% program predicate queen(X,Y) says that there is a queen in position (X,Y)

% each row contains exactly one queen
	1 { queen(X, Y) : number(Y) } 1 :- number(X).

% each column contains exactly one queen
	1 { queen(Y, X) : number(Y) } 1 :- number(X).

% no two queens occur in the same diagonal
	:- number(X;X+I;I;Y), queen(X, Y), queen(X + I, Y + I).
	:- number(X;X+I;I;Y;Y-I), queen(X, Y), queen(X + I, Y - I). 

% the sum of the weights of blocks that have queens is at most w
	[ queen(X,Y) : number(X;Y) = weight(blockwt(X,Y)) ] w.