%Prolog Example - Geneology 
%Author - Dan Schlegel
%Modified - 11/7/2010

son(S, P) :- man(S), parent(P, S).
daughter(D, P) :- woman(D), parent(P, D).

childOf(C, P) :- parent(P, C).

childOf(C, P1, P2) :- parent(P1, C), parent(P2, C), P1\=P2.

sibling(S1, S2) :- parent(Parent, S1), parent(Parent, S2), S1\=S2.

aunt(A, P) :- parent(Parent, P), sibling(Parent, A), woman(A).

uncle(U, P) :- parent(Parent, P), sibling(Parent, U), man(U).

grandparent(GP, P) :- parent(Parent, P), parent(GP, Parent).

%You'll note that ancestor is the transitive closure of 'Parent'.
ancestor(A, P) :- ancestor(A, P, _). %Bad form in Prolog, you shouldn't do this!
ancestor(A, P, L) :- parent(A, P), L is 1.
ancestor(A, P, L) :- parent(Parent, P), ancestor(A, Parent, M), L is M+1.

descendent(D, P, L) :- ancestor(P, D, L).

commonancestor(A, P1, P2) :- ancestor(A, P1, L1), ancestor(A, P2, L2), L1=L2, P1\=P2.

cousin(C, P) :- grandparent(GP, P), commonancestor(GP, C, P).

man(tom).
man(adam).
man(alex).
woman(betty).
woman(mary).
woman(kate).

parent(tom, mary).
parent(tom, adam).
parent(betty, mary).
parent(betty, adam).
parent(adam, alex).
parent(mary, kate).

%A trap not to fall in to...
%childOf(betty, mary, adam).



%%%Questions.
grandparent(X, kate).
aunt(A, kate).
uncle(U, kate).
descendent(D, tom, _).
cousin(X, Y).

%Lets add some rules... 
%nephew
%great-granddaughter