-- Mathlib/MeasureTheory/Measure/Lebesgue/EqHaar.lean
theorem tendsto_addHaar_inter_smul_zero_of_density_zero (s : Set E) (x : E)
    (h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)) (t : Set E)
    (ht : MeasurableSet t) (h''t : μ t ≠ ∞) :
    Tendsto (fun r : ℝ => μ (s ∩ ({x} + r • t)) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 0)

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
n : ℕ
npos : 0 < n
hn : μ (t \ closedBall 0 ↑n) < ε / 2 * μ t
L : Tendsto (fun r => μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 0)
r : ℝ
hr : μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t) < ε / 2
rpos : 0 < r
I : μ (s ∩ ({x} + r • t)) ≤ μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) + μ ({x} + r • (t \ closedBall 0 ↑n))
⊢ (μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) + μ ({x} + r • (t \ closedBall 0 ↑n))) / μ ({x} + r • t) < ε / 2 + ε / 2

Tactic:
rw [ENNReal.add_div]

Result:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
n : ℕ
npos : 0 < n
hn : μ (t \ closedBall 0 ↑n) < ε / 2 * μ t
L : Tendsto (fun r => μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 0)
r : ℝ
hr : μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t) < ε / 2
rpos : 0 < r
I : μ (s ∩ ({x} + r • t)) ≤ μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) + μ ({x} + r • (t \ closedBall 0 ↑n))
⊢ μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t) + μ ({x} + r • (t \ closedBall 0 ↑n)) / μ ({x} + r • t) <
    ε / 2 + ε / 2

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
n : ℕ
npos : 0 < n
hn : μ (t \ closedBall 0 ↑n) < ε / 2 * μ t
L : Tendsto (fun r => μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 0)
r : ℝ
hr : μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t) < ε / 2
rpos : 0 < r
I : μ (s ∩ ({x} + r • t)) ≤ μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) + μ ({x} + r • (t \ closedBall 0 ↑n))
⊢ μ ({x} + r • (t \ closedBall 0 ↑n)) / μ ({x} + r • t) < ε / 2

Tactic:
rwa [addHaar_singleton_add_smul_div_singleton_add_smul μ rpos.ne',
  ENNReal.div_lt_iff (Or.inl h't) (Or.inl h''t)]

Result:
no goals

Proof state:
case h
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
n : ℕ
npos : 0 < n
hn : μ (t \ closedBall 0 ↑n) < ε / 2 * μ t
L : Tendsto (fun r => μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 0)
r : ℝ
hr : μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) / μ ({x} + r • t) < ε / 2
rpos : 0 < r
I : μ (s ∩ ({x} + r • t)) ≤ μ (s ∩ ({x} + r • (t ∩ closedBall 0 ↑n))) + μ ({x} + r • (t \ closedBall 0 ↑n))
⊢ μ (s ∩ ({x} + r • t)) / μ ({x} + r • t) < ε

Tactic:
calc
  μ (s ∩ ({x} + r • t)) / μ ({x} + r • t) ≤
      (μ (s ∩ ({x} + r • (t ∩ closedBall 0 n))) + μ ({x} + r • (t \ closedBall 0 n))) /
        μ ({x} + r • t) := by gcongr
  _ < ε / 2 + ε / 2 := by
    rw [ENNReal.add_div]
    apply ENNReal.add_lt_add hr _
    rwa [addHaar_singleton_add_smul_div_singleton_add_smul μ rpos.ne',
      ENNReal.div_lt_iff (Or.inl h't) (Or.inl h''t)]
  _ = ε := ENNReal.add_halves _

Result:
no goals

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
this : ⋂ n, t \ closedBall 0 ↑n = ∅
A : Tendsto (fun n => μ (t \ closedBall 0 ↑n)) atTop (𝓝 0)
⊢ ∃ n, 0 < n ∧ μ (t \ closedBall 0 ↑n) < ε / 2 * μ t

Tactic:
have I : 0 < ε / 2 * μ t := ENNReal.mul_pos (ENNReal.half_pos εpos.ne').ne' h't

Result:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
this : ⋂ n, t \ closedBall 0 ↑n = ∅
A : Tendsto (fun n => μ (t \ closedBall 0 ↑n)) atTop (𝓝 0)
I : 0 < ε / 2 * μ t
⊢ ∃ n, 0 < n ∧ μ (t \ closedBall 0 ↑n) < ε / 2 * μ t

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t = 0
r : ℝ
⊢ μ ({x} + r • t) = 0

Tactic:
simp only [h't, addHaar_smul, image_add_left, measure_preimage_add, singleton_add,
  mul_zero]

Result:
no goals

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
A : Tendsto (fun n => μ (t \ closedBall 0 ↑n)) atTop (𝓝 (μ (⋂ n, t \ closedBall 0 ↑n)))
⊢ ∃ n, 0 < n ∧ μ (t \ closedBall 0 ↑n) < ε / 2 * μ t

Tactic:
have : ⋂ n : ℕ, t \ closedBall 0 n = ∅ := by
  simp_rw [diff_eq, ← inter_iInter, iInter_eq_compl_iUnion_compl, compl_compl,
    iUnion_closedBall_nat, compl_univ, inter_empty]

Result:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t ≠ 0
A : Tendsto (fun n => μ (t \ closedBall 0 ↑n)) atTop (𝓝 (μ (⋂ n, t \ closedBall 0 ↑n)))
this : ⋂ n, t \ closedBall 0 ↑n = ∅
⊢ ∃ n, 0 < n ∧ μ (t \ closedBall 0 ↑n) < ε / 2 * μ t

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
s : Set E
x : E
h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t : Set E
ht : MeasurableSet t
h''t : μ t ≠ ⊤
ε : ℝ≥0∞
εpos : 0 < ε
h't : μ t = 0
r : ℝ
H : μ (s ∩ ({x} + r • t)) = 0
⊢ 0 / μ ({x} + r • t) < ε

Tactic:
simpa only [ENNReal.zero_div] using εpos

Result:
no goals