/* ====================================================== */
/*  Domain Theory and Training Example from Pople's Paper */
/* ====================================================== */
assumable(likes(_,_),likes(_,_)).

distressed(P) :- wants(P,E), believes(P,not(E)).
wants(P,happy(Q)) :- likes(P,Q).
wants(P,E) :- wants(P,S), causes(E,S).

/* Facts */
believes(john,not(pass(mary,exam))).
causes(pass(mary,exam),happy(mary)).

/* Starting Query. */
query :-
  explain_and_learn((distressed(john)),
                    (distressed(X))).