male(alistair).
male(andrew).
male(benjamin).
male(caleb).
male(david).
male(james).
male(john).
female(alison).
female(ann).
female(beatrice).
female(clara).
female(diana).
female(jane).
female(joan).
parent(beatrice, james).
parent(beatrice, john).
parent(benjamin, james).
parent(benjamin, john).
parent(caleb, benjamin).
parent(clara, benjamin).
parent(james, andrew).
parent(james, ann).
parent(jane, david).
parent(jane, diana).
parent(joan, andrew).
parent(joan, ann).
parent(john, david).
parent(john, diana).
grandparent(Grandp, Child) :-
parent(Grandp, Parent),
parent(Parent, Child).
-
In the following solutions, it doesn't matter in terms of the correctness
of the program if female/1 and male/1 are placed before or after the grandparent/2
goal.
grandmother(Grannie, Child) :-
grandparent(Grannie, Child),
female(Grannie).
grandfather(Grandpa, Child) :-
grandparent(Grandpa, Child),
male(Grandpa).
ancestor(Current, Anc) :- % 1
parent(Anc, Current).
ancestor(Current, Anc) :- % 2
parent(Anc, Via),
ancestor(Current, Via).
