.
                                  b
                         o     o   x     o
                     x         b   o         x
                   b             x              b
                  o              b                o
                 x               o                 x
                 b               x                  b
                o             b     o               o
                x            x        b             x
                 b            o      x             b
                    o           b   o           o
                         x        x         x
                                    b
                                   o
                                    x