Theorem: CategoryTheory.Limits.binaryBiconeOfIsSplitEpiOfKernel_snd
File: Mathlib/CategoryTheory/Preadditive/Biproducts.lean

Proof steps:
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ Fork.ι c ≫ (𝟙 X - (𝟙 X - f ≫ section_ f)) = 0
state_after: no goals
tactic: simp
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
c' : KernelFork (𝟙 X - (𝟙 X - f ≫ section_ f)) := KernelFork.ofι (Fork.ι c) ⋯
⊢ 𝟙 X - (𝟙 X - f ≫ section_ f) = f ≫ section_ f
state_after: no goals
tactic: simp
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
c' : KernelFork (𝟙 X - (𝟙 X - f ≫ section_ f)) := KernelFork.ofι (Fork.ι c) ⋯
i' : IsLimit c' := isKernelCompMono i (section_ f) ⋯
i'' : IsLimit (forkOfKernelFork c') := isLimitForkOfKernelFork i'
⊢ (𝟙 X - f ≫ section_ f) ≫ (𝟙 X - f ≫ section_ f) = 𝟙 X - f ≫ section_ f
state_after: no goals
tactic: simp
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ (Fork.ι c ≫
      let c' := KernelFork.ofι (Fork.ι c) ⋯;
      let i' := isKernelCompMono i (section_ f) ⋯;
      let i'' := isLimitForkOfKernelFork i';
      (splitMonoOfIdempotentOfIsLimitFork C ⋯ i'').retraction) =
    𝟙 c.pt
state_after: no goals
tactic: apply SplitMono.id
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ Fork.ι c ≫ f = 0
state_after: no goals
tactic: simp
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ (section_ f ≫
      let c' := KernelFork.ofι (Fork.ι c) ⋯;
      let i' := isKernelCompMono i (section_ f) ⋯;
      let i'' := isLimitForkOfKernelFork i';
      (splitMonoOfIdempotentOfIsLimitFork C ⋯ i'').retraction) =
    0
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ section_ f ≫
      (splitMonoOfIdempotentOfIsLimitFork C ⋯
          (isLimitForkOfKernelFork (isKernelCompMono i (section_ f) ⋯))).retraction =
    0
tactic: dsimp only
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ section_ f ≫
      (splitMonoOfIdempotentOfIsLimitFork C ⋯
          (isLimitForkOfKernelFork (isKernelCompMono i (section_ f) ⋯))).retraction =
    0
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ section_ f ≫ i.lift (Fork.ofι (Fork.ι (kernelForkOfFork (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯))) ⋯) = 0
tactic: rw [splitMonoOfIdempotentOfIsLimitFork_retraction, isLimitForkOfKernelFork_lift,
        isKernelCompMono_lift]
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ section_ f ≫ i.lift (Fork.ofι (Fork.ι (kernelForkOfFork (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯))) ⋯) = 0
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ section_ f ≫ i.lift (Fork.ofι (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯).ι ⋯) = 0
tactic: dsimp only [kernelForkOfFork_ι]
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ section_ f ≫ i.lift (Fork.ofι (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯).ι ⋯) = 0
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
this : Mono (Fork.ι c) := mono_of_isLimit_fork i
⊢ section_ f ≫ i.lift (Fork.ofι (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯).ι ⋯) = 0
tactic: letI := mono_of_isLimit_fork i
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
this : Mono (Fork.ι c) := mono_of_isLimit_fork i
⊢ section_ f ≫ i.lift (Fork.ofι (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯).ι ⋯) = 0
state_after: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
this : Mono (Fork.ι c) := mono_of_isLimit_fork i
⊢ (section_ f ≫ i.lift (Fork.ofι (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯).ι ⋯)) ≫ Fork.ι c = 0
tactic: apply zero_of_comp_mono c.ι
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
this : Mono (Fork.ι c) := mono_of_isLimit_fork i
⊢ (section_ f ≫ i.lift (Fork.ofι (Fork.ofι (𝟙 X - f ≫ section_ f) ⋯).ι ⋯)) ≫ Fork.ι c = 0
state_after: no goals
tactic: simp only [comp_sub, Category.comp_id, Category.assoc, sub_self, Fork.IsLimit.lift_ι,
        Fork.ι_ofι, IsSplitEpi.id_assoc]
state_before: C : Type u
inst✝³ : Category.{v, u} C
inst✝² : Preadditive C
X✝ Y✝ : C
inst✝¹ : HasBinaryBiproduct X✝ Y✝
X Y : C
f : X ⟶ Y
inst✝ : IsSplitEpi f
c : KernelFork f
i : IsLimit c
⊢ section_ f ≫ f = 𝟙 Y
state_after: no goals
tactic: simp