(define (contains l x)
    (cond
        ((null? l) #f)
        ((eq? (car l) x) #t)
        (else (contains (cdr l) x))))

(define (length lis)
   (cond ((null? lis)
          0)
         (else
          (+ 1 (length (cdr lis))))))

(define (reverse1 l)
  (if (null? l)
     nil
     (append (reverse1 (cdr l)) (list (car l)))
  )
)

(define (modulo a b)
  (if (< a b) a (modulo (- a b) b))
)

(define (get l)
  (if
    (= (modulo (length l) 2) 0)
    (car l)
    (car (reverse l)))
)

(get '(5 3 7))
(contains '(3 6 8 1) 8)