theorem extracted_formal_statement_61.{u_1, w, u} {Ω : Type u} [inst : MeasurableSpace Ω] {Z : Type w} {n : ℕ}
  {ι : Type u_1} {f : ι → Z → ℝ} [inst_1 : Countable ι] {X : Ω → Z} (hf : ∀ (i : ι), Measurable (f i ∘ X)) (σ : Signs n)
  (a : σ ∈ Finset.univ) (i : ι) (k : Fin n) (a_1 : k ∈ Finset.univ) : Measurable fun a => f i (X (a.1 k)) := sorry

State before:
case hf.hf
Ω : Type u
inst✝¹ : MeasurableSpace Ω
Z : Type w
n : ℕ
ι : Type u_1
f : ι → Z → ℝ
inst✝ : Countable ι
X : Ω → Z
hf : ∀ (i : ι), Measurable (f i ∘ X)
σ : Signs n
a✝¹ : σ ∈ Finset.univ
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: