%% cars.cr -- CR-Prolog solution to additional exercise for Section 5.5 
%% (Indirect Exceptions to Defaults)
%% Last Modified: 3/26/14
%% You can run it with CR-Models:
%%   crmodels cr_cars.cr
%%
%% Write a program with consistency restoring rules
%% representing the following information:
%% "Cars normally work; in rare cases, a car does not work.
%% Working cars have working engines. 
%% The engine of John's car does not work."
%% Make sure that your program entails that John's car does not work but 
%% Mary's car does.

car(c1).
car(c2).

works(C) :-
        car(C),
        not ab(d(C)),
        not -works(C).

#domain car(C).  %% #domain required for cr-rules of CRModels
r1(C): -works(C) +-.

works(e(C)) :-
        car(C),
        works(C).

owns(john,c1).
-works(e(c1)).
owns(mary,c2).