static L<IntRange> mergeIntRangesCloserThan(final int threshold, L<IntRange> l) {
  new L<IntRange> out;
  for (IntRange r : l)
    if (nempty(out) && r.start <= last(out).end+threshold)
      replaceLast(out, intRange(last(out).start, r.end));
    else
      out.add(r);
  ret out;
}