public PairList<String,String> createBinaryChoices(String[] S) 
		{
			if(choices != null)
				return choices;
			choices = createChoices(new XVector<String>(S).elements());
			for(int i=0;i<choices.size();i++)
			{
				if(i==0)
					choices.get(i).first =Integer.toString(0);
				else
					choices.get(i).first = Integer.toString(1<<(i-1));
			}
			return choices;
		}