* order to guarantee serial access, it is critical that <b>all</b> access to the backing
   * navigable set is accomplished through the returned navigable set (or its views).
   *
   * <p>It is imperative that the user manually synchronize on the returned sorted set when
   * iterating over it or any of its {@code descendingSet}, {@code subSet}, {@code headSet}, or
   * {@code tailSet} views.
   *
   * <pre>{@code

   * TreeMultimap#create(Comparator, Comparator)} won't suffice.
   *
   * <p>Note: the multimap assumes complete ownership over of {@code map} and the collections
   * returned by {@code factory}. Those objects should not be manually updated and they should not
   * use soft, weak, or phantom references.
   *
   * @param map place to store the mapping from each key to its corresponding values

   * serial access, it is critical that <b>all</b> access to the backing bimap is accomplished
   * through the returned bimap.
   *
   * <p>It is imperative that the user manually synchronize on the returned map when accessing any
   * of its collection views:
   *
   * <pre>{@code
   * BiMap<Long, String> map = Maps.synchronizedBiMap(
   *     HashBiMap.<Long, String>create());