Theorem: CategoryTheory.exact_f_d
File: Mathlib/CategoryTheory/Abelian/InjectiveResolution.lean

Proof steps:
state_before: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
⊢ f ≫ d f = 0
state_after: no goals
tactic: simp
state_before: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
⊢ (ShortComplex.mk f (d f) ⋯).Exact
state_after: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
⊢ (ShortComplex.mk f (d f) ⋯).Exact
tactic: let α : ShortComplex.mk f (cokernel.π f) (by simp) ⟶ ShortComplex.mk f (d f) (by simp) :=
    { τ₁ := 𝟙 _
      τ₂ := 𝟙 _
      τ₃ := Injective.ι _  }
state_before: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
⊢ (ShortComplex.mk f (d f) ⋯).Exact
state_after: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this : Epi α.τ₁
⊢ (ShortComplex.mk f (d f) ⋯).Exact
tactic: have : Epi α.τ₁ := by dsimp; infer_instance
state_before: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this : Epi α.τ₁
⊢ (ShortComplex.mk f (d f) ⋯).Exact
state_after: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝ : Epi α.τ₁
this : IsIso α.τ₂
⊢ (ShortComplex.mk f (d f) ⋯).Exact
tactic: have : IsIso α.τ₂ := by dsimp; infer_instance
state_before: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝ : Epi α.τ₁
this : IsIso α.τ₂
⊢ (ShortComplex.mk f (d f) ⋯).Exact
state_after: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝¹ : Epi α.τ₁
this✝ : IsIso α.τ₂
this : Mono α.τ₃
⊢ (ShortComplex.mk f (d f) ⋯).Exact
tactic: have : Mono α.τ₃ := by dsimp; infer_instance
state_before: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝¹ : Epi α.τ₁
this✝ : IsIso α.τ₂
this : Mono α.τ₃
⊢ (ShortComplex.mk f (d f) ⋯).Exact
state_after: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝¹ : Epi α.τ₁
this✝ : IsIso α.τ₂
this : Mono α.τ₃
⊢ (ShortComplex.mk f (cokernel.π f) ⋯).Exact
tactic: rw [← ShortComplex.exact_iff_of_epi_of_isIso_of_mono α]
state_before: C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝¹ : Epi α.τ₁
this✝ : IsIso α.τ₂
this : Mono α.τ₃
⊢ (ShortComplex.mk f (cokernel.π f) ⋯).Exact
state_after: case hS
C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝¹ : Epi α.τ₁
this✝ : IsIso α.τ₂
this : Mono α.τ₃
⊢ IsColimit (CokernelCofork.ofπ (ShortComplex.mk f (cokernel.π f) ⋯).g ⋯)
tactic: apply ShortComplex.exact_of_g_is_cokernel
state_before: case hS
C : Type u
inst✝² : Category.{v, u} C
inst✝¹ : Abelian C
inst✝ : EnoughInjectives C
X Y : C
f : X ⟶ Y
α : ShortComplex.mk f (cokernel.π f) ⋯ ⟶ ShortComplex.mk f (d f) ⋯ :=
  { τ₁ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₁, τ₂ := 𝟙 (ShortComplex.mk f (cokernel.π f) ⋯).X₂,
    τ₃ := ι (ShortComplex.mk f (cokernel.π f) ⋯).X₃, comm₁₂ := ⋯, comm₂₃ := ⋯ }
this✝¹ : Epi α.τ₁
this✝ : IsIso α.τ₂
this : Mono α.τ₃
⊢ IsColimit (CokernelCofork.ofπ (ShortComplex.mk f (cokernel.π f) ⋯).g ⋯)
state_after: no goals
tactic: apply cokernelIsCokernel