// This graph uses special PGF/TikZ styles to create some interesting
// visual effects. To get the snaked edges run dot2tex with the -s option
// to force straight edges. Example
// $ fdp -Txdot balls.dot | dot2tex -s > balls.tex
graph G {
	node [shape=circle, fixedsize=True, width="0.2", style="ball color = green", label=""];
	edge [style="snake=zigzag, green"];
	a_1 -- c -- a_2;
	c [style="ball color=black"];
	edge [style="snake=snake, blue", color=red];
	node [style="ball color = red", label=""];
	a_3 -- c -- a_4 --a_3;
}