theorem tendsto_addHaar_inter_smul_one_of_density_one_aux (s : Set E) (hs : MeasurableSet s)
    (x : E) (h : Tendsto (fun r => μ (s ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 1))
    (t : Set E) (ht : MeasurableSet t) (h't : μ t ≠ 0) (h''t : μ t ≠ ∞) :
    Tendsto (fun r : ℝ => μ (s ∩ ({x} + r • t)) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 1) := by
  have I : ∀ u v, μ u ≠ 0 → μ u ≠ ∞ → MeasurableSet v →
    μ u / μ u - μ (vᶜ ∩ u) / μ u = μ (v ∩ u) / μ u := by
    intro u v uzero utop vmeas
    simp_rw [div_eq_mul_inv]
    rw [← ENNReal.sub_mul]; swap
    · simp only [uzero, ENNReal.inv_eq_top, imp_true_iff, Ne.def, not_false_iff]
    congr 1
    apply
      ENNReal.sub_eq_of_add_eq (ne_top_of_le_ne_top utop (measure_mono (inter_subset_right _ _)))
    rw [inter_comm _ u, inter_comm _ u]
    exact measure_inter_add_diff u vmeas
  have L : Tendsto (fun r => μ (sᶜ ∩ closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0) := by
    have A : Tendsto (fun r => μ (closedBall x r) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 1) := by
      apply tendsto_const_nhds.congr' _
      filter_upwards [self_mem_nhdsWithin]
      intro r hr
      rw [div_eq_mul_inv, ENNReal.mul_inv_cancel]
      · exact (measure_closedBall_pos μ _ hr).ne'
      · exact measure_closedBall_lt_top.ne
    have B := ENNReal.Tendsto.sub A h (Or.inl ENNReal.one_ne_top)
    simp only [tsub_self] at B
    apply B.congr' _
    filter_upwards [self_mem_nhdsWithin]
    rintro r (rpos : 0 < r)
    convert I (closedBall x r) sᶜ (measure_closedBall_pos μ _ rpos).ne'
      measure_closedBall_lt_top.ne hs.compl
    rw [compl_compl]
  have L' : Tendsto (fun r : ℝ => μ (sᶜ ∩ ({x} + r • t)) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 0) :=
    tendsto_addHaar_inter_smul_zero_of_density_zero μ sᶜ x L t ht h''t
  have L'' : Tendsto (fun r : ℝ => μ ({x} + r • t) / μ ({x} + r • t)) (𝓝[>] 0) (𝓝 1) := by
    apply tendsto_const_nhds.congr' _
    filter_upwards [self_mem_nhdsWithin]
    rintro r (rpos : 0 < r)
    rw [addHaar_singleton_add_smul_div_singleton_add_smul μ rpos.ne', ENNReal.div_self h't h''t]
  have := ENNReal.Tendsto.sub L'' L' (Or.inl ENNReal.one_ne_top)
  simp only [tsub_zero] at this
  apply this.congr' _
  filter_upwards [self_mem_nhdsWithin]
  

Proof state:
case h
E : Type u_1
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : MeasurableSpace E
inst✝⁵ : BorelSpace E
inst✝⁴ : FiniteDimensional ℝ E
μ : Measure E
inst✝³ : IsAddHaarMeasure μ
F : Type u_2
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
inst✝ : CompleteSpace F
s✝ s : Set E
hs : MeasurableSet s
x : E
h : Tendsto (fun r => ↑↑μ (s ∩ closedBall x r) / ↑↑μ (closedBall x r)) (𝓝[>] 0) (𝓝 1)
t : Set E
ht : MeasurableSet t
h't : ↑↑μ t ≠ 0
h''t : ↑↑μ t ≠ ⊤
I :
  ∀ (u v : Set E), ↑↑μ u ≠ 0 → ↑↑μ u ≠ ⊤ → MeasurableSet v → ↑↑μ u / ↑↑μ u - ↑↑μ (vᶜ ∩ u) / ↑↑μ u = ↑↑μ (v ∩ u) / ↑↑μ u
L : Tendsto (fun r => ↑↑μ (sᶜ ∩ closedBall x r) / ↑↑μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
L' : Tendsto (fun r => ↑↑μ (sᶜ ∩ ({x} + r • t)) / ↑↑μ ({x} + r • t)) (𝓝[>] 0) (𝓝 0)
L'' : Tendsto (fun r => ↑↑μ ({x} + r • t) / ↑↑μ ({x} + r • t)) (𝓝[>] 0) (𝓝 1)
this :
  Tendsto (fun a => ↑↑μ ({x} + a • t) / ↑↑μ ({x} + a • t) - ↑↑μ (sᶜ ∩ ({x} + a • t)) / ↑↑μ ({x} + a • t)) (𝓝[>] 0) (𝓝 1)
⊢ ∀ a ∈ Ioi 0,
    ↑↑μ ({x} + a • t) / ↑↑μ ({x} + a • t) - ↑↑μ (sᶜ ∩ ({x} + a • t)) / ↑↑μ ({x} + a • t) =
      ↑↑μ (s ∩ ({x} + a • t)) / ↑↑μ ({x} + a • t)

Next tactic:
rintro r (rpos : 0 < r)