static <A> bool isSortedListByComparator(Cl<A> l, Comparator<A> cmp) {
  Iterator<A> it = iterator(l);
  if (!it.hasNext()) true;
  A a = it.next();
  while (it.hasNext()) {
    A b = it.next(); 
    if (cmp.compare(a, b) > 0)
      false;
    a = b;
  }
  true;
}