for(Map.Entry<ValueNumber, Set<Location>> e : derefLocationSetMap.entrySet()) if (!valueNumbers.contains(e.getKey())) e.getValue().clear();
for(Iterator<ValueNumber> i = derefLocationSetMap.keySet().iterator(); i.hasNext(); ) { ValueNumber v = i.next(); if (!valueNumbers.contains(v)) { i.remove(); valueNumberSet.clear(v.getNumber()); } }
	public void retainOnlyTheseValueNumbers(Set<ValueNumber> valueNumbers) {		for(Map.Entry<ValueNumber, Set<Location>> e : derefLocationSetMap.entrySet())				if (!valueNumbers.contains(e.getKey())) e.getValue().clear();			}