anchor.diff:  
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  +;;; Uniquify webs.
  +;;;
  +;;; Make sure that every lexical location in a program corresponds to
  +;;; a unique web.
  +
  +(defun uniquify-webs (program)
  +  (let ((*program* program))
  +    ;; Recall that the web sets computed by COMPUTE-WEB-SETS is a list
  +    ;; that has as many elements as there are lexical locations in the
  +    ;; program.  Each element of the top-level list is a set of webs
  +    ;; represented as a list, all concerning the same lexical
  +    ;; location.  We uniqify all but one (the first) web in the list.
  +    (mapc (lambda (web-set)
  +	    (unless (null (cdr web-set))
  +	      (touch program 'instruction-graph))
  +	    (mapc #'uniquify-web (cdr web-set)))
  +	  (compute-web-sets program)))
  +  nil)
  +
  +(set-processor 'unique-webs 'uniquify-webs)
  +
  +(add-dependencies 'unique-webs
  +		  '(predecesors
  +		    procedures
  +		    instruction-ownership))
  +
  +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  +;;;
   ;;; Do some initial transformations.
   
   (defun initial-transformations (program)
  +  (make program 'unique-webs)
     (make program 'no-redundant-temporaries)
     (make program 'no-error-successors)
     (make program 'simplified-instructions)
  
positive.code: 
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Compute Webs.
  ;;;
  ;;; Two DU-chains are said to INTERSECT if and only if:
  ;;;
  
negative.code: 	  (extract-one-web du-chains)
  	(cons web (chains-to-webs rest)))))
  
  (defun compute-web-sets (program)
    (let ((du-chains (compute-du-chains program))
  	(webs '()))
      (loop until (null du-chains)
  