static <A> double sortedPercentage(Cl<A> l, Comparator<A> comparator default null) {
  new Scorer scorer;
  Iterator<A> it = iterator(l);
  if (it.hasNext()) {
    A a = it.next();
    while (it.hasNext()) {
      A b = it.next(); 
      scorer.add(compareWithComparator(comparator, a, b) <= 0);
      a = b;
    }
  }
  ret scorer.percentScore();
}