/*  File: family.P
/*  Author: Ned Okie 
/*  Date:   8/24/2007
/*  Purpose: To illustrate backtracking
*/

parent(jack, jill).
parent(jack, joe).
parent(joe, janet).

male(jack).
male(joe).

father(TheDad, TheChild) :- parent(TheDad, TheChild),
                            male(TheDad). 

grandfather(TheGF, TheGC) :- father(TheGF, AParent), parent(AParent, TheGC ).