/* ======================================================== */
/* Authors: Smadar Kedar-Cabelli & Thorne McCarty (Rutgers) */
/* This is the example from their MLW 1987 paper. */
/* ======================================================== */

/* Goal concept, as Mitchell, Keller & Kedar-Cabelli called it. */
kill(A,B) :- hate(A,B), possess(A,C), weapon(C).

/* Domain Theory. */
hate(W,W) :- depressed(W).
possess(U,V) :- buy(U,V).
weapon(Z) :- gun(Z).

/* Training Example. */
depressed(john).
buy(john,gun1).
gun(gun1).

/* Query.  Invoked using something analogous to "q(P,G)." */
query :- explain_and_store(kill(john,john),kill(X,Y)).