digraph g {
__start0 [label="" shape="none"]
q0 [shape="doublecircle" label="q0"]
q1 [shape="circle" label="q1"] 
q2 [shape="circle" label="q2"]
q3 [shape="circle" label="q3"]
__start0 -> q0
q0 -> q2[label="a"]
q0 -> q1[label="b"]
q1 -> q3[label="a"]
q1 -> q0[label="b"] 
q2 -> q0[label="a"]
q2 -> q3[label="b"]
q3 -> q1[label="a"]
q3 -> q2[label="b"]

}