Theorem: CategoryTheory.ShortComplex.Splitting.leftHomologyData_K
File: Mathlib/Algebra/Homology/ShortComplex/Exact.lean

Proof steps:
state_before: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
⊢ S.LeftHomologyData
state_after: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
⊢ S.LeftHomologyData
tactic: have hi := KernelFork.IsLimit.ofι S.f S.zero
    (fun x _ => x ≫ s.r)
    (fun x hx => by simp only [assoc, s.r_f, comp_sub, comp_id,
      sub_eq_self, reassoc_of% hx, zero_comp])
    (fun x _ b hb => by simp only [← hb, assoc, f_r, comp_id])
state_before: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
⊢ S.LeftHomologyData
state_after: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
⊢ S.LeftHomologyData
tactic: let f' := hi.lift (KernelFork.ofι S.f S.zero)
state_before: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
⊢ S.LeftHomologyData
state_after: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
hf' : f' = 𝟙 (KernelFork.ofι S.f ⋯).pt
⊢ S.LeftHomologyData
tactic: have hf' : f' = 𝟙 _ := by
    apply Fork.IsLimit.hom_ext hi
    dsimp
    erw [Fork.IsLimit.lift_ι hi]
    simp only [Fork.ι_ofι, id_comp]
state_before: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
hf' : f' = 𝟙 (KernelFork.ofι S.f ⋯).pt
⊢ S.LeftHomologyData
state_after: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
hf' : f' = 𝟙 (KernelFork.ofι S.f ⋯).pt
wπ : f' ≫ 0 = 0
⊢ S.LeftHomologyData
tactic: have wπ : f' ≫ (0 : S.X₁ ⟶ 0) = 0 := comp_zero
state_before: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
hf' : f' = 𝟙 (KernelFork.ofι S.f ⋯).pt
wπ : f' ≫ 0 = 0
⊢ S.LeftHomologyData
state_after: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
hf' : f' = 𝟙 (KernelFork.ofι S.f ⋯).pt
wπ : f' ≫ 0 = 0
hπ : IsColimit (CokernelCofork.ofπ 0 wπ)
⊢ S.LeftHomologyData
tactic: have hπ : IsColimit (CokernelCofork.ofπ 0 wπ) := CokernelCofork.IsColimit.ofEpiOfIsZero _
      (by rw [hf']; infer_instance) (isZero_zero _)
state_before: C : Type u_1
D : Type u_2
inst✝⁴ : Category.{?u.84186, u_1} C
inst✝³ : Category.{?u.84190, u_2} D
inst✝² : Preadditive C
inst✝¹ : Preadditive D
S : ShortComplex C
inst✝ : HasZeroObject C
s : S.Splitting
hi : IsLimit (KernelFork.ofι S.f ⋯)
f' : (KernelFork.ofι S.f ⋯).pt ⟶ (KernelFork.ofι S.f ⋯).pt := hi.lift (KernelFork.ofι S.f ⋯)
hf' : f' = 𝟙 (KernelFork.ofι S.f ⋯).pt
wπ : f' ≫ 0 = 0
hπ : IsColimit (CokernelCofork.ofπ 0 wπ)
⊢ S.LeftHomologyData
state_after: no goals
tactic: exact
    { K := S.X₁
      H := 0
      i := S.f
      wi := S.zero
      hi := hi
      π := 0
      wπ := wπ
      hπ := hπ }