public void playPrev(ref GoMove gm)

        {

            Point p = gm.Point;

            m_colorToPlay = gm.Color;

            clearLabelsAndMarksOnBoard();

            m_gmLastMove = gameTree.peekPrev();

            bDrawMark = true;

            Grid[p.X, p.Y].die();

            if (gm.DeadGroup != null)

            {

                foreach (Point s in gm.DeadGroup)

                {

                    Grid[s.X, s.Y].setStone(gm.DeadGroupColor);

                }

            }

            optRepaint();

            textBox1.Clear();

            textBox1.AppendText(gm.Comment);

            return;

        }