theorem extracted_formal_statement_135.{w, v, u} {Z : Type w} {ι : Type v} {f : ι → Z → ℝ} {Ω : Type u}
  [inst : MeasurableSpace Ω] {X : Ω → Z} {μ : Measure Ω} [inst_1 : IsProbabilityMeasure μ] [inst_2 : Countable ι]
  [inst_3 : Nonempty ι] (h𝓕 : ∀ (I : ι), Measurable (f I ∘ X)) {b : ℝ} (h𝓕' : ∀ (I : ι) (z : Z), |f I z| ≤ b) {n : ℕ}
  {c : ι → ℝ} {C : ℝ} (hC : ∀ (I : ι), |c I| ≤ C) (σ : Fin (n + 1) → { x // x ∈ {-1, 1} }) (a : σ ∈ Finset.univ) (I : ι)
  (i : Fin n) (a_1 : i ∈ Finset.univ) : Measurable fun x => f I (X (x.2 i).1) - f I (X (x.2 i).2) := sorry

State before:
case left.hf.hf.hf.hf.hf
Z : Type w
ι : Type v
f : ι → Z → ℝ
Ω : Type u
inst✝³ : MeasurableSpace Ω
X : Ω → Z
μ : Measure Ω
inst✝² : IsProbabilityMeasure μ
inst✝¹ : Countable ι
inst✝ : Nonempty ι
h𝓕 : ∀ (I : ι), Measurable (f I ∘ X)
b : ℝ
h𝓕' : ∀ (I : ι) (z : Z), |f I z| ≤ b
n : ℕ
c : ι → ℝ
C : ℝ
hC : ∀ (I : ι), |c I| ≤ C
σ : Fin (n + 1) → { x // x ∈ {-1, 1} }
a✝¹ : σ ∈ Finset.univ
I : ι
i : Fin n
a✝ : i ∈ Finset.univ
⊢ Measurable fun x => f I (X (x.2 i).1) - f I (X (x.2 i).2)

Tactic: exact (measurable_sub_part h𝓕).comp measurable_snd

State after:

Relevant lemmas:
measurable_snd : ∀ {α : Type u_1} {β : Type u_2} {x : MeasurableSpace α} {x_1 : MeasurableSpace β}, Measurable Prod.snd
measurable_sub_part : ∀ {Z : Type w} {ι : Type v} {f : ι → Z → ℝ} {Ω : Type u} [inst : MeasurableSpace Ω] {X : Ω → Z}
  [inst_4 : Countable ι],
  (∀ (I : ι), Measurable (f I ∘ X)) →
    ∀ {n : ℕ} {I : ι} {i : Fin n}, Measurable fun ω => f I (X (ω i).1) - f I (X (ω i).2)