theorem extracted_formal_statement_306.{u_1, w, u} {Ω : Type u} [inst : MeasurableSpace Ω] {Z : Type w} {n : ℕ}
  {ι : Type u_1} {f : ι → Z → ℝ} {μ : Measure Ω} [inst_1 : IsProbabilityMeasure μ] {X : Ω → Z} [inst_2 : Nonempty ι]
  [inst_3 : Countable ι] (hf : ∀ (i : ι), Measurable (f i ∘ X)) {b : ℝ} (hf' : ∀ (i : ι) (z : Z), |f i z| ≤ b) (i : ι)
  (k : Fin n) (a : k ∈ Finset.univ) : Measurable fun a => f i (X (a.1 k)) := sorry

State before:
case refine_1.hf.hf.hf.hf.hf.hg
Ω : Type u
inst✝¹ : MeasurableSpace Ω
Z : Type w
n : ℕ
ι : Type u_1
f : ι → Z → ℝ
μ : Measure Ω
inst✝ : IsProbabilityMeasure μ
X : Ω → Z
inst_2 : Nonempty ι
inst_3 : Countable ι
hf : ∀ (i : ι), Measurable (f i ∘ X)
b : ℝ
hf' : ∀ (i : ι) (z : Z), |f i z| ≤ b
i : ι
k : Fin n
a✝ : k ∈ Finset.univ
⊢ Measurable fun a => f i (X (a.1 k))

Tactic: apply (hf i).comp measurable_fst.eval

State after:

Relevant lemmas: