anchor.diff:    (let ((ev (first evs)))
       (if (belongs act ev)
   	(apply (fn-of ev)
  -	       (append (list act)
  +	       (append (list act (time-of ev))
   		       (if (slot-boundp ev 'args)
   			   (args-of ev))))
   	(error 'error-invalid))))
  
positive.code:   (setf (slot-value pt 'id)
  	(incf *fresh-port-id*)))
  
  (defun gettime ()
    *clock*)
  
  (defmethod initialize-instance :after ((ev event) &key)
    (setf (slot-value ev 'id)
  
negative.code: 	 (owner-path-of ev)))
  
  
  (defmethod schedule ((all-events list) at (fn function) (act actor)
  		     &rest args)
    (declare (time-type at))
    (let ((ev (apply 'make-instance
  		   'event
  		   ;; building arguments for make-instance:
  		   ;; if args is nil, leave slot unbound
  		   (append (list :time at
  				 :fn fn
  				 :owner-path (path act))
  			   (if (null args)
  			       nil
  			       (list :args args))))))
      (values (the list (sort-events (cons ev all-events)))
  	    (the actor (add-event act ev))
  	    (the event ev))))
  
  
  (defmethod add-event ((act actor) (ev event))
  