fruit(orange).

veggie(peas).

junk(chips).

protein(steak).

fiber(cereal).

cal(orange,50). /* a better way: cal(Food,50) :- fruit(Food). */

cal(peas,20).

cal(chips,100).

cal(cereal,100).

cal(steak,200).

/* warning: the following do not work in queries where L is a variable */

good_breakfast(L) :- member(X,L), fiber(X), member(Y,L), fruit(Y).

total([], 0).

total([Head | Tail], T) :- cal(Head,X1), 

			   total(Tail, X2), 

			   T is X1 + X2.

stay_on_diet(L) :- total(L,T), T < 500.

good_diet(L) :- good_breakfast(L), protein(P), member(P,L), stay_on_diet(L).