Theorem: CategoryTheory.ShortComplex.isIso_homologyMap_of_isIso_cyclesMap_of_epi
File: Mathlib/Algebra/Homology/ShortComplex/Homology.lean

Proof steps:
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
⊢ IsIso (homologyMap φ)
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
⊢ IsIso (homologyMap φ)
tactic: have h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0 := by
    simp only [← cancel_epi φ.τ₁, ← toCycles_naturality_assoc,
      IsIso.hom_inv_id_assoc, toCycles_comp_homologyπ, comp_zero]
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
⊢ IsIso (homologyMap φ)
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
z : (CokernelCofork.ofπ S₂.homologyπ ⋯).pt ⟶ S₁.homology
hz : Cofork.π (CokernelCofork.ofπ S₂.homologyπ ⋯) ≫ z = inv (cyclesMap φ) ≫ S₁.homologyπ
⊢ IsIso (homologyMap φ)
tactic: have ⟨z, hz⟩ := CokernelCofork.IsColimit.desc' S₂.homologyIsCokernel _ h
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
z : (CokernelCofork.ofπ S₂.homologyπ ⋯).pt ⟶ S₁.homology
hz : Cofork.π (CokernelCofork.ofπ S₂.homologyπ ⋯) ≫ z = inv (cyclesMap φ) ≫ S₁.homologyπ
⊢ IsIso (homologyMap φ)
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
z : (CokernelCofork.ofπ S₂.homologyπ ⋯).pt ⟶ S₁.homology
hz : S₂.homologyπ ≫ z = inv (cyclesMap φ) ≫ S₁.homologyπ
⊢ IsIso (homologyMap φ)
tactic: dsimp at hz
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
z : (CokernelCofork.ofπ S₂.homologyπ ⋯).pt ⟶ S₁.homology
hz : S₂.homologyπ ≫ z = inv (cyclesMap φ) ≫ S₁.homologyπ
⊢ IsIso (homologyMap φ)
state_after: case refine_1
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
z : (CokernelCofork.ofπ S₂.homologyπ ⋯).pt ⟶ S₁.homology
hz : S₂.homologyπ ≫ z = inv (cyclesMap φ) ≫ S₁.homologyπ
⊢ homologyMap φ ≫ z = 𝟙 S₁.homology

case refine_2
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S S₁ S₂ S₃ S₄ : ShortComplex C
φ✝ : S₁ ⟶ S₂
h₁✝ : S₁.HomologyData
h₂✝ : S₂.HomologyData
A : C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (cyclesMap φ)
h₂ : Epi φ.τ₁
h : S₂.toCycles ≫ inv (cyclesMap φ) ≫ S₁.homologyπ = 0
z : (CokernelCofork.ofπ S₂.homologyπ ⋯).pt ⟶ S₁.homology
hz : S₂.homologyπ ≫ z = inv (cyclesMap φ) ≫ S₁.homologyπ
⊢ z ≫ homologyMap φ = 𝟙 S₂.homology
tactic: refine ⟨⟨z, ?_, ?_⟩⟩