static <A> L<IntRange> magicSubListsToIntRanges(L<A> original, LL<A> lists) {
  L<IntRange> out = emptyList(lists);
  for (L l : lists) {
    int i = magicIndexOfSubList(original, l);
    if (i < 0) null;
    out.add(intRange(i, i+l(l)));
  }
  ret out;
}