new TreeMap<CollapsedPropertyKey, List<Permutation>>();
// This loop creates the equivalence sets
for (Iterator<Permutation> it = permutations.iterator(); it.hasNext();) {
Permutation entry = it.next();
CollapsedPropertyKey key = new CollapsedPropertyKey(entry);
List<Permutation> equivalenceSet = mergedByCollapsedProperties.get(key);
if (equivalenceSet == null) {
equivalenceSet = Lists.create();
} else {