static L<Bits> splitBitsAtElement(L<Bits> l, Bits splitter) {
  l = unnull(l);
  new L<Bits> parts;
  int i = 0;
  while true {
    int j = indexOf(l, splitter, i);
    if (j < 0) {
      parts.add(joinBits(subList(l, i)));
      break;
    }
    parts.add(joinBits(subList(l, i, j)));
    i = j+1;
    while (i < l(l) && eq(l.get(i), splitter)) ++i;
  }
  ret parts;
}