anchor.diff:  (defun expex-expr-setq (ex x)
     (with ((moved new-expr) (expex-args ex (cddr x)))
   	(values moved
  -		    `((%setq ,(second x) ,@new-expr)))))
  +			(list (expex-filter-setter ex `(%setq ,(second x) ,@new-expr))))))
   
   (defun expex-lambda (ex x)
     (with-temporary *expex-funinfo* (get-lambda-funinfo x)
  
positive.code:   (and (atom x)
         (string= "~E" (subseq (symbol-name x) 0 2))))
  
  ;; Have guest filter the arguments for whatever reason.
  (defun expex-filter-arguments (ex x)
    (mapcar (fn (funcall (expex-argument-filter ex) _))
  		  x))
  
negative.code:   (function-collector #'((fun args)))
  
    ; Callback to collect used variables.
    (argument-filter #'((var) var))
  
    (setter-filter #'((var) var))
  
    (plain-arg-fun? #'((var)))
  
  