digraph {
	rankdir="LR";
	subgraph cluster0 {
		graph[rankdir="TB",style="invis"];
		node[shape="plaintext"];
		start[label="promises"];
		forkop[label="\"stdio proc unix sendfd\""];
		acceptop[label="\"stdio unix sendfd\""];
		recvop[label="\"stdio sendfd\""];
		readop[label="\"stdio\""];
	}
	subgraph cluster1 {
		graph[rankdir="TB"];
		start2[label="operations", shape="plaintext"];
		forkop2[label="fork(2)"];
		acceptop2[label="accept(2)"];
		recvop2[label="recvmsg(2)"];
		readop2[label="read(2)"];
	}
	start -> start2[style="invis"];
	forkop -> forkop2[style="invis"];
}