int skipped = advance(iterator, position);
    if (!iterator.hasNext()) {
      throw new IndexOutOfBoundsException(
          "position ("
              + position
              + ") must be less than the number of elements that remained ("
              + skipped
              + ")");
    }
    return iterator.next();
  }

  /**

   * any of the public methods of ListenableFuture.
   */
  interface Trusted<V extends @Nullable Object> extends ListenableFuture<V> {}

  /**
   * A less abstract subclass of AbstractFuture. This can be used to optimize setFuture by ensuring
   * that {@link #get} calls exactly the implementation of {@link AbstractFuture#get}.
   */

  @GwtCompatible(serializable = true)
  public <S extends T> Ordering<S> reverse() {
    return new ReverseOrdering<>(this);
  }

  /**
   * Returns an ordering that treats {@code null} as less than all other values and uses {@code
   * this} to compare non-null values.
   *
   * <p>The returned object is serializable if this object is serializable.
   *

  @GwtIncompatible // NavigableMap
  private static class FilteredEntryNavigableMap<
          K extends @Nullable Object, V extends @Nullable Object>
      extends AbstractNavigableMap<K, V> {
    /*
     * It's less code to extend AbstractNavigableMap and forward the filtering logic to
     * FilteredEntryMap than to extend FilteredEntrySortedMap and reimplement all the NavigableMap
     * methods.
     */