Daniel@0: digraph G {
Daniel@0: 	subgraph cluster_c0 {a0 -> a1 -> a2 -> a3;}
Daniel@0: 	subgraph cluster_c1 {b0 -> b1 -> b2 -> b3;}
Daniel@0: 	x -> a0;
Daniel@0: 	x -> b0;
Daniel@0: 	a1 -> b3;
Daniel@0: 	b3 -> a1;
Daniel@0: }