/* Term ordering example. */
/* This example demonstrates how different orders in the
   body of the father predicate can make a
   big difference in efficency. */
/* Note, a predicate of the form pred(X,Y) should be read "X is the pred of Y" */

parent(P,C) :- child(C,P).
father(F,C) :- male(F), child(C,F).               % inefficient
father2(F,C) :- child(C,F), male(F).              % efficient
mother(M,C) :- child(C,M), female(M).

female(marge).
female(maggie).
female(lisa).
male(mr_burns).
male(krusty).
male(wiggum).
male(ralph).
male(homer).
male(bart).
child(lisa, marge).
child(lisa, homer).
child(bart, homer).
child(maggie, homer).