digraph test { 
n0[ color=green , fontcolor=red ];
n1;
n2;
n3[ fontcolor=red ];
n0 -> n1[ label= "b"];
n0 -> n1[ label= "c"];
n0 -> n1[ label= "a"];
n1 -> n2[ label= "a"];
n2 -> n3[ label= "b"];
n2 -> n3[ label= "c"];
n2 -> n3[ label= "a"];
n3 -> n1[ label= "b"];
n3 -> n1[ label= "c"];
n3 -> n1[ label= "a"];
}
