;; question 1

;; check-duplicates : number nlon -> boolean
(define (check-duplicates n lst)
  (cond [(empty? lst) false]
        [else (or (= (first lst) n) 
                  (check-duplicates n (rest lst)))]))

;; last : nlon -> number
;; obtain last item of list
(define (last lst)
  (cond [(empty? (rest lst)) (first lst)]
        [else (last (rest lst))]))

;; remove-duplicates : nlon -> nlon
(define (remove-duplicates lst)
  (cond [(empty? (rest lst)) empty]
        [(check-duplicates (first lst) lst) (remove-duplicates (rest lst))]
        [(not (check-duplicates (first lst) lst)) 
         (cons (first lst) (remove-duplicates (rest lst)))]))