  A₁ ⟶
    ((mk₂ (R₁.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)
            (R₁.map' 2 3 mono_of_epi_of_mono_of_mono'._proof_4 mono_of_epi_of_mono_of_mono'._proof_7)).sc
        ⋯ 0 ⋯).X₁
hf₁ : π₁ ≫ f₂ = f₁ ≫ R₁.map (homOfLE ⋯)
h₃ : (f₁ ≫ app' φ 1 ⋯) ≫ R₂.map' 1 2 ⋯ ⋯ = 0
⊢ f₂ = 0

Tactic:
obtain ⟨A₂, π₂, _, g₀, hg₀⟩ := (hR₂.exact 0).exact_up_to_refinements _ h₃

Goal state after:
C : Type u_1
inst✝¹ : Category.{v_1, u_1} C
inst✝ : Abelian C
R₁ R₂ : ComposableArrows C 3
φ : R₁ ⟶ R₂
hR₁ : R₁.map' 0 2 mono_of_epi_of_mono_of_mono'._proof_2 mono_of_epi_of_mono_of_mono'._proof_4 = 0
hR₁' :
  (mk₂ (R₁.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)
      (R₁.map' 2 3 mono_of_epi_of_mono_of_mono'._proof_4 mono_of_epi_of_mono_of_mono'._proof_7)).Exact
hR₂ :
  (mk₂ (R₂.map' 0 1 mono_of_epi_of_mono_of_mono'._proof_9 mono_of_epi_of_mono_of_mono'._proof_11)
      (R₂.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)).Exact
h₀ : Epi (app' φ 0 mono_of_epi_of_mono_of_mono'._proof_13)
h₁✝ : Mono (app' φ 1 mono_of_epi_of_mono_of_mono'._proof_11)
h₃✝ : Mono (app' φ 3 mono_of_epi_of_mono_of_mono'._proof_7)
A : C
f₂ : A ⟶ R₁.obj' 2 mono_of_epi_of_mono_of_mono'._proof_4
h₁ : f₂ ≫ app' φ 2 mono_of_epi_of_mono_of_mono'._proof_4 = 0
h₂ : f₂ ≫ R₁.map' 2 3 ⋯ ⋯ = 0
A₁ : C
π₁ : A₁ ⟶ A
w✝¹ : Epi π₁
f₁ :
  A₁ ⟶
    ((mk₂ (R₁.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)
            (R₁.map' 2 3 mono_of_epi_of_mono_of_mono'._proof_4 mono_of_epi_of_mono_of_mono'._proof_7)).sc
        ⋯ 0 ⋯).X₁
hf₁ : π₁ ≫ f₂ = f₁ ≫ R₁.map (homOfLE ⋯)
h₃ : (f₁ ≫ app' φ 1 ⋯) ≫ R₂.map' 1 2 ⋯ ⋯ = 0
A₂ : C
π₂ : A₂ ⟶ A₁
w✝ : Epi π₂
g₀ :
  A₂ ⟶
    ((mk₂ (R₂.map' 0 1 mono_of_epi_of_mono_of_mono'._proof_9 mono_of_epi_of_mono_of_mono'._proof_11)
            (R₂.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)).sc
        ⋯ 0 ⋯).X₁
hg₀ :
  π₂ ≫ f₁ ≫ app' φ 1 ⋯ =
    g₀ ≫
      ((mk₂ (R₂.map' 0 1 mono_of_epi_of_mono_of_mono'._proof_9 mono_of_epi_of_mono_of_mono'._proof_11)
              (R₂.map' 1 2 mono_of_epi_of_mono_of_mono'._proof_6 mono_of_epi_of_mono_of_mono'._proof_4)).sc
          ⋯ 0 ⋯).f
⊢ f₂ = 0