#| BEGIN (Write your solution here) |#
(define empty-board '())

(define (safe? k positions)
  (let ((row-k (car positions))
        (rest (cdr positions)))
    (define (check diag-dist others)
      (cond ((null? others) #t)
            ((or (= row-k (car others))
                 (= (abs (- row-k (car others))) diag-dist))
             #f)
            (else (check (+ diag-dist 1) (cdr others)))))
    (check 1 rest)))

(define (adjoin-position new-row k rest-of-queens)
  (cons new-row rest-of-queens))
#| END |#