             *   . .   . #          |
|      . .  .     .  . .         *   . .  .     .  # .      |
|     ..   .       .   ...   *      ..   .       .   #.#    |
|    o    o         o    o         o    o         o    o    |
|    m    h         k    w       &quot;m&quot;   &quot;h&quot;       &quot;k&quot;   &quot;w&quot;  |
|   S_1  S_2       S_3  S_4     &quot;S_1&quot; &quot;S_2&quot;     &quot;S_3&quot; &quot;S_4&quot; |
|                                                           |
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