-- Mathlib/Algebra/Homology/ShortComplex/Homology.lean
lemma isIso_homologyMap_of_isIso_opcyclesMap_of_mono {φ : S₁ ⟶ S₂}
    [S₁.HasHomology] [S₂.HasHomology] (h₁ : IsIso (opcyclesMap φ)) (h₂ : Mono φ.τ₃) :
    IsIso (homologyMap φ)

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
⊢ IsIso (homologyMap φ)

Tactic:
have h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0 := by
  simp only [← cancel_mono φ.τ₃, zero_comp, assoc, ← fromOpcycles_naturality,
    IsIso.inv_hom_id_assoc, homologyι_comp_fromOpcycles]

Result:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
⊢ IsIso (homologyMap φ)

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
⊢ (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0

Tactic:
simp only [← cancel_mono φ.τ₃, zero_comp, assoc, ← fromOpcycles_naturality,
  IsIso.inv_hom_id_assoc, homologyι_comp_fromOpcycles]

Result:
no goals

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
⊢ IsIso (homologyMap φ)

Tactic:
have ⟨z, hz⟩ := KernelFork.IsLimit.lift' S₁.homologyIsKernel _ h

Result:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ Fork.ι (KernelFork.ofι S₁.homologyι ⋯) = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ IsIso (homologyMap φ)

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ S₁.homologyι = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ IsIso (homologyMap φ)

Tactic:
refine ⟨⟨z, ?_, ?_⟩⟩

Result:
case refine_1
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ S₁.homologyι = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ homologyMap φ ≫ z = 𝟙 S₁.homology

case refine_2
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ S₁.homologyι = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ z ≫ homologyMap φ = 𝟙 S₂.homology

Proof state:
case refine_2
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ S₁.homologyι = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ z ≫ homologyMap φ = 𝟙 S₂.homology

Tactic:
rw [← cancel_mono S₂.homologyι, assoc, homologyι_naturality, reassoc_of% hz,
  IsIso.inv_hom_id, comp_id, id_comp]

Result:
no goals

Proof state:
case refine_1
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ S₁.homologyι = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ homologyMap φ ≫ z = 𝟙 S₁.homology

Tactic:
rw [← cancel_mono S₁.homologyι, id_comp, assoc, hz, homologyι_naturality_assoc,
  IsIso.hom_inv_id, comp_id]

Result:
no goals

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ Fork.ι (KernelFork.ofι S₁.homologyι ⋯) = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ IsIso (homologyMap φ)

Tactic:
dsimp at hz

Result:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : HasZeroMorphisms C
S₁ S₂ : ShortComplex C
φ : S₁ ⟶ S₂
inst✝¹ : S₁.HasHomology
inst✝ : S₂.HasHomology
h₁ : IsIso (opcyclesMap φ)
h₂ : Mono φ.τ₃
h : (S₂.homologyι ≫ inv (opcyclesMap φ)) ≫ S₁.fromOpcycles = 0
z : S₂.homology ⟶ (KernelFork.ofι S₁.homologyι ⋯).pt
hz : z ≫ S₁.homologyι = S₂.homologyι ≫ inv (opcyclesMap φ)
⊢ IsIso (homologyMap φ)