Module: Mathlib.Topology.Category.TopCat.Limits.Cofiltered

Goal state before:
pp: case e'_3.mpr.refine_1
J : Type v
inst✝¹ : Category.{w, v} J
inst✝ : IsCofiltered J
F : J ⥤ TopCat
C : Cone F
hC : IsLimit C
T : (j : J) → Set (Set ↑(F.obj j))
hT : ∀ (j : J), IsTopologicalBasis (T j)
univ : ∀ (i : J), Set.univ ∈ T i
inter : ∀ (i : J) (U1 U2 : Set ↑(F.obj i)), U1 ∈ T i → U2 ∈ T i → U1 ∩ U2 ∈ T i
compat : ∀ (i j : J) (f : i ⟶ j), ∀ V ∈ T j, ⇑(ConcreteCategory.hom (F.map f)) ⁻¹' V ∈ T i
U0 : Set ↑C.pt
U : (i : J) → Set ↑(F.obj i)
G : Finset J
h1 : ∀ i ∈ G, U i ∈ T i
h2 : U0 = ⋂ i ∈ G, (fun x ↦ (ConcreteCategory.hom (C.π.app i)) x) ⁻¹' U i
j : J
hj : ∀ {X : J}, X ∈ G → Nonempty (j ⟶ X)
g : (e : J) → e ∈ G → (j ⟶ e) := fun x he ↦ ⋯.some
Vs : J → Set ↑(F.obj j) := fun e ↦ if h : e ∈ G then ⇑(ConcreteCategory.hom (F.map (g e h))) ⁻¹' U e else Set.univ
V : Set ↑(F.obj j) := ⋂ e ∈ G, Vs e
⊢ V ∈ T j

pp: case e'_3.mpr.refine_2
J : Type v
inst✝¹ : Category.{w, v} J
inst✝ : IsCofiltered J
F : J ⥤ TopCat
C : Cone F
hC : IsLimit C
T : (j : J) → Set (Set ↑(F.obj j))
hT : ∀ (j : J), IsTopologicalBasis (T j)
univ : ∀ (i : J), Set.univ ∈ T i
inter : ∀ (i : J) (U1 U2 : Set ↑(F.obj i)), U1 ∈ T i → U2 ∈ T i → U1 ∩ U2 ∈ T i
compat : ∀ (i j : J) (f : i ⟶ j), ∀ V ∈ T j, ⇑(ConcreteCategory.hom (F.map f)) ⁻¹' V ∈ T i
U0 : Set ↑C.pt
U : (i : J) → Set ↑(F.obj i)
G : Finset J
h1 : ∀ i ∈ G, U i ∈ T i
h2 : U0 = ⋂ i ∈ G, (fun x ↦ (ConcreteCategory.hom (C.π.app i)) x) ⁻¹' U i
j : J
hj : ∀ {X : J}, X ∈ G → Nonempty (j ⟶ X)
g : (e : J) → e ∈ G → (j ⟶ e) := fun x he ↦ ⋯.some
Vs : J → Set ↑(F.obj j) := fun e ↦ if h : e ∈ G then ⇑(ConcreteCategory.hom (F.map (g e h))) ⁻¹' U e else Set.univ
V : Set ↑(F.obj j) := ⋂ e ∈ G, Vs e
⊢ U0 = ⇑(ConcreteCategory.hom (C.π.app j)) ⁻¹' V

Tactic:
· -- An intermediate claim used to apply induction along `G : Finset J` later on.
      have :
        ∀ (S : Set (Set (F.obj j))) (E : Finset J) (P : J → Set (F.obj j)) (_univ : Set.univ ∈ S)
          (_inter : ∀ A B : Set (F.obj j), A ∈ S → B ∈ S → A ∩ B ∈ S)
          (_cond : ∀ (e : J) (_he : e ∈ E), P e ∈ S), (⋂ (e) (_he : e ∈ E), P e) ∈ S := by
        intro S E
        induction E using Finset.induction_on with
        | empty =>
          intro P he _hh
          simpa
        | insert a E _ha hh1 =>
          intro hh2 hh3 hh4 hh5
          rw [Finset.set_biInter_insert]
          refine hh4 _ _ (hh5 _ (Finset.mem_insert_self _ _)) (hh1 _ hh3 hh4 ?_)
          intro e he
          exact hh5 e (Finset.mem_insert_of_mem he)
      -- use the intermediate claim to finish off the goal using `univ` and `inter`.
      refine this _ _ _ (univ _) (inter _) ?_
      intro e he
      dsimp [Vs]
      rw [dif_pos he]
      exact compat j e (g e he) (U e) (h1 e he)

Goal state after:
case e'_3.mpr.refine_2
J : Type v
inst✝¹ : Category.{w, v} J
inst✝ : IsCofiltered J
F : J ⥤ TopCat
C : Cone F
hC : IsLimit C
T : (j : J) → Set (Set ↑(F.obj j))
hT : ∀ (j : J), IsTopologicalBasis (T j)
univ : ∀ (i : J), Set.univ ∈ T i
inter : ∀ (i : J) (U1 U2 : Set ↑(F.obj i)), U1 ∈ T i → U2 ∈ T i → U1 ∩ U2 ∈ T i
compat : ∀ (i j : J) (f : i ⟶ j), ∀ V ∈ T j, ⇑(ConcreteCategory.hom (F.map f)) ⁻¹' V ∈ T i
U0 : Set ↑C.pt
U : (i : J) → Set ↑(F.obj i)
G : Finset J
h1 : ∀ i ∈ G, U i ∈ T i
h2 : U0 = ⋂ i ∈ G, (fun x ↦ (ConcreteCategory.hom (C.π.app i)) x) ⁻¹' U i
j : J
hj : ∀ {X : J}, X ∈ G → Nonempty (j ⟶ X)
g : (e : J) → e ∈ G → (j ⟶ e) := fun x he ↦ ⋯.some
Vs : J → Set ↑(F.obj j) := fun e ↦ if h : e ∈ G then ⇑(ConcreteCategory.hom (F.map (g e h))) ⁻¹' U e else Set.univ
V : Set ↑(F.obj j) := ⋂ e ∈ G, Vs e
⊢ U0 = ⇑(ConcreteCategory.hom (C.π.app j)) ⁻¹' V