+-------------------------+
                             |                         |
                      +------+                         +---------------+
           +----------+                                                |
           |                                                           +----------+
           |                                                                      |
           |                    XXX                                               --------+
           |                    XXX                                                       |
+----------+                                                              XXX             +-------+
|                                                                         XXX                     |
|                                            UUU                                                  |
|                                            UUU                                                  |
|                                                                                                 +----------+
+------                                                                                                      |
      |                                                      XXX                                             |
      |                                                      XXX                                             |
      |                                                                                                      |
      |                                                                                                      |
      ++                                                                                                     |
       |                           XXX                                                                       |
       |                           XXX                                                                       |
       +--------+                                               XXX                                          |
                |                                               XXX                                          |
                |                                                                                            |
                |                                                                           +----------------+
            +---+                                                                           |
            |                                                                               |
            |                                                         +---------------------+
            |                                                         |
            |                                           +------------+
            |            |------------------------------+
            +------------+