private void finish() {
		if (restricted == null) {
			JOptionPane.showMessageDialog(parent,
					"There is no one right answer in this case.", "Ambiguity",
					JOptionPane.ERROR_MESSAGE);
			return;
		}
		HashSet toAdd = new HashSet(restricted);
		toAdd.removeAll(alreadyChosen);
		Iterator it = toAdd.iterator();
		while (it.hasNext())
			addItem((Production) it.next());
	}