+ * * * * * * * * * * * * * * * * * * * * +

        *         [8]                [9]          *
                   |                  |
        *          |                  |           *
[1]----[3]--------[5]----------------[6]---------[4]---[2]
        *          |                  |           *
                   |                  |
        *          |                  |           *
                   +--------[7]-------+
        *                                         *

        + * * * * * * *  SR domain  * * * * * * * +