code: @Override
    protected SortedSet<E> standardSubSet(E fromElement, E toElement) {
      return subSet(fromElement, true, toElement, false);
    }
docs: A sensible definition of {@link #subSet(Object, Object)} in terms of the {@link #subSet(Object,
  boolean, Object, boolean)} method. If you override {@link #subSet(Object, boolean, Object,
  boolean)}, you may wish to override {@link #subSet(Object, Object)} to forward to this
  implementation.