digraph G {
size="6,6";
	a -> b -> c;

	subgraph cluster0 {
		x0 -> y0;
		x0 -> z0;
	}

	subgraph cluster1 {
		x1 -> y1;
		x1 -> z1;
	}

	subgraph cluster2 {
		x2 -> y2;
		x2 -> z2;
	}

	a -> x0;
	b -> x1;
	b -> x2;
	a -> z2;
	c -> z1;
}