public FloatSortedSet keySet() {
   if (keys == null) keys = FloatSortedSets.synchronize(sortedMap.keySet(), sync);
   return (FloatSortedSet) keys;
 }
 public FloatSortedSet keySet() {
   if (keys == null) keys = FloatSortedSets.unmodifiable(sortedMap.keySet());
   return (FloatSortedSet) keys;
 }
 public FloatSortedSet keySet() {
   if (keys == null) keys = FloatSortedSets.singleton(key, comparator);
   return (FloatSortedSet) keys;
 }