simp [freshVarForm, voc, vocabOfFormula, not_or]
case box
a✝¹ : Program
a✝ : Formula
⊢ ∀ n ∈ voc (⌈a✝¹⌉a✝), n < freshVarForm (⌈a✝¹⌉a✝)
case box
a✝¹ : Program
a✝ : Formula
⊢ ∀ (n : ℕ), n ∈ vocabOfProgram a✝¹ ∨ n ∈ vocabOfFormula a✝ → n < freshVarProg a✝¹ ∨ n < freshVarForm a✝