@SafeVarargs
  public static <T extends @Nullable Object> Stream<T> concat(Stream<? extends T>... streams) {
    // TODO(lowasser): consider an implementation that can support SUBSIZED
    boolean isParallel = false;
    int characteristics = Spliterator.ORDERED | Spliterator.SIZED | Spliterator.NONNULL;
    long estimatedSize = 0L;
    ImmutableList.Builder<Spliterator<? extends T>> splitrsBuilder =

   * advice in {@link #concat(Iterable...)}.
   *
   * @since 20.0
   */
  public static <T extends @Nullable Object> FluentIterable<T> concat(
      Iterable<? extends T> a,
      Iterable<? extends T> b,
      Iterable<? extends T> c,
      Iterable<? extends T> d) {
    return concatNoDefensiveCopy(a, b, c, d);
  }

  /**

   * advice in {@link #concat(Iterable...)}.
   *
   * @since 20.0
   */
  public static <T extends @Nullable Object> FluentIterable<T> concat(
      Iterable<? extends T> a,
      Iterable<? extends T> b,
      Iterable<? extends T> c,
      Iterable<? extends T> d) {
    return concatNoDefensiveCopy(a, b, c, d);
  }

  /**

     * @return a new instance of {@link ConcurrentHashMap}
     * @see ConcurrentHashMap#ConcurrentHashMap(Map)
     */
    public static <K, V> ConcurrentHashMap<K, V> newConcurrentHashMap(final Map<? extends K, ? extends V> m) {
        return new ConcurrentHashMap<>(m);
    }

    /**
     * Creates and returns a new instance of {@link ConcurrentLinkedQueue}.
     *

    }

    @Override
    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
        throws InterruptedException {
      throw new UnsupportedOperationException();
    }

    @Override
    public <T> List<Future<T>> invokeAll(
        Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
        throws InterruptedException {

     */
    @CanIgnoreReturnValue
    @Override
    public Builder<E> addAll(Iterable<? extends E> elements) {
      if (elements instanceof Multiset) {
        Multiset<? extends E> multiset = (Multiset<? extends E>) elements;
        multiset.forEachEntry((e, n) -> contents.add(checkNotNull(e), n));
      } else {
        super.addAll(elements);
      }

 *
 * @author Mike Bostock
 * @since 2.0
 */
@GwtCompatible
@J2ktIncompatible
public final class EnumBiMap<K extends Enum<K>, V extends Enum<V>> extends AbstractBiMap<K, V> {
  /*
   * J2CL's EnumMap does not need the Class instance, so we can use Object.class instead. (Or we

      return mapGenerator;
    }
  }

  public static class MapSortedKeySetGenerator<
          K extends @Nullable Object, V extends @Nullable Object>
      extends MapKeySetGenerator<K, V> implements TestSortedSetGenerator<K> {
    private final TestSortedMapGenerator<K, V> delegate;

    public MapSortedKeySetGenerator(

   */
  public static <F extends @Nullable Object, T extends @Nullable Object> Supplier<T> compose(
      Function<? super F, T> function, Supplier<F> supplier) {
    return new SupplierComposition<>(function, supplier);
  }

  private static final class SupplierComposition<
          F extends @Nullable Object, T extends @Nullable Object>
      implements Supplier<T>, Serializable {

    CHECKED(IOException.class),
    UNCHECKED(RuntimeException.class);

    final Class<? extends Exception> exceptionType;

    ExceptionType(Class<? extends Exception> exceptionType) {
      this.exceptionType = exceptionType;
    }
  }

  private static final ImmutableSet<Class<? extends Exception>> OTHER_EXCEPTION_TYPES =
      ImmutableSet.of(
          BackingStoreException.class,