-- Mathlib/Topology/MetricSpace/Completion.lean
theorem mem_uniformity_dist (s : Set (Completion α × Completion α)) :
    s ∈ 𝓤 (Completion α) ↔ ∃ ε > 0, ∀ {a b}, dist a b < ε → (a, b) ∈ s

Proof state:
case refine_1
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
hs : s ∈ 𝓤 (Completion α)
t : Set (Completion α × Completion α)
ht : t ∈ 𝓤 (Completion α)
tclosed : IsClosed t
ts : t ⊆ s
A : {x | (↑x.1, ↑x.2) ∈ t} ∈ 𝓤 α
ε : ℝ
εpos : ε > 0
hε : ∀ ⦃a b : α⦄, dist a b < ε → (a, b) ∈ {x | (↑x.1, ↑x.2) ∈ t}
x y : Completion α
hxy : dist x y < ε
this : {x | ε ≤ dist x.1 x.2 ∨ (x.1, x.2) ∈ t} = {p | ε ≤ dist p.1 p.2} ∪ t
⊢ IsClosed ({p | ε ≤ dist p.1 p.2} ∪ t)

Tactic:
apply IsClosed.union _ tclosed

Result:
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
hs : s ∈ 𝓤 (Completion α)
t : Set (Completion α × Completion α)
ht : t ∈ 𝓤 (Completion α)
tclosed : IsClosed t
ts : t ⊆ s
A : {x | (↑x.1, ↑x.2) ∈ t} ∈ 𝓤 α
ε : ℝ
εpos : ε > 0
hε : ∀ ⦃a b : α⦄, dist a b < ε → (a, b) ∈ {x | (↑x.1, ↑x.2) ∈ t}
x y : Completion α
hxy : dist x y < ε
this : {x | ε ≤ dist x.1 x.2 ∨ (x.1, x.2) ∈ t} = {p | ε ≤ dist p.1 p.2} ∪ t
⊢ IsClosed {p | ε ≤ dist p.1 p.2}

Proof state:
case mpr.intro.intro.intro.intro.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this : r ∈ 𝓤 ℝ
t1 : Set (Completion α × Completion α)
ht1 : t1 ∈ 𝓤 (Completion α)
t2 : Set (Completion α × Completion α)
ht2 : t2 ∈ 𝓤 (Completion α)
ht : t1 ×ˢ t2 ⊆ (fun p => ((p.1.1, p.2.1), p.1.2, p.2.2)) ⁻¹' {x | (dist x.1.1 x.1.2, dist x.2.1 x.2.2) ∈ r}
⊢ t1 ⊆ s

Tactic:
have A : ∀ a b : Completion α, (a, b) ∈ t1 → dist a b < ε := by
  intro a b hab
  have : ((a, b), (a, a)) ∈ t1 ×ˢ t2 := ⟨hab, refl_mem_uniformity ht2⟩
  have I := ht this
  simp? [r, Completion.dist_self, Real.dist_eq, Completion.dist_comm] at I says
    simp only [Real.dist_eq, mem_setOf_eq, preimage_setOf_eq, Completion.dist_self,
      Completion.dist_comm, zero_sub, abs_neg, r] at I
  exact lt_of_le_of_lt (le_abs_self _) I

Result:
case mpr.intro.intro.intro.intro.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this : r ∈ 𝓤 ℝ
t1 : Set (Completion α × Completion α)
ht1 : t1 ∈ 𝓤 (Completion α)
t2 : Set (Completion α × Completion α)
ht2 : t2 ∈ 𝓤 (Completion α)
ht : t1 ×ˢ t2 ⊆ (fun p => ((p.1.1, p.2.1), p.1.2, p.2.2)) ⁻¹' {x | (dist x.1.1 x.1.2, dist x.2.1 x.2.2) ∈ r}
A : ∀ (a b : Completion α), (a, b) ∈ t1 → dist a b < ε
⊢ t1 ⊆ s

Proof state:
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this✝ : r ∈ 𝓤 ℝ
t1 : Set (Completion α × Completion α)
ht1 : t1 ∈ 𝓤 (Completion α)
t2 : Set (Completion α × Completion α)
ht2 : t2 ∈ 𝓤 (Completion α)
ht : t1 ×ˢ t2 ⊆ (fun p => ((p.1.1, p.2.1), p.1.2, p.2.2)) ⁻¹' {x | (dist x.1.1 x.1.2, dist x.2.1 x.2.2) ∈ r}
a b : Completion α
hab : (a, b) ∈ t1
this : ((a, b), a, a) ∈ t1 ×ˢ t2
I : |dist a b| < ε
⊢ dist a b < ε

Tactic:
exact lt_of_le_of_lt (le_abs_self _) I

Result:
no goals

Proof state:
case mp.intro.intro.intro.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
hs : s ∈ 𝓤 (Completion α)
t : Set (Completion α × Completion α)
ht : t ∈ 𝓤 (Completion α)
tclosed : IsClosed t
ts : t ⊆ s
A : {x | (↑x.1, ↑x.2) ∈ t} ∈ 𝓤 α
ε : ℝ
εpos : ε > 0
hε : ∀ ⦃a b : α⦄, dist a b < ε → (a, b) ∈ {x | (↑x.1, ↑x.2) ∈ t}
x y : Completion α
hxy : dist x y < ε
this : (x, y) ∈ t
⊢ (x, y) ∈ s

Tactic:
exact ts this

Result:
no goals

Proof state:
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this : r ∈ 𝓤 ℝ
t1 : Set (Completion α × Completion α)
ht1 : t1 ∈ 𝓤 (Completion α)
t2 : Set (Completion α × Completion α)
ht2 : t2 ∈ 𝓤 (Completion α)
ht : t1 ×ˢ t2 ⊆ (fun p => ((p.1.1, p.2.1), p.1.2, p.2.2)) ⁻¹' {x | (dist x.1.1 x.1.2, dist x.2.1 x.2.2) ∈ r}
⊢ ∀ (a b : Completion α), (a, b) ∈ t1 → dist a b < ε

Tactic:
intro a b hab

Result:
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this : r ∈ 𝓤 ℝ
t1 : Set (Completion α × Completion α)
ht1 : t1 ∈ 𝓤 (Completion α)
t2 : Set (Completion α × Completion α)
ht2 : t2 ∈ 𝓤 (Completion α)
ht : t1 ×ˢ t2 ⊆ (fun p => ((p.1.1, p.2.1), p.1.2, p.2.2)) ⁻¹' {x | (dist x.1.1 x.1.2, dist x.2.1 x.2.2) ∈ r}
a b : Completion α
hab : (a, b) ∈ t1
⊢ dist a b < ε

Proof state:
case mpr
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
⊢ (∃ ε > 0, ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s) → s ∈ 𝓤 (Completion α)

Tactic:
rintro ⟨ε, εpos, hε⟩

Result:
case mpr.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
⊢ s ∈ 𝓤 (Completion α)

Proof state:
case mpr.intro.intro.intro.intro.intro.intro.mk
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this✝ : r ∈ 𝓤 ℝ
t1 : Set (Completion α × Completion α)
ht1 : t1 ∈ 𝓤 (Completion α)
t2 : Set (Completion α × Completion α)
ht2 : t2 ∈ 𝓤 (Completion α)
ht : t1 ×ˢ t2 ⊆ (fun p => ((p.1.1, p.2.1), p.1.2, p.2.2)) ⁻¹' {x | (dist x.1.1 x.1.2, dist x.2.1 x.2.2) ∈ r}
A : ∀ (a b : Completion α), (a, b) ∈ t1 → dist a b < ε
a b : Completion α
hp : (a, b) ∈ t1
this : dist a b < ε
⊢ (a, b) ∈ s

Tactic:
exact hε this

Result:
no goals

Proof state:
case mp.intro.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
hs : s ∈ 𝓤 (Completion α)
t : Set (Completion α × Completion α)
ht : t ∈ 𝓤 (Completion α)
tclosed : IsClosed t
ts : t ⊆ s
A : {x | (↑x.1, ↑x.2) ∈ t} ∈ 𝓤 α
⊢ ∃ ε > 0, ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s

Tactic:
rcases mem_uniformity_dist.1 A with ⟨ε, εpos, hε⟩

Result:
case mp.intro.intro.intro.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
hs : s ∈ 𝓤 (Completion α)
t : Set (Completion α × Completion α)
ht : t ∈ 𝓤 (Completion α)
tclosed : IsClosed t
ts : t ⊆ s
A : {x | (↑x.1, ↑x.2) ∈ t} ∈ 𝓤 α
ε : ℝ
εpos : ε > 0
hε : ∀ ⦃a b : α⦄, dist a b < ε → (a, b) ∈ {x | (↑x.1, ↑x.2) ∈ t}
⊢ ∃ ε > 0, ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s

Proof state:
case mpr.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this : r ∈ 𝓤 ℝ
⊢ s ∈ 𝓤 (Completion α)

Tactic:
have T := uniformContinuous_def.1 (@Completion.uniformContinuous_dist α _) r this

Result:
case mpr.intro.intro
α : Type u
inst✝ : PseudoMetricSpace α
s : Set (Completion α × Completion α)
ε : ℝ
εpos : ε > 0
hε : ∀ {a b : Completion α}, dist a b < ε → (a, b) ∈ s
r : Set (ℝ × ℝ) := {p | dist p.1 p.2 < ε}
this : r ∈ 𝓤 ℝ
T : {x | (dist x.1.1 x.1.2, dist x.2.1 x.2.2) ∈ r} ∈ 𝓤 (Completion α × Completion α)
⊢ s ∈ 𝓤 (Completion α)