SlotAction parseSlotAction (Model model, Set<String> variables) throws Exception
	{
		String operator = "";
		if (t.getToken().equals("-") || t.getToken().equals("<") || t.getToken().equals(">")
				|| t.getToken().equals("<=") || t.getToken().equals(">="))
		{
			operator = t.getToken();
			t.advance();
		}
		Symbol slot = Symbol.get (operator+t.getToken());
		if (slot.isVariable() && !variables.contains(slot.getString()))
			model.recordWarning ("variable '" + slot.getString() + "' is not set", t);
		t.advance();
		Symbol value = Symbol.get (t.getToken());
		if (value.isVariable() && !variables.contains(value.getString()))
			model.recordWarning ("variable '" + value.getString() + "' is not set", t);
		t.advance();
		return new SlotAction (model, slot, value);
	}