graph LR
A --> B
C --> D
---
+---+     +---+
|   |     |   |
| A |---->| B |
|   |     |   |
+---+     +---+
               
               
               
               
               
+---+     +---+
|   |     |   |
| C |---->| D |
|   |     |   |
+---+     +---+
