l3lab/ntp-mathlib huggingface dataset:
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      

Proof state:
case intro.intro.refine'_1
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
this : Set.Countable v0
⊢ Set.Countable v

Next tactic:
exact this.preimage SetLike.coe_injective
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · 

Proof state:
case intro.intro.refine'_2
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
⊢ Dense v

Next tactic:
refine' fun t => mem_closure_iff.2 fun ε εpos => _
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      

Proof state:
case intro.intro.refine'_2
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
⊢ ∃ y ∈ v, edist t y < ε

Next tactic:
rcases exists_between εpos with ⟨δ, δpos, δlt⟩
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      

Proof state:
case intro.intro.refine'_2.intro.intro
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
⊢ ∃ y ∈ v, edist t y < ε

Next tactic:
have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      

Proof state:
case intro.intro.refine'_2.intro.intro
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
⊢ ∃ y ∈ v, edist t y < ε

Next tactic:
have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        intro x
        rcases mem_closure_iff.1 (s_dense x) (δ / 2) δpos' with ⟨y, ys, hy⟩
        exact ⟨y, ⟨ys, hy⟩⟩
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        

Proof state:
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
⊢ ∀ (x : α), ∃ y ∈ s, edist x y < δ / 2

Next tactic:
intro x
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        intro x
        

Proof state:
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
x : α
⊢ ∃ y ∈ s, edist x y < δ / 2

Next tactic:
rcases mem_closure_iff.1 (s_dense x) (δ / 2) δpos' with ⟨y, ys, hy⟩
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        intro x
        rcases mem_closure_iff.1 (s_dense x) (δ / 2) δpos' with ⟨y, ys, hy⟩
        

Proof state:
case intro.intro
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
x y : α
ys : y ∈ s
hy : edist x y < δ / 2
⊢ ∃ y ∈ s, edist x y < δ / 2

Next tactic:
exact ⟨y, ⟨ys, hy⟩⟩
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        intro x
        rcases mem_closure_iff.1 (s_dense x) (δ / 2) δpos' with ⟨y, ys, hy⟩
        exact ⟨y, ⟨ys, hy⟩⟩
      

Proof state:
case intro.intro.refine'_2.intro.intro
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
Exy : ∀ (x : α), ∃ y ∈ s, edist x y < δ / 2
⊢ ∃ y ∈ v, edist t y < ε

Next tactic:
let F x := choose (Exy x)
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        intro x
        rcases mem_closure_iff.1 (s_dense x) (δ / 2) δpos' with ⟨y, ys, hy⟩
        exact ⟨y, ⟨ys, hy⟩⟩
      let F x := choose (Exy x)
      

Proof state:
case intro.intro.refine'_2.intro.intro
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
Exy : ∀ (x : α), ∃ y ∈ s, edist x y < δ / 2
F : α → α := fun x => choose (_ : ∃ y ∈ s, edist x y < δ / 2)
⊢ ∃ y ∈ v, edist t y < ε

Next tactic:
have Fspec : ∀ x, F x ∈ s ∧ edist x (F x) < δ / 2 := fun x => choose_spec (Exy x)
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        intro x
        rcases mem_closure_iff.1 (s_dense x) (δ / 2) δpos' with ⟨y, ys, hy⟩
        exact ⟨y, ⟨ys, hy⟩⟩
      let F x := choose (Exy x)
      have Fspec : ∀ x, F x ∈ s ∧ edist x (F x) < δ / 2 := fun x => choose_spec (Exy x)
      -- cover `t` with finitely many balls. Their centers form a set `a`
      

Proof state:
case intro.intro.refine'_2.intro.intro
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
Exy : ∀ (x : α), ∃ y ∈ s, edist x y < δ / 2
F : α → α := fun x => choose (_ : ∃ y ∈ s, edist x y < δ / 2)
Fspec : ∀ (x : α), F x ∈ s ∧ edist x (F x) < δ / 2
⊢ ∃ y ∈ v, edist t y < ε

Next tactic:
have : TotallyBounded (t : Set α) := t.isCompact.totallyBounded
/-- In a second countable space, the type of nonempty compact subsets is second countable -/
instance NonemptyCompacts.secondCountableTopology [SecondCountableTopology α] :
    SecondCountableTopology (NonemptyCompacts α) :=
  haveI : SeparableSpace (NonemptyCompacts α) := by
    /- To obtain a countable dense subset of `NonemptyCompacts α`, start from
        a countable dense subset `s` of α, and then consider all its finite nonempty subsets.
        This set is countable and made of nonempty compact sets. It turns out to be dense:
        by total boundedness, any compact set `t` can be covered by finitely many small balls, and
        approximations in `s` of the centers of these balls give the required finite approximation
        of `t`. -/
    rcases exists_countable_dense α with ⟨s, cs, s_dense⟩
    let v0 := { t : Set α | t.Finite ∧ t ⊆ s }
    let v : Set (NonemptyCompacts α) := { t : NonemptyCompacts α | (t : Set α) ∈ v0 }
    refine' ⟨⟨v, _, _⟩⟩
    · have : v0.Countable := countable_setOf_finite_subset cs
      exact this.preimage SetLike.coe_injective
    · refine' fun t => mem_closure_iff.2 fun ε εpos => _
      -- t is a compact nonempty set, that we have to approximate uniformly by a a set in `v`.
      rcases exists_between εpos with ⟨δ, δpos, δlt⟩
      have δpos' : 0 < δ / 2 := ENNReal.half_pos δpos.ne'
      -- construct a map F associating to a point in α an approximating point in s, up to δ/2.
      have Exy : ∀ x, ∃ y, y ∈ s ∧ edist x y < δ / 2 := by
        intro x
        rcases mem_closure_iff.1 (s_dense x) (δ / 2) δpos' with ⟨y, ys, hy⟩
        exact ⟨y, ⟨ys, hy⟩⟩
      let F x := choose (Exy x)
      have Fspec : ∀ x, F x ∈ s ∧ edist x (F x) < δ / 2 := fun x => choose_spec (Exy x)
      -- cover `t` with finitely many balls. Their centers form a set `a`
      have : TotallyBounded (t : Set α) := t.isCompact.totallyBounded
      

Proof state:
case intro.intro.refine'_2.intro.intro
α : Type u
inst✝¹ : EMetricSpace α
s✝ : Set α
inst✝ : SecondCountableTopology α
s : Set α
cs : Set.Countable s
s_dense : Dense s
v0 : Set (Set α) := {t | Set.Finite t ∧ t ⊆ s}
v : Set (NonemptyCompacts α) := {t | ↑t ∈ v0}
t : NonemptyCompacts α
ε : ℝ≥0∞
εpos : ε > 0
δ : ℝ≥0∞
δpos : 0 < δ
δlt : δ < ε
δpos' : 0 < δ / 2
Exy : ∀ (x : α), ∃ y ∈ s, edist x y < δ / 2
F : α → α := fun x => choose (_ : ∃ y ∈ s, edist x y < δ / 2)
Fspec : ∀ (x : α), F x ∈ s ∧ edist x (F x) < δ / 2
this : TotallyBounded ↑t
⊢ ∃ y ∈ v, edist t y < ε

Next tactic:
rcases totallyBounded_iff.1 this (δ / 2) δpos' with ⟨a, af, ta⟩