public R lastKey() {
      return sortedBackingMap().lastKey();
    }

    @Override
    public SortedMap<R, Map<C, V>> headMap(R toKey) {
      checkNotNull(toKey);
      return new StandardRowSortedTable<R, C, V>(sortedBackingMap().headMap(toKey), factory)
          .rowMap();
    }

    @Override
    public SortedMap<R, Map<C, V>> subMap(R fromKey, R toKey) {
      checkNotNull(fromKey);

    public R lastKey() {
      return sortedBackingMap().lastKey();
    }

    @Override
    public SortedMap<R, Map<C, V>> headMap(R toKey) {
      checkNotNull(toKey);
      return new StandardRowSortedTable<R, C, V>(sortedBackingMap().headMap(toKey), factory)
          .rowMap();
    }

    @Override
    public SortedMap<R, Map<C, V>> subMap(R fromKey, R toKey) {
      checkNotNull(fromKey);

  @Override
  public boolean containsRow(@Nullable Object rowKey) {
    return Maps.safeContainsKey(rowMap(), rowKey);
  }

  @Override
  public boolean containsColumn(@Nullable Object columnKey) {
    return Maps.safeContainsKey(columnMap(), columnKey);
  }

  @Override
  public Set<R> rowKeySet() {
    return rowMap().keySet();
  }

  @Override
  public Set<C> columnKeySet() {
    return columnMap().keySet();

    return delegate.get(checkValid(key));
  }

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

  @Override
  public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
    return new SafeTreeMap<>(delegate.headMap(checkValid(toKey), inclusive));
  }

  @Override
  public @Nullable Entry<K, V> higherEntry(K key) {

  @Override
  public boolean containsRow(@Nullable Object rowKey) {
    return Maps.safeContainsKey(rowMap(), rowKey);
  }

  @Override
  public boolean containsColumn(@Nullable Object columnKey) {
    return Maps.safeContainsKey(columnMap(), columnKey);
  }

  @Override
  public Set<R> rowKeySet() {
    return rowMap().keySet();
  }

  @Override
  public Set<C> columnKeySet() {
    return columnMap().keySet();

      return entry.getKey();
    }
  }

  @Override
  public @Nullable Entry<K, V> lowerEntry(@ParametricNullness K key) {
    return headMap(key, false).lastEntry();
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(@ParametricNullness K key) {
    return headMap(key, true).lastEntry();
  }

  @Override
  public @Nullable Entry<K, V> ceilingEntry(@ParametricNullness K key) {

      return entry.getKey();
    }
  }

  @Override
  public @Nullable Entry<K, V> lowerEntry(@ParametricNullness K key) {
    return headMap(key, false).lastEntry();
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(@ParametricNullness K key) {
    return headMap(key, true).lastEntry();
  }

  @Override
  public @Nullable Entry<K, V> ceilingEntry(@ParametricNullness K key) {

  @Override
  public ImmutableMap<R, Map<C, V>> rowMap() {
    // Casts without copying.
    return ImmutableMap.copyOf(rowMap);
  }

  @Override
  public int size() {
    return cellRowIndices.length;
  }

  @Override
  Cell<R, C, V> getCell(int index) {
    int rowIndex = cellRowIndices[index];
    Entry<R, ImmutableMap<C, V>> rowEntry = rowMap.entrySet().asList().get(rowIndex);

  }

  @Override
  @ParametricNullness
  public K firstKey() {
    return delegate().firstKey();
  }

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

  @Override
  @ParametricNullness
  public K lastKey() {
    return delegate().lastKey();
  }

  @Override

  @Override
  public ImmutableMap<R, Map<C, V>> rowMap() {
    // Casts without copying.
    return ImmutableMap.copyOf(rowMap);
  }

  @Override
  public int size() {
    return cellRowIndices.length;
  }

  @Override
  Cell<R, C, V> getCell(int index) {
    int rowIndex = cellRowIndices[index];
    Entry<R, ImmutableMap<C, V>> rowEntry = rowMap.entrySet().asList().get(rowIndex);