return standardLower(e);
    }

    @Override
    public @Nullable T floor(T e) {
      return standardFloor(e);
    }

    @Override
    public @Nullable T ceiling(T e) {
      return standardCeiling(e);
    }

    @Override
    public @Nullable T higher(T e) {
      return standardHigher(e);
    }

    @Override
    public @Nullable T pollFirst() {
      return standardPollFirst();

   * #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may wish to
   * override {@link #ceiling} to forward to this implementation.
   */
  protected @Nullable E standardCeiling(@ParametricNullness E e) {
    return Iterators.getNext(tailSet(e, true).iterator(), null);
  }

  @Override
  public @Nullable E higher(@ParametricNullness E e) {
    return delegate().higher(e);
  }