anchor.diff:                   (remove-nodes (rest nodes))))))
       (remove-nodes (rule-node-list rule))))
   
  -(defmethod successor-exists-p ((parent shared-node) (node node1))
  +(defmethod find-existing-successor ((parent shared-node) (node node1))
     (gethash (node1-test node) (shared-node-successors parent)))
   
  -(defmethod successor-exists-p (parent node)
  +(defmethod find-existing-successor (parent node)
     (declare (ignore parent node))
     nil)
   
  
positive.code: ;;; File: network-ops.lisp
  ;;; Description:
  
  ;;; $Id: network-ops.lisp,v 1.13 2002/10/08 18:17:27 youngde Exp $
  
  (in-package "LISA")
  
  
negative.code:            (merge-successors (parent successors)
               (if (endp successors) parent
                 (let* ((new-successor (first successors))
                        (existing-successor 
                         (find-existing-successor 
                          parent (successor-node new-successor))))
                   (cond ((null existing-successor)
                          (add-successor parent (successor-node new-successor)
                                         (successor-connector new-successor))
                          (add-node-set parent (successor-node new-successor)))
                         (t
                          (add-node-set parent (successor-node new-successor) t)
                          (merge-successors 
                           (successor-node existing-successor)
                           (shared-node-all-successors 
                            (successor-node new-successor)))))
                   (merge-successors parent (rest successors)))))
             (merge-root-node (new-root)
               (let ((existing-root
  