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

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

