(define $n-queen
  (lambda [$n]
    (match-all (between 1 n) (Multiset Integer)
      [<cons $a_1
             (loop $l $i (between 2 n)
                   <cons (loop $l1 $i1 (between 1 (- i 1))
                               (& ^,(- a_i1 (- i i1))
                                  ^,(+ a_i1 (- i i1))
                                  l1)
                               $a_i)
                         l>
                   <nil>)>
       [@(loop $l $i (between 1 n)  {a_i @l} {})]])))