anchor.diff:  			   (? (%setq? last.)
   				  (? (eq s (second last.))
   				     (expex-guest-filter-setter ex last.)
  -				     (expex-make-setq-copy ex last s))
  +				     (expex-copy-%setq ex last s))
   				  (expex-make-%setq ex s last.)))
   		x)))
   
  
positive.code: 
  ;;;; SYMBOLS
  
  (defvar *expexsym-counter* 0)
  
  ;; Returns new unique symbol.
  (defun expex-sym ()
    (setf *expexsym-counter* (+ 1 *expexsym-counter*))
    (make-symbol (string-concat "~E" (string *expexsym-counter*))))
  
  ;;;; GUEST CALLBACKS
  
  
negative.code: 
  (defun expression-expand (ex x)
    (when x
      (with-temporary *expexsym-counter* 0
  	  (with-temporary *current-expex* ex
  	    (with-temporary *expex-funinfo* (transpiler-global-funinfo *current-transpiler*)
            (expex-body ex x))))))
  