-- Mathlib/Topology/Category/CompHaus/EffectiveEpi.lean
theorem effectiveEpiFamily_tfae
    {α : Type} [Finite α] {B : CompHaus.{u}}
    (X : α → CompHaus.{u}) (π : (a : α) → (X a ⟶ B)) :
    TFAE
    [ EffectiveEpiFamily X π
    , Epi (Sigma.desc π)
    , ∀ b : B, ∃ (a : α) (x : X a), π a x = b
    ]

Proof state:
case intro.w.mk
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
x✝ : Epi (Sigma.desc π)
e : Function.Surjective ⇑(ConcreteCategory.hom (Sigma.desc π))
i : ∐ X ≅ finiteCoproduct X :=
  (colimit.isColimit (Discrete.functor X)).coconePointUniqueUpToIso (finiteCoproduct.isColimit X)
t : ↑(∐ X).toTop
q : (fun X => ↑X.toTop) (finiteCoproduct X) := (ConcreteCategory.hom i.hom) t
this : t = (ConcreteCategory.hom i.inv) ((ConcreteCategory.hom i.hom) t)
a : α
⊢ π a = finiteCoproduct.ι X a ≫ finiteCoproduct.desc X π

Tactic:
ext

Result:
case intro.w.mk.h.h
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
x✝ : Epi (Sigma.desc π)
e : Function.Surjective ⇑(ConcreteCategory.hom (Sigma.desc π))
i : ∐ X ≅ finiteCoproduct X :=
  (colimit.isColimit (Discrete.functor X)).coconePointUniqueUpToIso (finiteCoproduct.isColimit X)
t : ↑(∐ X).toTop
q : (fun X => ↑X.toTop) (finiteCoproduct X) := (ConcreteCategory.hom i.hom) t
this : t = (ConcreteCategory.hom i.inv) ((ConcreteCategory.hom i.hom) t)
a : α
a✝ : ↑(X a).toTop
⊢ (ConcreteCategory.hom (π a)) a✝ = (ConcreteCategory.hom (finiteCoproduct.ι X a ≫ finiteCoproduct.desc X π)) a✝

Proof state:
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
⊢ [EffectiveEpiFamily X π, Epi (Sigma.desc π), ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b].TFAE

Tactic:
tfae_have 2 → 3
| e => by
  rw [epi_iff_surjective] at e
  let i : ∐ X ≅ finiteCoproduct X :=
    (colimit.isColimit _).coconePointUniqueUpToIso (finiteCoproduct.isColimit _)
  intro b
  obtain ⟨t, rfl⟩ := e b
  let q := i.hom t
  refine ⟨q.1,q.2,?_⟩
  have : t = i.inv (i.hom t) := show t = (i.hom ≫ i.inv) t by simp only [i.hom_inv_id]; rfl
  rw [this]
  show _ = (i.inv ≫ Sigma.desc π) (i.hom t)
  suffices i.inv ≫ Sigma.desc π = finiteCoproduct.desc X π by
    rw [this]; rfl
  rw [Iso.inv_comp_eq]
  apply colimit.hom_ext
  rintro ⟨a⟩
  simp only [i, Discrete.functor_obj, colimit.ι_desc, Cofan.mk_pt, Cofan.mk_ι_app,
    colimit.comp_coconePointUniqueUpToIso_hom_assoc]
  ext; rfl

Result:
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
tfae_2_to_3 : Epi (Sigma.desc π) → ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b
⊢ [EffectiveEpiFamily X π, Epi (Sigma.desc π), ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b].TFAE

Proof state:
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
x✝ : Epi (Sigma.desc π)
e : Function.Surjective ⇑(ConcreteCategory.hom (Sigma.desc π))
i : ∐ X ≅ finiteCoproduct X :=
  (colimit.isColimit (Discrete.functor X)).coconePointUniqueUpToIso (finiteCoproduct.isColimit X)
t : ↑(∐ X).toTop
q : (fun X => ↑X.toTop) (finiteCoproduct X) := (ConcreteCategory.hom i.hom) t
⊢ t = (ConcreteCategory.hom (𝟙 (∐ X))) t

Tactic:
rfl

Result:
no goals

Proof state:
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
tfae_2_to_3 : Epi (Sigma.desc π) → ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b
⊢ [EffectiveEpiFamily X π, Epi (Sigma.desc π), ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b].TFAE

Tactic:
tfae_finish

Result:
no goals

Proof state:
case intro
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
x✝ : Epi (Sigma.desc π)
e : Function.Surjective ⇑(ConcreteCategory.hom (Sigma.desc π))
i : ∐ X ≅ finiteCoproduct X :=
  (colimit.isColimit (Discrete.functor X)).coconePointUniqueUpToIso (finiteCoproduct.isColimit X)
t : ↑(∐ X).toTop
q : (fun X => ↑X.toTop) (finiteCoproduct X) := (ConcreteCategory.hom i.hom) t
⊢ ∃ a x, (ConcreteCategory.hom (π a)) x = (ConcreteCategory.hom (Sigma.desc π)) t

Tactic:
refine ⟨q.1,q.2,?_⟩

Result:
case intro
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
tfae_3_to_2 : (∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b) → Epi (Sigma.desc π)
x✝ : Epi (Sigma.desc π)
e : Function.Surjective ⇑(ConcreteCategory.hom (Sigma.desc π))
i : ∐ X ≅ finiteCoproduct X :=
  (colimit.isColimit (Discrete.functor X)).coconePointUniqueUpToIso (finiteCoproduct.isColimit X)
t : ↑(∐ X).toTop
q : (fun X => ↑X.toTop) (finiteCoproduct X) := (ConcreteCategory.hom i.hom) t
⊢ (ConcreteCategory.hom (π q.fst)) q.snd = (ConcreteCategory.hom (Sigma.desc π)) t

Proof state:
case intro.intro
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
x✝ : ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b
e : ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b := x✝
b : ↑B.toTop
t : α
x : ↑(X t).toTop
h : (ConcreteCategory.hom (π t)) x = b
⊢ (ConcreteCategory.hom (Sigma.desc π)) ((ConcreteCategory.hom (Sigma.ι X t)) x) = b

Tactic:
change (Sigma.ι X t ≫ Sigma.desc π) x = _

Result:
case intro.intro
α : Type
inst✝ : Finite α
B : CompHaus
X : α → CompHaus
π : (a : α) → X a ⟶ B
tfae_2_to_1 : Epi (Sigma.desc π) → EffectiveEpiFamily X π
tfae_1_to_2 : EffectiveEpiFamily X π → Epi (Sigma.desc π)
x✝ : ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b
e : ∀ (b : ↑B.toTop), ∃ a x, (ConcreteCategory.hom (π a)) x = b := x✝
b : ↑B.toTop
t : α
x : ↑(X t).toTop
h : (ConcreteCategory.hom (π t)) x = b
⊢ (ConcreteCategory.hom (Sigma.ι X t ≫ Sigma.desc π)) x = b