protected E standardLower(E e) {
    return Iterators.getNext(headSet(e, false).descendingIterator(), null);
  }
protected E standardLower ( E e ) { return Iterators . getNext ( headSet ( e , false ) . descendingIterator ( ) , null ) ; }
A sensible definition of {@link #lower} in terms of the {@code descendingIterator} method of
{@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may
wish to override {@link #lower} to forward to this implementation.