func_code: def search(string, letter, pos):
      if pos == len(string):
          return False
      elif string[pos] == letter:
          return True
      else:
          search(string, letter, pos + 1)
annotation: def search(string, letter):
      if len(string) == 0:
          return False
      elif string[0] == letter:
          return True
      else:
          return search(string[1:], letter)
  