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

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

