Theorem: SemiNormedGrp.explicitCokernel_hom_ext
File: Mathlib/Analysis/Normed/Group/SemiNormedGrp/Kernels.lean

tactic: let g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
state_before: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
⊢ e₁ = e₂
state_after: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
⊢ e₁ = e₂

tactic: have w : f ≫ g = 0 := by simp [g]
state_before: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
⊢ e₁ = e₂
state_after: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
⊢ e₁ = e₂

tactic: have : e₂ = explicitCokernelDesc w := by apply explicitCokernelDesc_unique; rfl
state_before: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
⊢ e₁ = e₂
state_after: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
this : e₂ = explicitCokernelDesc w
⊢ e₁ = e₂

tactic: rw [this]
state_before: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
this : e₂ = explicitCokernelDesc w
⊢ e₁ = e₂
state_after: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
this : e₂ = explicitCokernelDesc w
⊢ e₁ = explicitCokernelDesc w

tactic: apply explicitCokernelDesc_unique
state_before: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
this : e₂ = explicitCokernelDesc w
⊢ e₁ = explicitCokernelDesc w
state_after: case he
X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
this : e₂ = explicitCokernelDesc w
⊢ explicitCokernelπ f ≫ e₁ = g

tactic: exact h
state_before: case he
X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
this : e₂ = explicitCokernelDesc w
⊢ explicitCokernelπ f ≫ e₁ = g
state_after: no goals

tactic: simp [g]
state_before: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
⊢ f ≫ g = 0
state_after: no goals

tactic: apply explicitCokernelDesc_unique
state_before: X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
⊢ e₂ = explicitCokernelDesc w
state_after: case he
X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
⊢ explicitCokernelπ f ≫ e₂ = g

tactic: rfl
state_before: case he
X Y Z : SemiNormedGrp
f : X ⟶ Y
e₁ e₂ : explicitCokernel f ⟶ Z
h : explicitCokernelπ f ≫ e₁ = explicitCokernelπ f ≫ e₂
g : Y ⟶ Z := explicitCokernelπ f ≫ e₂
w : f ≫ g = 0
⊢ explicitCokernelπ f ≫ e₂ = g
state_after: no goals