vater_von(yoshihito, hirohito).
mutter_von(sadako, hirohito).
vater_von(kunioshi, nagako).
mutter_von(chikako, nagako).
vater_von(hirohito, akihito).
vater_von(hirohito, hitachi).
mutter_von(nagako, akihito).
mutter_von(nagako, hitachi).
grossvater_von(G,E) :- vater_von(G, V), vater_von(V, E).
grossvater_von(G,E) :- vater_von(G, M), mutter_von(M, E).
geschwister(X,Y) :- vater_von(V, X), vater_von(V, Y),
                    mutter_von(M, X), mutter_von(M, Y).
elter_von(X, Y) :- vater_von(X, Y).
elter_von(X, Y) :- mutter_von(X, Y).

?- mutter_von(sadako, hirohito).
?- mutter_von(sadako, sadako).
?- mutter_von(X, hirohito).
?- elter_von(X, akihito).
?- geschwister(Y, X).


--- Ergebnis: --------------------------------------------------------

?- mutter_von(sadako, hirohito).

Resolution 1: Yes.

Resolution 2: No.


?- mutter_von(sadako, sadako).

Resolution 1: No.


?- mutter_von(X{0}, hirohito).

Resolution 1: Yes.
X = sadako

Resolution 2: No.


?- elter_von(X{0}, akihito).

Resolution 1: Yes.
X = hirohito

Resolution 2: Yes.
X = nagako

Resolution 3: No.


?- geschwister(Y{0}, X{0}).

Resolution 1: Yes.
X = hirohito
Y = hirohito

Resolution 2: Yes.
X = nagako
Y = nagako

Resolution 3: Yes.
X = akihito
Y = akihito

Resolution 4: Yes.
X = hitachi
Y = akihito

Resolution 5: Yes.
X = akihito
Y = hitachi

Resolution 6: Yes.
X = hitachi
Y = hitachi

Resolution 7: No.