.
                                     B
                             u    u  l     u
                          l         l  B         l
                        l            u              l
                      B             l                B
                     u              B                u
                     l             u   l                l
                     l              l    l               l
                      B            B u              B
                        u           l l              u
                           l          B            l
                              l       u         l
                                       l
                                       l