/-- In a space with the Besicovitch property, any set `s` can be covered with balls whose measures
add up to at most `μ s + ε`, for any positive `ε`. This works even if one restricts the set of
allowed radii around a point `x` to a set `f x` which accumulates at `0`. -/
theorem exists_closedBall_covering_tsum_measure_le (μ : Measure α) [SigmaFinite μ]
    [Measure.OuterRegular μ] {ε : ℝ≥0∞} (hε : ε ≠ 0) (f : α → Set ℝ) (s : Set α)
    (hf : ∀ x ∈ s, ∀ δ > 0, (f x ∩ Ioo 0 δ).Nonempty) :
    ∃ (t : Set α) (r : α → ℝ), t.Countable ∧ t ⊆ s ∧ (∀ x ∈ t, r x ∈ f x) ∧
      (s ⊆ ⋃ x ∈ t, closedBall x (r x)) ∧ (∑' x : t, μ (closedBall x (r x))) ≤ μ s + ε := by
  /- For the proof, first cover almost all `s` with disjoint balls thanks to the usual Besicovitch
    theorem. Taking the balls included in a well-chosen open neighborhood `u` of `s`, one may
    ensure that their measures add at most to `μ s + ε / 2`. Let `s'` be the remaining set, of
    measure `0`. Applying the other version of Besicovitch, one may cover it with at most `N`
    disjoint subfamilies. Making sure that they are all included in a neighborhood `v` of `s'` of
    measure at most `ε / (2 N)`, the sum of their measures is at most `ε / 2`,
    completing the proof. -/
  obtain ⟨u, su, u_open, μu⟩ : ∃ U, U ⊇ s ∧ IsOpen U ∧ μ U ≤ μ s + ε / 2 :=
    Set.exists_isOpen_le_add _ _
      (by
        simpa only [or_false, Ne.def, ENNReal.div_eq_zero_iff, ENNReal.two_ne_top] using hε)
  have : ∀ x ∈ s, ∃ R > 0, ball x R ⊆ u := fun x hx =>
    Metric.mem_nhds_iff.1 (u_open.mem_nhds (su hx))
  choose! R hR using this
  obtain ⟨t0, r0, t0_count, t0s, hr0, μt0, t0_disj⟩ :
    ∃ (t0 : Set α) (r0 : α → ℝ), t0.Countable ∧ t0 ⊆ s ∧
      (∀ x ∈ t0, r0 x ∈ f x ∩ Ioo 0 (R x)) ∧ μ (s \ ⋃ x ∈ t0, closedBall x (r0 x)) = 0 ∧
        t0.PairwiseDisjoint fun x => closedBall x (r0 x) :=
    exists_disjoint_closedBall_covering_ae μ f s hf R fun x hx => (hR x hx).1
  -- we have constructed an almost everywhere covering of `s` by disjoint balls. Let `s'` be the
  -- remaining set.
  let s' := s \ ⋃ x ∈ t0, closedBall x (r0 x)
  have s's : s' ⊆ s := diff_subset _ _
  obtain ⟨N, τ, hτ, H⟩ : ∃ N τ, 1 < τ ∧ IsEmpty (Besicovitch.SatelliteConfig α N τ) :=
    HasBesicovitchCovering.no_satelliteConfig
  obtain ⟨v, s'v, v_open, μv⟩ : ∃ v, v ⊇ s' ∧ IsOpen v ∧ μ v ≤ μ s' + ε / 2 / N :=
    Set.exists_isOpen_le_add _ _
      (by
        simp only [ne_eq, ENNReal.div_eq_zero_iff, hε, ENNReal.two_ne_top, or_self,
          ENNReal.nat_ne_top, not_false_eq_true])
  have : ∀ x ∈ s', ∃ r1 ∈ f x ∩ Ioo (0 : ℝ) 1, closedBall x r1 ⊆ v := by
    intro x hx
    rcases Metric.mem_nhds_iff.1 (v_open.mem_nhds (s'v hx)) with ⟨r, rpos, hr⟩
    rcases hf x (s's hx) (min r 1) (lt_min rpos zero_lt_one) with ⟨R', hR'⟩
    exact
      ⟨R', ⟨hR'.1, hR'.2.1, hR'.2.2.trans_le (min_le_right _ _)⟩,
        Subset.trans (closedBall_subset_ball (hR'.2.2.trans_le (min_le_left _ _))) hr⟩
  

Proof state:
case intro.intro.intro.intro.intro.intro.intro.intro.intro.intro.intro.intro.intro.intro.intro
α : Type u_1
inst✝⁶ : MetricSpace α
β : Type u
inst✝⁵ : SecondCountableTopology α
inst✝⁴ : MeasurableSpace α
inst✝³ : OpensMeasurableSpace α
inst✝² : HasBesicovitchCovering α
μ : Measure α
inst✝¹ : SigmaFinite μ
inst✝ : Measure.OuterRegular μ
ε : ℝ≥0∞
hε : ε ≠ 0
f : α → Set ℝ
s : Set α
hf : ∀ x ∈ s, ∀ δ > 0, Set.Nonempty (f x ∩ Ioo 0 δ)
u : Set α
su : u ⊇ s
u_open : IsOpen u
μu : ↑↑μ u ≤ ↑↑μ s + ε / 2
R : α → ℝ
hR : ∀ x ∈ s, R x > 0 ∧ ball x (R x) ⊆ u
t0 : Set α
r0 : α → ℝ
t0_count : Set.Countable t0
t0s : t0 ⊆ s
hr0 : ∀ x ∈ t0, r0 x ∈ f x ∩ Ioo 0 (R x)
μt0 : ↑↑μ (s \ ⋃ x ∈ t0, closedBall x (r0 x)) = 0
t0_disj : PairwiseDisjoint t0 fun x => closedBall x (r0 x)
s' : Set α := s \ ⋃ x ∈ t0, closedBall x (r0 x)
s's : s' ⊆ s
N : ℕ
τ : ℝ
hτ : 1 < τ
H : IsEmpty (SatelliteConfig α N τ)
v : Set α
s'v : v ⊇ s'
v_open : IsOpen v
μv : ↑↑μ v ≤ ↑↑μ s' + ε / 2 / ↑N
this : ∀ x ∈ s', ∃ r1 ∈ f x ∩ Ioo 0 1, closedBall x r1 ⊆ v
⊢ ∃ t r,
    Set.Countable t ∧
      t ⊆ s ∧
        (∀ x ∈ t, r x ∈ f x) ∧ s ⊆ ⋃ x ∈ t, closedBall x (r x) ∧ ∑' (x : ↑t), ↑↑μ (closedBall (↑x) (r ↑x)) ≤ ↑↑μ s + ε

Next tactic:
choose! r1 hr1 using this