pl-ail-files/exercise0.pl

   1 /* The facts about the Dutch Royal Family */
   2
   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).
  12
  13 father(hendrik, juliana).
  14 father(bernard, beatrix).
  15 father(bernard, christina).
  16 father(bernard, irene).
  17 father(bernard, margriet).
  18 father(claus, friso).
  19 father(claus, alexander).
  20 father(claus, constantijn).
  21 father(willem, wilhelmina).
  22
  23 queen(beatrix).
  24 queen(juliana).
  25 queen(wilhelmina).
  26 queen(emma).
  27 king(willem).
  28
  29 /* rules */
  30
  31 parent(X, Y) :- mother(X, Y).
  32 parent(X, Y) :- father(X, Y).
  33
  34 ruler(X) :- queen(X).
  35 ruler(X) :- king(X).
  36
  37 predecessor(X, Y) :-
  38    parent(X, Y),
  39    ruler(X),
  40    ruler(Y).
  41 predecessor(X, Y) :-
  42    ruler(X),
  43    parent(X, Z),
  44    predecessor(Z, Y).