%% s_course_catalog_1.sp -- SPARC version of course catalog example from
%%    Chapter 5, Section 5.2
%% Last Modified: 2/12/14
%% Knowledge bases with null value 'staff'

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sorts

#prof = {mike, john}.
#prof_values = #prof + {staff}.
#course = {pascal, c, prolog}.
#default = d(#prof_values, #course).

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predicates

teaches(#prof_values, #course).
ab(#default).

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rules

teaches(mike,pascal).
teaches(john,c).
teaches(staff,prolog).

-teaches(P,C) :- not ab(d(P,C)), 
                 not teaches(P,C).
                 
ab(d(P,C)) :- teaches(staff,C).