* is the only one in use, but if we encounter nested concatenations, we start a deque of
     * meta-iterators rather than letting the nesting get arbitrarily deep.  This keeps each
     * operation O(1).
     */

    private @Nullable Iterator<? extends Iterator<? extends T>> topMetaIterator;

    // Only becomes nonnull if we encounter nested concatenations.

     * is the only one in use, but if we encounter nested concatenations, we start a deque of
     * meta-iterators rather than letting the nesting get arbitrarily deep.  This keeps each
     * operation O(1).
     */

    private @Nullable Iterator<? extends Iterator<? extends T>> topMetaIterator;

    // Only becomes nonnull if we encounter nested concatenations.

   * {@code Supplier}, whose elements are the result of applying {@code elementFunction} to the
   * inputs, with counts equal to the result of applying {@code countFunction} to the inputs.
   * Elements are added in encounter order.
   *
   * <p>If the mapped elements contain duplicates (according to {@link Object#equals}), the element
   * will be added more than once, with the count summed over all appearances of the element.
   *

   * {@code Supplier}, whose elements are the result of applying {@code elementFunction} to the
   * inputs, with counts equal to the result of applying {@code countFunction} to the inputs.
   * Elements are added in encounter order.
   *
   * <p>If the mapped elements contain duplicates (according to {@link Object#equals}), the element
   * will be added more than once, with the count summed over all appearances of the element.
   *

   *
   * For convertAll, I haven't looked as closely at *how* much existing users benefit, so we should
   * keep an eye out for problems that new users encounter. Note also that convertAll could support
   * both use cases by using @PolyNull. (By contrast, we can't use @PolyNull for our superinterface
   * (`implements Function<@PolyNull A, @PolyNull B>`), at least as far as I know.)

   * and values are the result of applying the provided mapping functions to the input elements.
   * Entries appear in the result {@code ImmutableBiMap} in encounter order.
   *
   * <p>If the mapped keys or values contain duplicates (according to {@link
   * Object#equals(Object)}), an {@code IllegalArgumentException} is thrown when the collection

   * ImmutableSortedSet}, ordered by the specified comparator.
   *
   * <p>If the elements contain duplicates (according to the comparator), only the first duplicate
   * in encounter order will appear in the result.
   *
   * @since 21.0
   */
  public static <E> Collector<E, ?, ImmutableSortedSet<E>> toImmutableSortedSet(
      Comparator<? super E> comparator) {

 *       returned)
 * </ol>
 *
 * <p>Alas, {@link #reverse} is a little different. As you read backwards through a chain and
 * encounter a call to {@code reverse}, continue working backwards until a result is determined, and
 * then reverse that result.
 *
 * <h3>Additional notes</h3>
 *

 *       returned)
 * </ol>
 *
 * <p>Alas, {@link #reverse} is a little different. As you read backwards through a chain and
 * encounter a call to {@code reverse}, continue working backwards until a result is determined, and
 * then reverse that result.
 *
 * <h3>Additional notes</h3>
 *

public abstract class ImmutableList<E> extends ImmutableCollection<E>
    implements List<E>, RandomAccess {

  /**
   * Returns a {@code Collector} that accumulates the input elements into a new {@code
   * ImmutableList}, in encounter order.
   *
   * @since 21.0
   */
  public static <E> Collector<E, ?, ImmutableList<E>> toImmutableList() {
    return CollectCollectors.toImmutableList();
  }

  /**