func_code: def index(str, letter, pos):
      if pos == len(str):
          return 'False'
      elif str[pos] == letter:
          return 'True'
      else:
          return search(str, letter, pos + 1)
  
  
  def search(str, letter):
      i = 0
      while i < len(str):
          if str[i] == letter:
              return 'True'
          i = i + 1
      return 'False'