private BdynRangeSet pruneRange(BdynRangeSet rslt, long t0, long t1) {
    if (rslt == null) return null;

    for (Iterator<Set<BdynEntry>> it = rslt.values().iterator(); it.hasNext(); ) {
      Set<BdynEntry> vals = it.next();
      int ct = 0;
      for (Iterator<BdynEntry> it1 = vals.iterator(); it1.hasNext(); ) {
        BdynEntry oe = it1.next();
        if (oe.getEndTime(t1) < t0) it1.remove();
        else ++ct;
      }
      if (ct == 0) it.remove();
    }

    if (rslt.size() == 0) return null;

    return rslt;
  }