+---------+----+
  |         v    |
+---+     +---+  |
| A |     | C |  |
+---+     +---+  |
  |         ^    |
  |         |    |
  +---------+    |
            |    |
            |    |
            |    |
            v    |
          +---+  |
          | B | <+
          +---+