+---------+    +---------+
                      |         v    v         |
+---+     +---+     +---+     +--------+     +---+
| G | <-- |   | --> |   | --> |   C    | --> | D |
+---+     | A |     | B |     +--------+     +---+
          |   |     |   |       ^
          |   | --> |   | ------+
          +---+     +---+
            |
            |
            v
          +---+
          | F |
          +---+