Test_15d  cost of flow (Kristofides, 342)
1 -   (1 = )
0 -  (1 = )
1 -  (1 = )
4 -  
A B C D
A -> B=1 C=3
B -> C=1 D=3
C -> D=1
D -> 

FLOW:
AB= 0 1
AC= 0 2
BC= 0 1
BD= 0 2
CD= 0 1
