Graph Nodes:
X1;X2;X3;X4;X5;X6;X7;X8;X9;X10;X11;X12;X13

Graph Edges:
1. X1 --> X2
2. X1 --> X3
3. X1 --> X6
4. X1 --> X9
5. X10 --> X13
6. X2 --> X12
7. X3 --> X7
8. X4 --> X10
9. X4 --> X11
10. X4 --> X13
11. X4 --> X6
12. X5 --> X11
13. X5 --> X9
14. X6 --> X10
15. X7 --> X11
16. X7 --> X12
17. X7 --> X8
18. X8 --> X11
19. X8 --> X12
20. X9 --> X12

