/* simpsons.pl */

parent(P,C) :- child(C,P).		 % parent is the inverse of child
husband(H,W) :- spouse(H,W), male(H).    % a husband is a male spouse
mother(M,C) :- parent(M,C), female(M).	 % a mother is a female parent

/* some facts about the Simspons */
male(homer).
spouse(homer,marge).
child(bart, homer).
child(maggie,homer).
child(lisa, homer).
child(lisa, marge).
female(marge).