code: public CollectionValuedMap<K, V> deltaClone() {
      CollectionValuedMap<K, V> result = new CollectionValuedMap<K, V>(null, cf, true);
      result.map = new DeltaMap<K, Collection<V>>(this.map);
      return result;
    }
docs: Creates a "delta clone" of this Map, where only the differences are
  represented.