digraph G {
	subgraph cluster_0 {
		a0 -> a1 -> a2 -> a3;
	}

	subgraph cluster_1 {
		b0 -> b1 -> b2 -> b3;
	}
	start -> a0;
	start -> b0;
	a1 -> b3;
	b2 -> a3;
	a3 -> a0;
	a3 -> end;
	b3 -> end;
}
