digraph G {
subgraph cluster_c0 {a0 -> a1 -> a2 -> a3;}
subgraph cluster_c1 {b0 -> b1 -> b2 -> b3;}
x -> a0;
x -> b0;
a1 -> a3;
a3 -> a0;
}
digraph G {
subgraph cluster_c0 {a0 -> a1 -> a2 -> a3;}
subgraph cluster_c1 {b0 -> b1 -> b2 -> b3;}
x -> a0;
x -> b0;
a1 -> a3;
a3 -> a0;
}