digraph finite_automata {
 /* graph properties */
 graph [rankdir=LR label="hw1.fa"];
 node [style=filled fillcolor="#E0E0E0"];
 /* states */
 1 [shape=doublecircle];
 2 [shape=doublecircle];
 3 [shape=circle];
 invis_start [style=invis];
 /* transitions */
 invis_start -> 1 [label=" "];
 1 -> 1 [label="a"];
 1 -> 3 [label="b"];
 2 -> 1 [label="b"];
 2 -> 3 [label="a"];
 3 -> 2 [label="b"];
 3 -> 3 [label="a"];
}