anchor.diff:  
   (defmethod access-port ((sim simulator) (in in-port) (obj object))
     "Contract: simulator in-port object -> (or simulator nil)
  -                                         (or unlock-event nil)
  +                                         (or event nil)
   
      Purpose: to retrieve the owner of in-port.
   
  
positive.code: 
  (defmethod access-port ((sim simulator) (out out-port) (obj object))
    "Contract: simulator out-port object -> (or in-port nil)
                                            (or unlock-event nil)
  
     Purpose: to retrieve the in-port connected to out.
  
  
negative.code: 	      (the event (lock-port in obj)))))
  
  
  (defmethod output ((sim simulator) (out out-port) (obj object))
    "Contract: simulator out-port object -> events
  
     Purpose: to create a new event that will call handle-input on the
  