case EMPTY: return "empty()";
	public final static String display(int cardinality) {		switch(cardinality) {			case EXACTLY_ONE:				return ""; 			case ONE_OR_MORE:				return "+";			case ZERO_OR_MORE:				return "*";			case ZERO_OR_ONE:				return "?";			default:				// impossible				throw new IllegalArgumentException("unknown cardinality: " + cardinality);		}	}