.
                                      B
                              u     u g     u
                            g       B u        g
                           B         g            B
                          u        B   u          u
                          g       g      B         g
                          B       u      g         B
                           u        B   u         u
                              g         g         g
                                 B      B      B
                                      u    u
                                         g