}

    @Override
    public @Nullable T lower(T e) {
      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);

   * {@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may
   * wish to override {@link #floor} to forward to this implementation.
   */
  @CheckForNull
  protected E standardFloor(@ParametricNullness E e) {
    return Iterators.getNext(headSet(e, true).descendingIterator(), null);
  }

  @Override
  @CheckForNull
  public E ceiling(@ParametricNullness E e) {
    return delegate().ceiling(e);