% DiscountsR'Us Case study
% See http://www.csci.csusb.edu/dick/cs656/discounts.html
% rules
discount(Day, Person, 10) :- card(Person), tuesday(Day).
discount(D,P,5) :- card(P), not(tuesday(D)).
discount(D,P,10):-senior(P), card(P).
discount(D,P,5):-senior(P), not(card(P)).
discount(D,P,0):-not(senior(P)), not(card(P)).

% facts
tuesday(jan29).
tuesday(jan22).
tuesday(feb5).

card(tricia).
card(maria).

senior(tricia).

person(dick).
person(tricia).
person(maria).

% test: discount(jan29, tricia, X).
% test: discount(jan21, tricia, X).
% test: discount(When, Who, 7).