public ValueNumber mergeValues(ValueNumber a, ValueNumber b) {  throw new IllegalStateException("mergeValues called on a ValueNumberFrame");
public ValueNumber mergeValues(int slot, ValueNumber mine, ValueNumber other) {                      if (mine != getValue(slot)) throw new IllegalStateException(); ValueNumber mergedValue = mergedValueList.get(slot); if (mergedValue == null && !mine.equals(other)) { mergedValue = factory.createFreshValue(); mergedValueList.set(slot, mergedValue); mine = mergedValue; } return mine;
	public ValueNumber mergeValues(ValueNumber a, ValueNumber b) {		// This method is not needed for ValueNumberFrame.		throw new IllegalStateException("mergeValues called on a ValueNumberFrame");	}