// Finds out the index of a sublist in the original list
// Works with nested (grand-parent) sublists.
// Does not work with lists not made with subList() (returns -1)

static <A> int magicIndexOfSubList(L<A> list, L<A> sublist) {
  if (sublist == list) ret 0;
  
  ifdef OurSubLists
    if (sublist cast ISubList) {
      L<A> root = sublist.rootList();
      int o2 = sublist.subListOffset();
      if (list cast ISubList) {
        if (list.rootList() != root) ret -1;
        L<A> o1 = list.subListOffset();
        ret o2-o1;
      } else {
        if (list != root) ret -1;
        ret o2;
      }
    }
    ret -1;
  endifdef
  
  ifndef OurSubLists
    Int o2 = cast get(sublist, "offset");
    if (o2 == null) ret -1;
    Int o1 = cast getOpt(list, "offset");
    ret o2-(o1 != null ? o1 : 0);
  endifndef
}