anchor.diff:      :initform "simulated object"
       :accessor description-of
       :type string
  -    :documentation "Description of this object.")
  -
  -   (effects
  -    :initform ()
  -    :accessor effects-of
  -    :type list
  -    :documentation "Set of events this object is causing.")))
  +    :documentation "Description of this object.")))
   
   
   (defclass event (identifiable)
  
positive.code:   (:use :common-lisp)
    (:export :!transform :clone :run :next :prev
  	   :identifiable :id-of
  	   :simulated :description-of :effects-of
  	   :event :time-of :causes-of :!action-of
  	   :world :hystory-of :events-of))
  
  
  
negative.code:     :reader time-of
      :type fixnum
      :documentation "When this event must be executed.")
  
     (!action
      :initarg :!action
  