* read operations will work correctly. To allow concurrent update operations, wrap your multimap
 * with a call to {@link Multimaps#synchronizedSortedSetMultimap}.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap">{@code Multimap}</a>.
 *
 * @author Jared Levy
 * @author Louis Wasserman