Theorem: CategoryTheory.Abelian.Pseudoelement.epi_of_pseudo_surjective
File: Mathlib/CategoryTheory/Abelian/Pseudoelements.lean

Proof steps:
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
⊢ Function.Surjective (pseudoApply f) → Epi f
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
⊢ Epi f
tactic: intro h
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
⊢ Epi f
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
⊢ Epi f
tactic: have ⟨pbar, hpbar⟩ := h (𝟙 Q)
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
⊢ Epi f
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
⊢ Epi f
tactic: have ⟨p, hp⟩ := Quotient.exists_rep pbar
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
⊢ Epi f
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
⊢ Epi f
tactic: have : (⟦(p.hom ≫ f : Over Q)⟧ : Quotient (setoid Q)) = ⟦↑(𝟙 Q)⟧ := by
    rw [← hp] at hpbar
    exact hpbar
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
⊢ Epi f
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ (Over.mk (p.hom ≫ f)).hom = y ≫ (Over.mk (𝟙 Q)).hom
⊢ Epi f
tactic: have ⟨R, x, y, _, ey, comm⟩ := Quotient.exact this
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ (Over.mk (p.hom ≫ f)).hom = y ≫ (Over.mk (𝟙 Q)).hom
⊢ Epi f
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ (Over.mk (p.hom ≫ f)).hom = y ≫ (Over.mk (𝟙 Q)).hom
⊢ (x ≫ p.hom) ≫ f = y
tactic: apply @epi_of_epi_fac _ _ _ _ _ (x ≫ p.hom) f y ey
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ (Over.mk (p.hom ≫ f)).hom = y ≫ (Over.mk (𝟙 Q)).hom
⊢ (x ≫ p.hom) ≫ f = y
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ p.hom ≫ f = y ≫ 𝟙 Q
⊢ (x ≫ p.hom) ≫ f = y
tactic: dsimp at comm
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ p.hom ≫ f = y ≫ 𝟙 Q
⊢ (x ≫ p.hom) ≫ f = y
state_after: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ p.hom ≫ f = y ≫ 𝟙 Q
⊢ y ≫ 𝟙 Q = y
tactic: rw [Category.assoc, comm]
state_before: C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : Abelian C
P Q : C
f : P ⟶ Q
h : Function.Surjective (pseudoApply f)
pbar : Pseudoelement P
hpbar : pseudoApply f pbar = Quot.mk (PseudoEqual Q) (Over.mk (𝟙 Q))
p : Over P
hp : ⟦p⟧ = pbar
this : ⟦Over.mk (p.hom ≫ f)⟧ = ⟦Over.mk (𝟙 Q)⟧
R : C
x : R ⟶ (Over.mk (p.hom ≫ f)).left
y : R ⟶ (Over.mk (𝟙 Q)).left
w✝ : Epi x
ey : Epi y
comm : x ≫ p.hom ≫ f = y ≫ 𝟙 Q
⊢ y ≫ 𝟙 Q = y
state_after: no goals
tactic: apply Category.comp_id