anchor.diff:    (mark-variable varrec 0))
   
   (define-classify-variables (define varrec . val)
  -  (classify-variables-2 form)
  +  (classify-variables-recurse form)
     (mark-variable varrec 2))
   
   (define (classify-block-variables varrecs init form)
     (dolist (varrec varrecs)
       (varrec-attr-set! varrec 'state init))
  -  (classify-variables-2 form)
  +  (classify-variables-recurse form)
     (dolist (varrec varrecs)
       (varrec-attr-set! varrec 'written
                         (= 2 (varrec-attr-remove varrec 'state)))))
  
positive.code: 
  (define (comment-form-forms forms)
      (mapfor (form forms) (comment-form form)))
  (define (comment-form-2 form)
      (list* (car form) (cadr form) (comment-form-forms (cddr form))))
  (define-walker comment-form ())
  
  
negative.code: 
  (define internal-keywords '(let call ref make-box box-ref box-set!))
  
  (define all-keywords (append keywords-2 internal-keywords keywords-1))
  
  ;;; Transform a program so that every form begins with a
  ;;; distinguishing keyword:
  ;;;
  