clpfd - n-queens solution not working in Prolog -


i trying run following code n-queens problem‍​..how far can go? find solutions n-queens problem: 

generate([],_). generate([h|t],n) :- h in 1..n , generate(t,n). lenlist(l,n) :- lenlist(l,0,n). lenlist([],n,n). lenlist([_|t],p,n) :- p1 p+1 , lenlist(t,p1,n).  queens(n,l) :-         generate(l,n),lenlist(l,n),         safe(l),!,         labeling([ffc],l).  notattack(x,xs) :- notattack(x,xs,1). notattack(x,[],n). notattack(x,[y|ys],n) :- x #\= y,                          x #\= y - n,                          x #\= y + n,                          n1 n + 1,                          notattack(x,ys,n1).  safe([]). safe([f|t]) :- notattack(f,t), safe(t).

i have swi-prolog installed on debian-9 (stable) linux , running above using command "swipl -f nqueens.pl". on loading, error: 

syntax error: operator expected (probably on 2nd code line)

where problem , how can solved? help.

the question mentions writting in clpfd (a constraint logic programming tool on finite domains). have import library:

:- use_module(library(clpfd)).  generate([],_). generate([h|t],n) :- h in 1..n , generate(t,n). lenlist(l,n) :- lenlist(l,0,n). lenlist([],n,n). lenlist([_|t],p,n) :- p1 p+1 , lenlist(t,p1,n).  queens(n,l) :-         generate(l,n),lenlist(l,n),         safe(l),!,         labeling([ffc],l).  notattack(x,xs) :- notattack(x,xs,1). notattack(x,[],n). notattack(x,[y|ys],n) :- x #\= y,                          x #\= y - n,                          x #\= y + n,                          n1 n + 1,                          notattack(x,ys,n1).  safe([]). safe([f|t]) :- notattack(f,t), safe(t).

then works, , produces instance:

?- queens(5,l). l = [1, 3, 5, 2, 4] ; l = [1, 4, 2, 5, 3] ; l = [2, 4, 1, 3, 5] ; l = [2, 5, 3, 1, 4] ; l = [3, 1, 4, 2, 5] ; l = [3, 5, 2, 4, 1] ; l = [4, 1, 3, 5, 2] ; l = [4, 2, 5, 3, 1] ; l = [5, 2, 4, 1, 3] ; l = [5, 3, 1, 4, 2].

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