.
                                        
                      ­                    L
                                     i   ib   i
                                  b     er     b
                               e        ty         e
                              r          L            r
       ­                       t        i      b        t
               ­               L       e      t         L
                               i        b    e         i
                                b       r   t         b
                                 e         y         e
                                    r      L        r
         ­                             t     i      t
                                         y b  y
                                             e
                                             t
                                             y