-- Mathlib/Topology/ContinuousMap/Bounded/Basic.lean
theorem arzela_ascoli₁ [CompactSpace β] (A : Set (α →ᵇ β)) (closed : IsClosed A)
    (H : Equicontinuous ((↑) : A → α → β)) : IsCompact A

Proof state:
case intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Tactic:
have ε₂0 : ε₂ > 0 := half_pos (half_pos ε₁0)

Result:
case intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
ε₂0 : ε₂ > 0
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Proof state:
case intro.intro.intro.intro.intro.intro.intro.intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
ε₂0 : ε₂ > 0
U : α → Set α
hU : ∀ (x : α), x ∈ U x ∧ IsOpen (U x) ∧ ∀ y ∈ U x, ∀ z ∈ U x, ∀ {f : α →ᵇ β}, f ∈ A → dist (f y) (f z) < ε₂
tα : Set α
left✝¹ : tα ⊆ univ
hfin✝ : tα.Finite
htα : univ ⊆ ⋃ x ∈ tα, U x
val✝ : Fintype ↑tα
tβ : Set β
left✝ : tβ ⊆ univ
hfin : tβ.Finite
htβ : univ ⊆ ⋃ y ∈ tβ, ball y ε₂
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Tactic:
rcases hfin.nonempty_fintype with ⟨_⟩

Result:
case intro.intro.intro.intro.intro.intro.intro.intro.intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
ε₂0 : ε₂ > 0
U : α → Set α
hU : ∀ (x : α), x ∈ U x ∧ IsOpen (U x) ∧ ∀ y ∈ U x, ∀ z ∈ U x, ∀ {f : α →ᵇ β}, f ∈ A → dist (f y) (f z) < ε₂
tα : Set α
left✝¹ : tα ⊆ univ
hfin✝ : tα.Finite
htα : univ ⊆ ⋃ x ∈ tα, U x
val✝¹ : Fintype ↑tα
tβ : Set β
left✝ : tβ ⊆ univ
hfin : tβ.Finite
htβ : univ ⊆ ⋃ y ∈ tβ, ball y ε₂
val✝ : Fintype ↑tβ
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Proof state:
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : Equicontinuous fun x => ⇑↑x
⊢ IsCompact A

Tactic:
simp_rw [Equicontinuous, Metric.equicontinuousAt_iff_pair] at H

Result:
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
⊢ IsCompact A

Proof state:
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
⊢ TotallyBounded A

Tactic:
refine totallyBounded_of_finite_discretization fun ε ε0 => ?_

Result:
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Proof state:
case intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
ε₂0 : ε₂ > 0
this : ∀ (x : α), ∃ U, x ∈ U ∧ IsOpen U ∧ ∀ y ∈ U, ∀ z ∈ U, ∀ {f : α →ᵇ β}, f ∈ A → dist (f y) (f z) < ε₂
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Tactic:
choose U hU using this

Result:
case intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
ε₂0 : ε₂ > 0
U : α → Set α
hU : ∀ (x : α), x ∈ U x ∧ IsOpen (U x) ∧ ∀ y ∈ U x, ∀ z ∈ U x, ∀ {f : α →ᵇ β}, f ∈ A → dist (f y) (f z) < ε₂
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Proof state:
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
ε₂0 : ε₂ > 0
U : α → Set α
hU : ∀ (x : α), x ∈ U x ∧ IsOpen (U x) ∧ ∀ y ∈ U x, ∀ z ∈ U x, ∀ {f : α →ᵇ β}, f ∈ A → dist (f y) (f z) < ε₂
tα : Set α
left✝¹ : tα ⊆ univ
hfin✝ : tα.Finite
htα : univ ⊆ ⋃ x ∈ tα, U x
val✝¹ : Fintype ↑tα
tβ : Set β
left✝ : tβ ⊆ univ
hfin : tβ.Finite
htβ : univ ⊆ ⋃ y ∈ tβ, ball y ε₂
val✝ : Fintype ↑tβ
F : β → β
hF : ∀ (y : β), F y ∈ tβ ∧ dist y (F y) < ε₂
f : α →ᵇ β
hf : f ∈ A
g : α →ᵇ β
hg : g ∈ A
f_eq_g : (fun f a => ⟨F (↑f ↑a), ⋯⟩) ⟨f, hf⟩ = (fun f a => ⟨F (↑f ↑a), ⋯⟩) ⟨g, hg⟩
x x' : α
x'tα : x' ∈ tα
hx' : x ∈ U x'
⊢ ε₂ + ε₂ + ε₁ / 2 = ε₁

Tactic:
rw [add_halves, add_halves]

Result:
no goals

Proof state:
case refine_2
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
ε₂0 : ε₂ > 0
U : α → Set α
hU : ∀ (x : α), x ∈ U x ∧ IsOpen (U x) ∧ ∀ y ∈ U x, ∀ z ∈ U x, ∀ {f : α →ᵇ β}, f ∈ A → dist (f y) (f z) < ε₂
tα : Set α
left✝¹ : tα ⊆ univ
hfin✝ : tα.Finite
htα : univ ⊆ ⋃ x ∈ tα, U x
val✝¹ : Fintype ↑tα
tβ : Set β
left✝ : tβ ⊆ univ
hfin : tβ.Finite
htβ : univ ⊆ ⋃ y ∈ tβ, ball y ε₂
val✝ : Fintype ↑tβ
F : β → β
hF : ∀ (y : β), F y ∈ tβ ∧ dist y (F y) < ε₂
f : α →ᵇ β
hf : f ∈ A
g : α →ᵇ β
hg : g ∈ A
f_eq_g : (fun f a => ⟨F (↑f ↑a), ⋯⟩) ⟨f, hf⟩ = (fun f a => ⟨F (↑f ↑a), ⋯⟩) ⟨g, hg⟩
x x' : α
x'tα : x' ∈ tα
hx' : x ∈ U x'
⊢ dist (g x) (g x') < ε₂

Tactic:
exact (hU x').2.2 _ hx' _ (hU x').1 hg

Result:
no goals

Proof state:
case intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε

Tactic:
let ε₂ := ε₁ / 2 / 2

Result:
case intro.intro
α : Type u
β : Type v
inst✝³ : TopologicalSpace α
inst✝² : CompactSpace α
inst✝¹ : PseudoMetricSpace β
inst✝ : CompactSpace β
A : Set (α →ᵇ β)
closed : IsClosed A
H : ∀ (x₀ : α), ∀ ε > 0, ∃ U ∈ 𝓝 x₀, ∀ x ∈ U, ∀ x' ∈ U, ∀ (i : ↑A), dist (↑i x) (↑i x') < ε
ε : ℝ
ε0 : ε > 0
ε₁ : ℝ
ε₁0 : 0 < ε₁
εε₁ : ε₁ < ε
ε₂ : ℝ := ε₁ / 2 / 2
⊢ ∃ β_1 x F, ∀ (x y : ↑A), F x = F y → dist ↑x ↑y < ε