anchor.diff:  (defmethod cp-form ((form ast-return-from))
     (setf (value form) (cp-form (value form))
           (info form) (cp-form (info form)))
  +  (flush-mutable-variables)
     form)
   
   (defmethod cp-form ((form ast-setq))
  
positive.code:   (cond ((eql (go-tag-use-count (first (first (statements form)))) 1)
           (setf (second (first (statements form)))
                 (cp-form (second (first (statements form)))))
           (flush-mutable-variables)
           (setf (rest (statements form))
                 (loop
                    for (go-tag statement) in (rest (statements form))
                    collect (list go-tag (cp-form statement)))))
          (t
           (flush-mutable-variables)
           (setf (statements form)
                 (loop
                    for (go-tag statement) in (statements form)
                    collect (list go-tag (cp-form statement))))))
    form)
  
  (defmethod cp-form ((form ast-the))
  
negative.code: 
  (defmethod cp-form ((form ast-go))
    (setf (info form) (cp-form (info form)))
    (flush-mutable-variables)
    form)
  
  (defmethod cp-form ((form ast-if))
  