simp [voc,vocabOfProgram,vocabOfListFormula] at *
case right
x : ℕ
ρ φ : Formula
F : List Formula
nonOcc : x ∉ voc (φ :: F)
⊢ x ∉ voc F
case right
x : ℕ
ρ φ : Formula
F : List Formula
nonOcc : x ∉ vocabOfFormula φ ∧ ∀ x_1 ∈ F, x ∉ vocabOfFormula x_1
⊢ ∀ x_1 ∈ F, x ∉ vocabOfFormula x_1