anchor.diff:  
   (defmethod unlock-port ((sim simulator) (out out-port))
     "Contract: out-port -> events"
  -  (assert (lock-of out) nil "Unlocking a not locked port!")
     (setf (lock-of out) nil)
     (list (make-instance 'event
   		       :owner sim
  
positive.code: 		       :args (list p))))
  
  
  (defmethod unlock-port ((sim simulator) (in in-port))
    "Contract: out-port -> events"
    (assert (lock-of in) nil "Unlocking a not locked port!")
    (setf (lock-of in) nil)
    (let ((waiting (pop (waiting-queue-of in))))
      (when waiting
  
negative.code:                 unlock.
                  Specialize this method to provide your own lock
                  policy."
    (setf (lock-of p) t)
    (list (make-instance 'event
  		       :owner sim
  