% A third family relationships program}
% progpar3.pl

parent(henry_II, john).
parent(john, henry_III).
parent(isabella, henry_III).
parent(henry_III, edward_I).

grandparent(henry_II, henry_III).
grandparent(john, edward_I).
grandparent(isabella, edward_I).

greatgrandparent(henry_II, edward_I).