anchor.diff:  
   ;;;; SYMBOLS
   
  -(defvar *expexsym-counter* 0)
  +(defvar *expexsym-counter* nil)
   
   ;; Returns new unique symbol.
   (defun expex-sym ()
  -  (setf *expexsym-counter* (+ 1 *expexsym-counter*))
  -  (make-symbol (string-concat "~E" (string *expexsym-counter*))))
  +  ($ '~E (1+! *expexsym-counter*)))
   
   ;;;; GUEST CALLBACKS
   
  
positive.code:         (list x))
  	  (expex-make-%setq ex '~%ret x)))
  
  (defun expex-make-setq-copy (ex x s)
    (? (eq s (second x.))
       x
       `(,x.
  
negative.code: 			   (? (%setq? last.)
  				  (? (eq s (second last.))
  				     (expex-guest-filter-setter ex last.)
  				     (expex-copy-%setq ex last s))
  				  (expex-make-%setq ex s last.)))
  		x)))
  
  