@Override
   public boolean containsAll(IntSet set) {
      return set.isEmpty();
   }
@Test
   public void testContainsAll() throws Exception {
      IntSet sis2 = new SingletonIntSet(3);

      assertFalse(es.containsAll(sis2));
      assertTrue(sis2.containsAll(es));

      IntSet sis3 = new RangeSet(0);

      assertTrue(sis3.containsAll(es));
      assertTrue(es.containsAll(sis3));
   }