anchor.diff:  	      (cancel ()
   		(values nil nil)))
   	    (values (the in-port in)
  -		    (lock-port out obj))))))
  +		    (lock-port sim out obj))))))
   
   
   (defmethod access-port ((sim simulator) (in in-port) (obj object))
  
positive.code:   sim)
  
  
  (defmethod lock-port ((p port) (obj object))
    "Contract: port object -> events
  
     Purpose: to lock the port and decide when unlock it.
  
  
negative.code: 	(wait ()
  	  (setf (waiting-queue-of out)
  		(append (waiting-queue-of out)
  			(list sim)))
  	  (values nil nil))
  	(cancel ()
  	  (values nil nil)))
  