anchor.diff:           (error "You can only use FSETF if you are modfifying a container.  I don't have a place to set when given ~A." place) )
           (t (let ((nth-arg (container-arg-n place)))
                (unless nth-arg
  -               (error "I can't figure out which argument is the container in ~A." place) )
  +               (error "I can't figure out which argument is the container in ~A."
  +                      place ))
                (find-container (nth nth-arg place)) ))))
   
   ;; <<>>=
  
positive.code:   (cond ((atom expr) nil)
          ((eql (first expr) 'modf-eval) nil)
          (t expr) ))
  
  ;; <<>>=
  (defun modf-expand (new-val expr form)
  
negative.code:                            expr form ))))))
                (nth (container-arg-n expr) expr)
                enclosed-obj-sym )))))
  
  ;; <<>>=
  (defmacro modf (place value &rest more)
  