var mm_move = function (fx, fy, tx, ty, promotion)

        {
        this . fx = fx - 0;
        this . fy = fy - 0;
        this . tx = tx - 0;
        this . ty = ty - 0;
        this . promotion = promotion;

        this . piece = null;            // not stored on the server
        this . captured_piece = null;   // not stored on the server
        };