1 /* The facts about the Dutch Royal Family */
3 mother
(wilhelmina
, juliana
).
4 mother
(juliana
, beatrix
).
5 mother
(juliana
, christina
).
6 mother
(juliana
, irene
).
7 mother
(juliana
, margriet
).
8 mother
(beatrix
, friso
).
9 mother
(beatrix
, alexander
).
10 mother
(beatrix
, constantijn
).
11 mother
(emma
, wilhelmina
).
13 father
(hendrik
, juliana
).
14 father
(bernard
, beatrix
).
15 father
(bernard
, christina
).
16 father
(bernard
, irene
).
17 father
(bernard
, margriet
).
19 father
(claus
, alexander
).
20 father
(claus
, constantijn
).
21 father
(willem
, wilhelmina
).
31 parent
(X
, Y
) :- mother
(X
, Y
).
32 parent
(X
, Y
) :- father
(X
, Y
).