SortedMap<String, Integer> subMap = map.subMap("a", "b");
    assertTrue(subMap instanceof SynchronizedSortedMap);
    assertSame(mutex, ((SynchronizedSortedMap<String, Integer>) subMap).mutex);
  }

  public void testSubMap_K_B_K_B() {
    NavigableMap<String, Integer> map = create();
    NavigableMap<String, Integer> subMap = map.subMap("a", true, "b", false);
    assertTrue(subMap instanceof SynchronizedNavigableMap);

    return descendingMap().navigableKeySet();
  }

  /**
   * A sensible definition of {@link #subMap(Object, Object)} in terms of {@link #subMap(Object,
   * boolean, Object, boolean)}. If you override {@code subMap(K, boolean, K, boolean)}, you may
   * wish to override {@code subMap} to forward to this implementation.
   */
  @Override
  protected SortedMap<K, V> standardSubMap(

    Entry<K, V> secondEntry = iterator.next();
    K key = secondEntry.getKey();
    SortedMap<K, V> subMap = map.tailMap(key);
    subMap.remove(key);
    assertNull(subMap.remove(firstEntry.getKey()));
    assertEquals(map.size(), oldSize - 1);
    assertFalse(map.containsKey(key));
    assertEquals(subMap.size(), oldSize - 2);
  }

  public void testTailMapClearThrough() {
    SortedMap<K, V> map;
    try {

    Entry<K, V> secondEntry = iterator.next();
    K key = secondEntry.getKey();
    SortedMap<K, V> subMap = map.tailMap(key);
    subMap.remove(key);
    assertNull(subMap.remove(firstEntry.getKey()));
    assertEquals(map.size(), oldSize - 1);
    assertFalse(map.containsKey(key));
    assertEquals(subMap.size(), oldSize - 2);
  }

  public void testTailMapClearThrough() {
    SortedMap<K, V> map;
    try {

  }

  @Override
  public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
    return new SafeTreeMap<>(
        delegate.subMap(checkValid(fromKey), fromInclusive, checkValid(toKey), toInclusive));
  }

  @Override
  public SortedMap<K, V> subMap(K fromKey, K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override

  }

  @Override
  public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
    return new SafeTreeMap<>(
        delegate.subMap(checkValid(fromKey), fromInclusive, checkValid(toKey), toInclusive));
  }

  @Override
  public SortedMap<K, V> subMap(K fromKey, K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override

    assertEquals(ImmutableMap.of("banana", 6, "dog", 3), filtered.headMap("emu"));

    assertEquals(ImmutableMap.of("banana", 6), filtered.subMap("banana", "dog"));
    assertEquals(ImmutableMap.of("dog", 3), filtered.subMap("cat", "emu"));

    assertEquals(ImmutableMap.of("dog", 3), filtered.tailMap("cat"));
    assertEquals(ImmutableMap.of("banana", 6, "dog", 3), filtered.tailMap("banana"));
  }

    TreeBasedTable<String, Integer, Character> table = makeTable();
    populateTable(table);
    return table.rowMap().subMap("b", "x");
  }

  @Override
  protected Map<String, Map<Integer, Character>> makeEmptyMap() {
    return makeTable().rowMap().subMap("b", "x");
  }

  @Override
  protected String getKeyNotInPopulatedMap() {
    return "z";
  }

   * This method returns a {@code ImmutableSortedMap}, consisting of the entries whose keys ranges
   * from {@code fromKey}, inclusive, to {@code toKey}, exclusive.
   *
   * <p>The {@link SortedMap#subMap} documentation states that a submap of a submap throws an {@link
   * IllegalArgumentException} if passed a {@code fromKey} less than an earlier {@code fromKey}.
   * However, this method doesn't throw an exception in that situation, but instead keeps the

    /**
     * Usually the same as map, but smaller for the headMap(), tailMap(), or subMap() of a
     * SortedAsMap.
     */
    final transient Map<K, Collection<V>> submap;

    AsMap(Map<K, Collection<V>> submap) {
      this.submap = submap;
    }

    @Override
    protected Set<Entry<K, Collection<V>>> createEntrySet() {
      return new AsMapEntries();