%% Author:
%% Date: 5.3.2009

female(amy).
female(johnette).

male(anthony).
male(bruce).
male(ogden).
male(john).

parentof(john,amy).
parentof(amy,johnette).
parentof(amy,anthony).
parentof(amy,bruce).
parentof(ogden,johnette).
parentof(ogden,anthony).
parentof(ogden,bruce).

siblingof(X,Y) :- parentof(Z,X), parentof(Z,Y), X\=Y.

grandfatherof(X,Y) :- parentof(X,Z), parentof(Z,Y), male(X).

granddaughterof(X,Y) :- parentof(Y,Z), parentof(Z,X), female(X).

uncle(X,Y) :- male(X), parentof(Z,Y), siblingof(X,Z).