next hf hg =>
  rw [encode, decode]
  split
  next h => simp at h
  next h =>
    simp [Nat.div2_val] at h
    cases h
    simp [*]
case cons
a✝¹ a✝ : ConsExp
a_ih✝¹ : decode (encode a✝¹) = a✝¹
a_ih✝ : decode (encode a✝) = a✝
⊢ decode (encode (cons a✝¹ a✝)) = cons a✝¹ a✝
no goals