;Determines if a list is symmetric (returns true or false)
(define (symmetric ls)
  (define size (- (length ls) 1))
  (define middle (if (odd? size) (/ (- size 1) 2) (/ size 2)))
  (define (helper ref)
    (if (= middle ref) #t
        (if (eq? (list-ref ls ref) (list-ref ls (- size ref))) (helper (+ ref 1)) ())))
  (helper 0))

;Returns the sum of the numbers from a to b
(define (next a)
  (+ a 1);put whatever operation you want in here.
  )
(define (sum a b);sum integers from a to b
  (if (> a b)
      0
      (+ a (sum (next a) b))
      )
  )