public interface SortedSet<E> extends Set<E> {
    // Range-view
    SortedSet<E> subSet(E fromElement, E toElement);
    SortedSet<E> headSet(E toElement);
    SortedSet<E> tailSet(E fromElement);
    
    // Endpoints
    E first();
    E last();

    // Comparator access
    Comparator<? super E> comparator();
}