private static Move BackwardLeftForWhite(int r, int c, Board board){
        Move backwardLeft = null;
        if( r>=1 && c>=1 &&
                board.cell[r-1][c-1] == CellEntry.empty
          )
        {
            backwardLeft = new Move(r,c, r-1, c-1);
        }
        return backwardLeft;
    }