graph ex3pt1 { node [texmode="math",shape="none"]; S0 [label="S"]; S1 [label="S"]; a0 [label="a"]; S2 [label="S"]; S3 [label="S"]; a1 [label="a"]; S4 [label="S"]; b0 [label="b"]; b1 [label="b"]; b2 [label="b"]; S0 -- S1; S0 -- a0; S0 -- S2; S1 -- S3; S1 -- a1; S1 -- S4; S2 -- b0; S3 -- b1; S4 -- b2; }