And default rules the last two action rules

http://www.cs.nps.navy.mil/people/faculty/rowe/book/chap4.html

green arrows, as signals for vehicle traffic. This is what the colors of traffic lights mean: A red light or arrow means "STOP" until the green appears. A flashing RED traffic light or arrow means exactly the same as a stop sign, namely STOP! But after stopping, proceed when safe, observing the right-of-way rules.

[F] If the green arrow is replaced by a flashing red light or arrow, stop for either signal; then go ahead when it's safe to do so.

[G] NEW SIGNALS--Note: California is adopting international symbols to guide pedestrians at street crossings. An upraised hand (orange) means the same as the "WAIT" or "DON'T WALK" sign. A walking person symbol (white) means the same as the "WALK" sign.

http://www.cs.nps.navy.mil/people/faculty/rowe/book/chap4.html

about cars, rules about pedestrians, and default rules (the last two action rules). As we said, defaults are weak prescriptions for general cases, only used if more specific advice cannot be found; for instance, the first default rule says that if nothing prevents you from going forward, go forward.

/* D */ action(car,yield_and_leftturn) :- light(green_arrow,left). /* D */ action(car,yield_and_rightturn) :- light(green_arrow,right).

/* ------ Rules for regular lights ------ */ /* A */ action(car,stop) :- light(red,steady).

/* C */ action(car,slow) :- light(yellow,flashing).

/* A */ action(car,stop) :- light(red_arrow,Direction).

/* H */ action(pedestrian,yield_and_go) :- pedgo(steady).

/* ------ Default rules ------ */
/* I */ action(pedestrian,A) :- not(pedsignals), not(greenfacing), action(car,A).