digraph {
	graph [nodesep=.66,ranksep=.5,splines=line,bgcolor="transparent"]
	edge [penwidth=.75,arrowsize=.75]
	node [shape=circle,style=filled,fillcolor="#cccccc",fontname="Source Code Pro,Ubuntu Mono",penwidth=1.5,width=0.5,margin=0,fontsize=18,label="S"]

	subgraph {rank=same
		A,B,C [style="invis"]
		a,k
	}
	C -> {A B} [style="invis"]
	B -> a [style="invis"]
	a -> {b c d}
	b -> {e f g}
	d -> j
	e -> h
	g -> i

	k -> {l m n}
	l -> o
	n -> {p q r}
	p -> s
	r -> t

	c,q [label="*"]
	f,m [label="+"]
	h,o [label="x"]
	i,s [label="y"]
	j,t [label="z"]
	c,f,h,i,j,m,o,q,s,t [fillcolor="#ffffff"]
}