unfold_rec4.lean:8:0: error: 1 unsolved subgoal
n : ℕ
⊢ succ (succ (succ (succ (f n)))) = sorry
unfold_rec4.lean:8:0: error: failed to add declaration 'example' to environment, value has metavariables
remark: set 'formatter.hide_full_terms' to false to see the complete term
  ?M_1