anchor.diff:  
      Description: specialize lock-port to provide a lock / unlock policy
                   for the in-port."
  -  (if (busy-p-of in)
  +  (if (lock-of in)
         (restart-case (error 'in-port-busy)
   	(wait ()
   	  (setf (waiting-queue-of in)
  
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:   ((id
      :reader id-of
      :type id-type)
     (lock
      :initarg :lock
      :initform nil
      :accessor lock-of
      :type boolean)
     (waiting-queue
      :initform (list)
      :accessor waiting-queue-of
      :type list
      :documentation "List of sims waiting to use this port")))
  
  
  (defclass in-port (port)
  