% from University of Kentucky

1 { q(X, Y) : d(Y) } 1 :- d(X).
1 { q(Y, X) : d(Y) } 1 :- d(X).

:- d(X;X+I;I;Y), q(X,Y), q(X+I,Y+I).
:- d(X;X+I;I;Y;Y-I), q(X,Y), q(X+I,Y-I). 

d(1..queens).

#hide.
#show q(X,Y).