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