@Override
   public boolean removeAll(IntSet set) {
      throw new UnsupportedOperationException("RangeSet is immutable");
   }
@Test(expected = UnsupportedOperationException.class)
   public void removeAll() throws Exception {
      RangeSet rs = new RangeSet(4);

      RangeSet rs2 = new RangeSet(6);

      rs.removeAll(rs2);
   }