theorem tendsto_addHaar_inter_smul_zero_of_density_zero_aux1 (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)
    (u : Set E) (h'u : μ u ≠ 0) (t_bound : t ⊆ closedBall 0 1) :
    Tendsto (fun r : ℝ => μ (s ∩ ({x} + r • t)) / μ ({x} + r • u)) (𝓝[>] 0) (𝓝 0) := by
  have A : Tendsto (fun r : ℝ => μ (s ∩ ({x} + r • t)) / μ (closedBall x r)) (𝓝[>] 0) (𝓝 0) := by
    apply
      tendsto_of_tendsto_of_tendsto_of_le_of_le' tendsto_const_nhds h
        (eventually_of_forall fun b => zero_le _)
    filter_upwards [self_mem_nhdsWithin]
    rintro r (rpos : 0 < r)
    apply mul_le_mul_right' (measure_mono (inter_subset_inter_right _ _)) _
    intro y hy
    have : y - x ∈ r • closedBall (0 : E) 1 := by
      apply smul_set_mono t_bound
      simpa [neg_add_eq_sub] using hy
    simpa only [smul_closedBall _ _ zero_le_one, Real.norm_of_nonneg rpos.le,
      mem_closedBall_iff_norm, mul_one, sub_zero, smul_zero]
  have B :
    Tendsto (fun r : ℝ => μ (closedBall x r) / μ ({x} + r • u)) (𝓝[>] 0)
      (𝓝 (μ (closedBall x 1) / μ ({x} + u))) := by
    apply tendsto_const_nhds.congr' _
    filter_upwards [self_mem_nhdsWithin]
    rintro r (rpos : 0 < r)
    have : closedBall x r = {x} + r • closedBall (0 : E) 1 := by
      simp only [_root_.smul_closedBall, Real.norm_of_nonneg rpos.le, zero_le_one, add_zero,
        mul_one, singleton_add_closedBall, smul_zero]
    simp only [this, addHaar_singleton_add_smul_div_singleton_add_smul μ rpos.ne']
    simp only [addHaar_closedBall_center, image_add_left, measure_preimage_add, singleton_add]
  have C : Tendsto (fun r : ℝ =>
        μ (s ∩ ({x} + r • t)) / μ (closedBall x r) * (μ (closedBall x r) / μ ({x} + r • u)))
      (𝓝[>] 0) (𝓝 (0 * (μ (closedBall x 1) / μ ({x} + u)))) := by
    apply ENNReal.Tendsto.mul A _ B (Or.inr ENNReal.zero_ne_top)
    simp only [ne_eq, not_true, singleton_add, image_add_left, measure_preimage_add, false_or,
      ENNReal.div_eq_top, h'u, false_or_iff, not_and, and_false_iff]
    intro aux
    exact (measure_closedBall_lt_top.ne aux).elim
    -- Porting note: it used to be enough to pass `measure_closedBall_lt_top.ne` to `simp`
    -- and avoid the `intro; exact` dance.
  simp only [zero_mul] at C
  apply C.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
x : E
h : Tendsto (fun r => ↑↑μ (s ∩ closedBall x r) / ↑↑μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
t u : Set E
h'u : ↑↑μ u ≠ 0
t_bound : t ⊆ closedBall 0 1
A : Tendsto (fun r => ↑↑μ (s ∩ ({x} + r • t)) / ↑↑μ (closedBall x r)) (𝓝[>] 0) (𝓝 0)
B : Tendsto (fun r => ↑↑μ (closedBall x r) / ↑↑μ ({x} + r • u)) (𝓝[>] 0) (𝓝 (↑↑μ (closedBall x 1) / ↑↑μ ({x} + u)))
C :
  Tendsto (fun r => ↑↑μ (s ∩ ({x} + r • t)) / ↑↑μ (closedBall x r) * (↑↑μ (closedBall x r) / ↑↑μ ({x} + r • u)))
    (𝓝[>] 0) (𝓝 0)
⊢ ∀ a ∈ Ioi 0,
    ↑↑μ (s ∩ ({x} + a • t)) / ↑↑μ (closedBall x a) * (↑↑μ (closedBall x a) / ↑↑μ ({x} + a • u)) =
      ↑↑μ (s ∩ ({x} + a • t)) / ↑↑μ ({x} + a • u)

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