+------------------------+
| |
| |
+---------+ +----+-------------------+ |
| v | | | |
+---+ +---+ | +---+ +---+----+ |
| U | | I | <+ | A | -------> | B | I | <+
+---+ +---+ +---+ +---+----+
| | |----+
| | C | D |
v +---+----+
+---+ | |
| Z | | E |
+---+ +---+