(define (stat-set)
  (let ((internal-set (list)))
    (let ((current-max 0))
      (let ((current-min 0))
        (let ((current-length 0))
          (let ((current-average 0))
            (define (empty)
              (empty? internal-set)
              )
            (define (insert n)
              (set! internal-set
                    (append (list n) internal-set))
              (update)
              )
            (define (delete n)
              (set! internal-set (delete-helper n internal-set))
              (update)
              )
            (define (element? n)
              (define (element-helper n set)
                (cond ((null? set)
                       #f)
                      ((= n (car set))
                       #t)
                      (else
                       (element-helper n (cdr set))))
                )
              (element-helper n internal-set)
              )
            (define (largest)
              current-max
              )
            (define (smallest)
              current-min
              )
            (define (size)
              current-length
              )
            (define (average)
              current-average
              )
            (define (update)
              (set-largest)
              (set-smallest)
              (set-length)
              (set-average)
              )
            (define (set-largest)
              (define (max-help list)
                (cond ((null? (cdr list))
                       (car list))
                      ((< (car list) (max-help (cdr list))) (max-help (cdr list)))
                      (else (car list)))
                )
              (set! current-max (max-help internal-set))
              )
            (define (set-smallest)
              (define (min-help list)
                (cond ((null? (cdr list)) (car list))
                      ((< (car list) (min-help (cdr list))) (car list))
                      (else (min-help (cdr list))))
                )
              (set! current-min (min-help internal-set))
              )
            (define (set-length)
              (set! current-length (length internal-set))
              )
            (define (set-average)
              (define (sum list)
                (if (null? list)
                    0
                    (+ (car list) (sum (cdr list))))
              )
              (set! current-average (/ (sum internal-set) current-length))
              )
            (lambda (method)
              (cond ((eq? method 'empty?) empty)
                    ((eq? method 'insert) insert)
                    ((eq? method 'delete) delete)
                    ((eq? method 'element?) element?)
                    ((eq? method 'largest) largest)
                    ((eq? method 'smallest) smallest)
                    ((eq? method 'size) size)
                    ((eq? method 'average) average))))))))
  )