anchor.diff:  ;;; File: node2-exists.lisp
   ;;; Description:
   
  -;;; $Id: node2-exists.lisp,v 1.1 2002/11/18 15:59:33 youngde Exp $
  +;;; $Id: node2-exists.lisp,v 1.2 2002/11/18 17:55:01 youngde Exp $
   
   (in-package "LISA")
   
  
positive.code:                                       (left-tokens remove-token))
    (loop for right-token being the hash-value 
        of (join-node-right-memory self)
        do (when (and (test-tokens self left-tokens right-token)
                      (zerop (token-decrement-exists-counter left-tokens)))
             (pass-tokens-to-successor 
              self (combine-tokens left-tokens right-token)))))
  
  
negative.code:                                       (left-tokens add-token))
    (loop for right-token being the hash-value 
        of (join-node-right-memory self)
        do (when (test-tokens self left-tokens right-token)
             (token-increment-exists-counter left-tokens)
             (pass-tokens-to-successor 
              self (combine-tokens left-tokens right-token)))))
  
  