new_contents: import string
  successor = [("aL", "La", False),
               ("a0", "0a", False),
               ("a" , "b" , False),
               ("Lb", "b0", False),
               ("0b", "L" , True ),
               ("b" , "L" , True ),
               (""  , "a" , False)]
  def contains(s, sub):
      return s.find(sub) != -1
  def find_rule(a, w):
      try:
          return filter(lambda (l,r,b): contains(w, l), a)[0]
      except IndexError:
          raise ValueError, "not found"
  def apply_rule((l,r,b), s):
      return s.replace(l, r, 1)
  def apply_alg(a, w):
      l,r,b = r = find_rule(a, w)
      return apply_rule(r, w), b
  def run(a, w):
      result = []
      flag = False                      # whether Halting rule was applied
      try:
          while not flag:               # Normal rule was applied
              result.append(w)
              w, flag = apply_alg(a, w) # apply a rule
          result.append(w)
      except ValueError:                # No rule was applied
          pass
      return result
  
  
subject: add markov file