t

                                                                     t   S
                                                                 t   S
                                                             t   S
                                                         t   S
                                                     t   S
                                                 t   S
                                             t   S                       *
                                         t   S                   *   *
                                     t   S               *   *
                             t   S   S           *   *
 t   t   t   t   t   t   S   S           *   *
 S   S   S   S   S   S           *   *
                         *   *
                 *   *           S   S   S   S   S   S   S   S   S   S   S
         *   *           S   S   t   t   t   t   t   t   t   t   t   t   t
 *   *               S   t
                 S   t
             S   t
         S   t
     S   t
 S   t
 t