true.

?- good_to_eat(What).
What = apple.

?- good_to_eat(apple).
true.

?- good_to_eat(chocolate).
false.

?- healthy(peanut_butter).
false.

?- healthy(Which); food(Which).
Which = running ;;
Which = apple ;;
Which = potato_chips ;;
Which = apple.

?- food(Which); healthy(Which).
Which = potato_chips ;;
Which = apple ;;
Which = running ;;
Which = apple.

?- halt.