public void testLast() {
    assertEquals(c.getKey(), navigableMap.lastKey());
  }

  @CollectionSize.Require(absent = ZERO)
  public void testHeadMapExclusive() {
    assertFalse(navigableMap.headMap(a.getKey()).containsKey(a.getKey()));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testTailMapInclusive() {
    assertTrue(navigableMap.tailMap(a.getKey()).containsKey(a.getKey()));
  }

   *
   * <p>The {@link SortedMap#headMap} documentation states that a submap of a submap throws an
   * {@link IllegalArgumentException} if passed a {@code toKey} greater than an earlier {@code
   * toKey}. However, this method doesn't throw an exception in that situation, but instead keeps
   * the original {@code toKey}.
   */
  @Override
  public ImmutableSortedMap<K, V> headMap(K toKey) {
    return headMap(toKey, false);
  }

  public void testLast() {
    assertEquals(c.getKey(), navigableMap.lastKey());
  }

  @CollectionSize.Require(absent = ZERO)
  public void testHeadMapExclusive() {
    assertFalse(navigableMap.headMap(a.getKey()).containsKey(a.getKey()));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testTailMapInclusive() {
    assertTrue(navigableMap.tailMap(a.getKey()).containsKey(a.getKey()));
  }

  }

  @CollectionSize.Require(absent = ZERO)
  public void testHeadMapExclusive() {
    assertFalse(navigableMap.headMap(a.getKey(), false).containsKey(a.getKey()));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testHeadMapInclusive() {
    assertTrue(navigableMap.headMap(a.getKey(), true).containsKey(a.getKey()));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testTailMapExclusive() {

      checkArgument(rangeContains(checkNotNull(fromKey)) && rangeContains(checkNotNull(toKey)));
      return new TreeRow(rowKey, fromKey, toKey);
    }

    @Override
    public SortedMap<C, V> headMap(C toKey) {
      checkArgument(rangeContains(checkNotNull(toKey)));
      return new TreeRow(rowKey, lowerBound, toKey);
    }

    @Override
    public SortedMap<C, V> tailMap(C fromKey) {

   *
   * <p>The {@link SortedMap#headMap} documentation states that a submap of a submap throws an
   * {@link IllegalArgumentException} if passed a {@code toKey} greater than an earlier {@code
   * toKey}. However, this method doesn't throw an exception in that situation, but instead keeps
   * the original {@code toKey}.
   */
  @Override
  public ImmutableSortedMap<K, V> headMap(K toKey) {
    return headMap(toKey, false);
  }

      NavigableMap<K, V> map = (NavigableMap<K, V>) sortedMap;
      if (from == Bound.NO_BOUND && to == Bound.INCLUSIVE) {
        return map.headMap(lastInclusive, true);
      } else if (from == Bound.EXCLUSIVE && to == Bound.NO_BOUND) {
        return map.tailMap(firstExclusive, false);
      } else if (from == Bound.EXCLUSIVE && to == Bound.EXCLUSIVE) {

      }
    }

    @Override
    public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
      synchronized (mutex) {
        return navigableMap(delegate().headMap(toKey, inclusive), mutex);
      }
    }

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

    @Override
    @CheckForNull

      }
    }

    @Override
    public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
      synchronized (mutex) {
        return navigableMap(delegate().headMap(toKey, inclusive), mutex);
      }
    }

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

    @Override
    @CheckForNull

      NavigableMap<K, V> map = (NavigableMap<K, V>) sortedMap;
      if (from == Bound.NO_BOUND && to == Bound.INCLUSIVE) {
        return map.headMap(lastInclusive, true);
      } else if (from == Bound.EXCLUSIVE && to == Bound.NO_BOUND) {
        return map.tailMap(firstExclusive, false);
      } else if (from == Bound.EXCLUSIVE && to == Bound.EXCLUSIVE) {