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

