TOPOSORT 7 8 6 9 3 
VARS 2 
1 2 1
2 4 3
NODE 7 0
---1-  1
NODE 7 1
----1  1
NODE 8 0
-1--1  1
NODE 8 1
--01-  1
--1--  1
NODE 6 0
-1---  1
NODE 6 1
--1--  1
NODE 9 0
--11-  1
NODE 9 1
-0--1  1
-1---  1
NODE 3 0
-0011  1
-01-1  1
-101-  1
-11--  1
NODE 3 1
-011-  1
-10-1  1
-1101  1
-111-  1