(define difference
  (lambda (numbers)
    (if (null? numbers)
        0
        (- (car numbers) (difference (cdr numbers))))))

(define new-difference
  (lambda (numbers)
    (new-difference-helper (car numbers) (cdr numbers))))

(define new-difference-helper
  (lambda (difference-so-far remaining)
    (if (null? remaining)
        difference-so-far
        (new-difference-helper (- difference-so-far (car remaining))
                               (cdr remaining)))))