+--------+ +-----------+
| Bonn | --> | Frankfurt |
+--------+ +-----------+
| ^
| |
v |
+--------+ +-----------+
| Berlin | <-- | Ulm |
+--------+ +-----------+
+--------+ +-----------+
| Bonn | --> | Frankfurt |
+--------+ +-----------+
| ^
| |
v |
+--------+ +-----------+
| Berlin | <-- | Ulm |
+--------+ +-----------+