}

  public void testHeadSet_E() {
    NavigableSet<String> set = create();
    SortedSet<String> headSet = set.headSet("a");
    assertTrue(headSet instanceof SynchronizedSortedSet);
    assertSame(set, ((SynchronizedSortedSet<String>) headSet).mutex);
  }

  public void testHeadSet_E_B() {
    NavigableSet<String> set = create();

  }

  public void testHeadSet_E() {
    NavigableSet<String> map = create();
    SortedSet<String> headSet = map.headSet("a");
    assertTrue(headSet instanceof SynchronizedSortedSet);
    assertSame(MUTEX, ((SynchronizedSortedSet<String>) headSet).mutex);
  }

  public void testHeadSet_E_B() {
    NavigableSet<String> map = create();