% Proseminar Programmiersprachen - Prolog
% Beispielprogramm
%
% written by Johannes Weissl

% Familienbeziehungen bei den Simpsons
female(marge).
female(lisa).
female(maggie).
male(grandpa).
male(homer).
male(bart).
parent(grandpa,homer).
parent(homer,bart).
parent(homer,lisa).
parent(homer,maggie).
parent(marge,bart).
parent(marge,lisa).
parent(marge,maggie).


% Die Loesung des Raetsels
same_gender(X,Y) :- female(X), female(Y).
same_gender(X,Y) :- male(X), male(Y).

follow(A,B,[A,B|_]).
follow(A,B,[_|T]) :- follow(A,B,T).

unique([H|T]) :- not(member(H,T)), unique(T).
unique([]).

solve(X) :-
    X = [A,B,C,D],
    parent(D,C),
    same_gender(D,B),
    female(A),
    follow(lisa,Z,X),
    male(Z),
    Z \= bart,
    B \= grandpa,
    unique(X).