public static Set getCompleteUsefulVariableSet(Grammar grammar) {
		Set set = getNewUsefulVariableSet();
		while (areMoreVariablesThatBelongInUsefulVariableSet(grammar, set)) {
			String variable = getVariableThatBelongsInUsefulVariableSet(
					grammar, set);
			addToUsefulVariableSet(variable, set);
		}
		return set;
	}