static <A> Comparator<L<A>> listComparator() {
  ret (a, b) -> {
    int l1 = l(a), l2 = l(b);
    for (int i = 0; ; i++) {
      if (i >= l1) ret i >= l2 ? 0 : -1;
      if (i >= l2) ret 1;
      int c = cmp(a.get(i), b.get(i));
      if (c != 0) ret c;
    }
  };
}

static <A> Comparator<L<A>> listComparator(Comparator<A> comparator) {
  if (comparator == null) ret listComparator();
  
  ret (a, b) -> {
    int l1 = l(a), l2 = l(b);
    for (int i = 0; ; i++) {
      if (i >= l1) ret i >= l2 ? 0 : -1;
      if (i >= l2) ret 1;
      int c = comparator.compare(a.get(i), b.get(i));
      if (c != 0) ret c;
    }
  };
}