digraph G {
  graph [rankdir="LR"];
  0 [color="green" shape="doublecircle" style="filled"];
  1 [color="red" shape="circle" style="filled"];
  2 [color="black" shape="circle" style="filled" fillcolor="white"];
  3 [color="red" shape="circle" style="filled"];
  4 [color="black" shape="doublecircle" style="filled"  fillcolor="white"];
  5 [color="black" shape="circle" style="filled"  fillcolor="white"];
  6 [color="black" shape="doublecircle" style="filled" fillcolor="white"];
  7 [color="black" shape="circle" style="filled" fillcolor="white"];
  8 [color="red" shape="circle" style="filled"];
  9 [color="black" shape="doublecircle" style="filled" fillcolor="white"];
  0 -> 1 [label="a"];
  1 -> 3 [label="a"];
  1 -> 4 [label="b"];
  0 -> 2 [label="b"];
  2 -> 5 [label="a"];
  5 -> 7 [label="b"];
  7 -> 8 [label="a"];
  7 -> 9 [label="b"];
  2 -> 6 [label="b"];
}