anchor.diff:      :initarg :owner
       :initform (error ":owner missing")
       :accessor owner-of
  -    :type simulator)
  -   (waiting-queue
  -    :initform (list)
  -    :accessor waiting-queue-of
  -    :type list
  -    :documentation "List of ids of the actors waiting to use this
  -    port")))
  +    :type simulator)))
   
   
   (defclass out-port (port)
  -  ((waiting-p
  -    :initform nil
  -    :accessor waiting-p-of
  -    :type boolean
  -    :documentation "True if the owner of this port is waiting in order
  -    to access it.")))
  +  nil)
   
   
   (defclass stream-in-port (in-port)
  
positive.code: 
     Description: specialize lock-port to provide a lock / unlock policy
                  for the out-port."
    (if (busy-p-of out)
        (restart-case (error 'out-port-busy)
  	(wait ()
  	  (setf (waiting-p-of out)
  		t)
  	  (values nil nil))
  	(cancel ()
  	  (values nil nil)))
  
negative.code: 
     Description: specialize lock-port to provide a lock / unlock policy
                  for the in-port."
    (if (lock-of in)
        (restart-case (error 'in-port-busy)
  	(wait ()
  	  (setf (waiting-queue-of in)
  