*/
  @Override
  public SortedMap<C, V> row(R rowKey) {
    return new TreeRow(rowKey);
  }

  private class TreeRow extends Row implements SortedMap<C, V> {
    @CheckForNull final C lowerBound;
    @CheckForNull final C upperBound;

    TreeRow(R rowKey) {
      this(rowKey, null, null);
    }

    TreeRow(R rowKey, @CheckForNull C lowerBound, @CheckForNull C upperBound) {
      super(rowKey);