.

                                      T
                      ­       r     r   u     r
                         u         e   T       u
                       T             r              T
                     r               u                 r
                   u                e                  u
                   e                 T                   e
                   T             r       u              T
                    r             e       T              r
                     u            r     u              u
                       e              e                 e
                         T            T              T
                            r      ­    r            r
                              u       u         u
                                   e   e    e
                                        T
                ­                        r
                                       ­ u
                                        e