digraph g { node [shape=circle]; 0 -> 1 [label=A] 0 -> 3 [label=B] 0 -> 3 [label=C] 1 -> 3 [label=A] 1 -> 2 [label=B] 1 -> 3 [label=C] 2 -> 2 [label=A] 2 -> 2 [label=B] 2 -> 2 [label=C] 3 -> 3 [label=A] 3 -> 3 [label=B] 3 -> 3 [label=C] }