import static com.google.common.collect.Multimaps.synchronizedMultimap;
import static com.google.common.collect.Multimaps.synchronizedSetMultimap;
import static com.google.common.collect.Multimaps.synchronizedSortedSetMultimap;
import static com.google.common.collect.ReflectionFreeAssertThrows.assertThrows;
import static com.google.common.collect.Sets.newHashSet;
import static com.google.common.collect.testing.Helpers.nefariousMapEntry;

 * 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

          SortedSetMultimap<K, V> multimap, @Nullable Object mutex) {
    if (multimap instanceof SynchronizedSortedSetMultimap) {
      return multimap;
    }
    return new SynchronizedSortedSetMultimap<>(multimap, mutex);
  }

  static final class SynchronizedSortedSetMultimap<
          K extends @Nullable Object, V extends @Nullable Object>

          SortedSetMultimap<K, V> multimap, @Nullable Object mutex) {
    if (multimap instanceof SynchronizedSortedSetMultimap) {
      return multimap;
    }
    return new SynchronizedSortedSetMultimap<>(multimap, mutex);
  }

  static final class SynchronizedSortedSetMultimap<
          K extends @Nullable Object, V extends @Nullable Object>

   * {@code map} and the instances generated by {@code factory} are. Concurrent read operations will
   * work correctly. To allow concurrent update operations, wrap the multimap with a call to {@link
   * #synchronizedSortedSetMultimap}.
   *
   * <p>Call this method only when the simpler methods {@link TreeMultimap#create()} and {@link
   * TreeMultimap#create(Comparator, Comparator)} won't suffice.
   *