#!/usr/bin/env python

import sys

productions = set()

puzzle = 'MI';

def print_rules():

print('')

print('Rule I: If you possess a string whose last letter is \'I\' you can add')

print(' on a \'U\' at the end.')

print('Rule II: Suppose you have "Mx", you may add "Mxx" to your collection.')

print('Rule III: If "III" occurs in one of the strings in your collection you may')

print(' make a new string with "U" in place of "III".')

print('Rule IV: If "UU" occurs inside one of your strings, you can drop it.')

print('')

def print_help():

print('')

print('Following commands are available:')

print(' h show this list of commands')

print(' q quit')

print(' s to show the rules')

print(' r start over')

print(' p print all strings you produced')

print(' 1 apply rule I if possible')

print(' 2 apply rule II if possible')

print(' 3 apply rule III if possible')

print(' 4 apply rule IV if possible')

print('')

print('You are about to enjoy some time experimenting with a formal system called')

print('MIU-system. It\'s words consist only of the letters \'M\', \'I\' and \'U\'')

print('and there are four rules to apply to those words/strings:')

print_rules()

print('You will be given the string "MI", which you must transform to "MU" using')

print('the above rules.')

print_help()

while puzzle is not 'MU':

cmd = input('Enter a character and press enter: ')

if cmd is 'h':

print_help()

elif cmd is 'q':

sys.exit(0)

elif cmd is 's':

print_rules()

elif cmd is 'p':

print('')

print('Strings you produced:' + ' ').join(item for item in productions)

print('')

else:

if cmd is 'r':

puzzle = 'MI'

elif cmd is '1':

if puzzle[-1] is 'I':

puzzle += 'U'

elif cmd is '2':

puzzle += puzzle[1:]

elif cmd is '3':

puzzle = puzzle.replace('III', 'U')

elif cmd is '4':

puzzle = puzzle.replace('UU', '')

else:

print('Sorry, I did not understand that command. Enter \'h\' for a list of commands.')

continue

print('You produced the string "' + puzzle + '"')

productions.add(puzzle)

print('Congratulations, you solved the MU-puzzle!')