public Set getWantedNonterminals() {
		Method [] methods = getClass().getMethods();
		Set set = new HashSet(methods.length);

		for (int i = 0; i < methods.length; i++)	{
			Method m = methods[i];
			Class [] argClasses = m.getParameterTypes();

			if (m.getReturnType().equals(void.class) && argClasses.length == 1 && argClasses[0].equals(ResultTree.class))	{
				String name = m.getName();
				set.add(name);
			}
		}
		return set;
	}