public K lastKey() {
   return sortedMap.lastKey();
 }
 public Reference2DoubleSortedMap<K> tailMap(final K from) {
   return new UnmodifiableSortedMap<K>(sortedMap.tailMap(from));
 }
 public K firstKey() {
   return sortedMap.firstKey();
 }
 public Reference2DoubleSortedMap<K> subMap(final K from, final K to) {
   return new UnmodifiableSortedMap<K>(sortedMap.subMap(from, to));
 }
 public Reference2DoubleSortedMap<K> headMap(final K to) {
   return new UnmodifiableSortedMap<K>(sortedMap.headMap(to));
 }
 public ObjectSortedSet<Reference2DoubleMap.Entry<K>> reference2DoubleEntrySet() {
   if (entries == null)
     entries = ObjectSortedSets.unmodifiable(sortedMap.reference2DoubleEntrySet());
   return (ObjectSortedSet<Reference2DoubleMap.Entry<K>>) entries;
 }
 public ReferenceSortedSet<K> keySet() {
   if (keys == null) keys = ReferenceSortedSets.unmodifiable(sortedMap.keySet());
   return (ReferenceSortedSet<K>) keys;
 }
 public K lastKey() {
   synchronized (sync) {
     return sortedMap.lastKey();
   }
 }
 public Comparator<? super K> comparator() {
   return sortedMap.comparator();
 }
 public Reference2DoubleSortedMap<K> tailMap(final K from) {
   return new SynchronizedSortedMap<K>(sortedMap.tailMap(from), sync);
 }
 public K firstKey() {
   synchronized (sync) {
     return sortedMap.firstKey();
   }
 }
 public Reference2DoubleSortedMap<K> headMap(final K to) {
   return new SynchronizedSortedMap<K>(sortedMap.headMap(to), sync);
 }
 public Reference2DoubleSortedMap<K> subMap(final K from, final K to) {
   return new SynchronizedSortedMap<K>(sortedMap.subMap(from, to), sync);
 }
 public ReferenceSortedSet<K> keySet() {
   if (keys == null) keys = ReferenceSortedSets.synchronize(sortedMap.keySet(), sync);
   return (ReferenceSortedSet<K>) keys;
 }
 public ObjectSortedSet<Reference2DoubleMap.Entry<K>> reference2DoubleEntrySet() {
   if (entries == null)
     entries = ObjectSortedSets.synchronize(sortedMap.reference2DoubleEntrySet(), sync);
   return (ObjectSortedSet<Reference2DoubleMap.Entry<K>>) entries;
 }
 public Comparator<? super K> comparator() {
   synchronized (sync) {
     return sortedMap.comparator();
   }
 }