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

Graph Edges:
1. X12 <-> X10
2. X4 o-> X12
3. X12 <-> X6
4. X10 o-> X6
5. X10 <-> X13
6. X8 o-> X2
7. X4 o-o X7
8. X2 <-> X6
9. X2 <-> X13
10. X6 <-> X1
11. X5 o-> X1
