/* Example of NFA simulation, Bratko, Section 4.3, Figure 4.3 */
final( s3).

trans( s1, a, s1).
trans( s1, a, s2).
trans( s1, b, s1).
trans( s2, b, s3).
trans( s3, b, s4).

silent( s2, s4).
silent( s3, s1).

accepts( State, []) :- final( State). % Accepts empty string
accepts( State, [ X | Rest]) :-
  trans( State, X, State1),
  accepts( State1, Rest).
accepts( State, String) :-
  silent( State, State1),
  accepts( State1, String).