public void testHash() {
   final HashSet<Phrase> hs = new HashSet<Phrase>();
   hs.add(new Phrase(new int[] {1, 2}));
   assertTrue(hs.contains(new Phrase(new int[] {0, 1, 2, 3}, 1, 2)));
   hs.clear();
   hs.add(new Phrase(new int[] {0, 1, 2, 3}, 1, 2));
   assertTrue(hs.contains(new Phrase(new int[] {1, 2})));
 }