if (!frame.isValid()) return;
	private void markFrameValues(ValueNumberFrame frame) {		for (int j = 0; j < frame.getNumSlots(); ++j) {			ValueNumber value = frame.getValue(j);			int number = value.getNumber();			if (!valuesUsed.get(number)) {				discovered[number] = numValuesUsed++;				valuesUsed.set(number, true);			}		}	}