text: def enumerate_states(n_states, state_len, state, results):
  
      if n_states > 0:
  
          for sym in ('x', 'o', '_'):
              enumerate_states(n_states - 1, state_len, state + sym, results)
  
      if len(state) == state_len:
          results.append(state)
  
  
  state_len = 9
  results = []
  enumerate_states(state_len, state_len, '', results)
  print('done')
  
  