code: @Override
    public HashIntSet symmetricDifference(IntSet c)
    {
      HashIntSet res = clone();
      IntIterator itr;
      if (c instanceof HashIntSet) {
        itr = ((HashIntSet) c).unsortedIterator();
      } else {
        itr = c.iterator();
      }
      while (itr.hasNext()) {
        res.flip(itr.next());
      }
      return res;
    }
docs: {@inheritDoc}