static L<IntRange> invertIntRanges(L<IntRange> l, int start, int end) {
  new L<IntRange> out;
  int x = start, i = 0;
  while (i < l(l)) {
    int y = l.get(i).start;
    if (y > x) out.add(intRange(x, y));
    x = l.get(i).end;
    ++i;
  }
  if (end > x) out.add(intRange(x, end));
  ret out;
}