theorem extracted_formal_statement_1.{w, v, u} {n : ℕ} {Ω : Type u} [inst : MeasurableSpace Ω] {ι : Type v} {𝒳 : Type w}
  {μ : Measure Ω} {f : ι → 𝒳 → ℝ} [inst_1 : Nonempty ι] [inst_2 : Countable ι] [inst_3 : IsProbabilityMeasure μ]
  (hn : 0 < n) (X : Ω → 𝒳) (hf : ∀ (i : ι), Measurable (f i ∘ X)) {b : ℝ} (hb : 0 ≤ b)
  (hf' : ∀ (i : ι) (x : 𝒳), |f i x| ≤ b)
  (h_original_goal :
    (↑n * ∫ (x : Fin n → Ω), (fun ω => uniformDeviation n f μ X (X ∘ ω)) x ∂Measure.pi fun x => μ) =
      ∫ (x : Fin n → Ω),
        (fun ω => ⨆ i, |∑ k, f i (X (ω k)) - n • ∫ (x : Ω), (fun ω' => f i (X ω')) x ∂μ|) x ∂Measure.pi fun x => μ) :
  (∫ (a : Fin n → Ω), ↑n * uniformDeviation n f μ X (X ∘ a) ∂Measure.pi fun x => μ) =
    ∫ (x : Fin n → Ω),
      (fun ω => ⨆ i, |∑ k, f i (X (ω k)) - n • ∫ (x : Ω), (fun ω' => f i (X ω')) x ∂μ|)
        x ∂Measure.pi fun x => μ := sorry

State before:
case h.e'_3
n : ℕ
Ω : Type u
inst✝³ : MeasurableSpace Ω
ι : Type v
𝒳 : Type w
μ : Measure Ω
f : ι → 𝒳 → ℝ
inst✝² : Nonempty ι
inst✝¹ : Countable ι
inst✝ : IsProbabilityMeasure μ
hn : 0 < n
X : Ω → 𝒳
hf : ∀ (i : ι), Measurable (f i ∘ X)
b : ℝ
hb : 0 ≤ b
hf' : ∀ (i : ι) (x : 𝒳), |f i x| ≤ b
⊢ (↑n * ∫ (x : Fin n → Ω), (fun ω => uniformDeviation n f μ X (X ∘ ω)) x ∂Measure.pi fun x => μ) =
    ∫ (x : Fin n → Ω),
      (fun ω => ⨆ i, |∑ k, f i (X (ω k)) - n • ∫ (x : Ω), (fun ω' => f i (X ω')) x ∂μ|) x ∂Measure.pi fun x => μ

Tactic: rw [← integral_mul_left]

State after:
[case h.e'_3
 n : ℕ
 Ω : Type u
 inst✝³ : MeasurableSpace Ω
 ι : Type v
 𝒳 : Type w
 μ : Measure Ω
 f : ι → 𝒳 → ℝ
 inst✝² : Nonempty ι
 inst✝¹ : Countable ι
 inst✝ : IsProbabilityMeasure μ
 hn : 0 < n
 X : Ω → 𝒳
 hf : ∀ (i : ι), Measurable (f i ∘ X)
 b : ℝ
 hb : 0 ≤ b
 hf' : ∀ (i : ι) (x : 𝒳), |f i x| ≤ b
 ⊢ (∫ (a : Fin n → Ω), ↑n * uniformDeviation n f μ X (X ∘ a) ∂Measure.pi fun x => μ) =
     ∫ (x : Fin n → Ω),
       (fun ω => ⨆ i, |∑ k, f i (X (ω k)) - n • ∫ (x : Ω), (fun ω' => f i (X ω')) x ∂μ|) x ∂Measure.pi fun x => μ]

Relevant lemmas:
MeasureTheory.integral_mul_left : ∀ {α : Type u_1} {m : MeasurableSpace α} {μ : Measure α} {L : Type u_6}
  [inst : RCLike L] (r : L) (f : α → L), ∫ (a : α), r * f a ∂μ = r * ∫ (a : α), f a ∂μ