docs: def main():
      """
      Testing function for PDA - DFA Diff Operation
      """
      if len(argv) < 2:
          print 'Usage: '
          print '         Get A String              %s CFG_fileA FST_fileB' % argv[0]
          return
  
      alphabet = createalphabet()
  
      cfgtopda = CfgPDA(alphabet)
      print '* Parsing Grammar:',
      mma = cfgtopda.yyparse(argv[1])
      print 'OK'
  
      flex_a = Flexparser(alphabet)
      print '* Parsing Regex:',
      mmb = flex_a.yyparse(argv[2])
      print mmb
      print 'OK'
      print '* Minimize Automaton:',
      mmb.minimize()
      print 'OK'
      print mmb
      print '* Diff:',
      ops = PdaDiff(mma, mmb, alphabet)
      mmc = ops.diff()
      print 'OK'
      print '* Get String:',
      print ops.get_string()