% Some simple test Prolog programs
% --------------------------------

% Knowledge bases

male('Haakon VII').
male('Olav V').
male('Harald V').
male('Haakon').
female('Martha').
female('Mette-Marit').
female('Maud').
female('Sonja').
parent('Haakon VII','Olav V').
parent('Maud','Olav V').
parent('Olav V','Harald V').
parent('Martha','Harald V').
parent('Harald V','Haakon').
parent('Sonja','Haakon').

father(X, Y) :-
    parent(X, Y),
    male(X).

mother(X, Y) :-
    parent(X, Y),
    female(X).

sibling(X, Y) :-
    parent(Z, X),
    parent(Z, Y).

brother(X, Y) :-
    sibling(X, Y),
    male(X).

sister(X, Y) :-
    sibling(X, Y),
    female(X).

spouse(X, Y) :-
    parent(X, Z),
    parent(Y, Z).

% X is the brother-in-law of Y
brother_in_law(X, Y) :-
    male(X),
    sibling(X, A),
    spouse(A, Y).

sister_in_law(X, Y) :-
    female(X),
    sibling(X, A),
    spouse(A, Y).

uncle(X, Y) :-
    male(X),
    sibling(X, A),
    parent(A, Y).

aunt(X, Y) :-
    female(X),
    sibling(X, A),
    parent(A, Y).

grandmother(X, Y) :-
    female(X),
    parent(X, A),
    parent(A, Y).

grandfather(X, Y) :-
    male(X),
    parent(X, A),
    parent(A, Y).

cousin(X, Y) :-
    uncle(A, X),
    	aunt(A, X),
    parent(A, Y).

ancestor(X, Y) :-
    parent(X, Y).

ancestor(X, Y) :-
    parent(X, Z),
    ancestor(Z, Y).

descendant(X, Y) :-
    parent(Y, X).

descendant(X, Y) :-
    parent(Z, X),
    descendant(Z, Y).