anchor.diff:  
   (defparameter *table*
     (make-instance 'table :id 0
  -		 :chairs (list (make-instance 'chair :id 0)
  -			       (make-instance 'chair :id 1)
  -			       (make-instance 'chair :id 2)
  -			       (make-instance 'chair :id 3))
  +		 :chairs (list (make-instance 'chair)
  +			       (make-instance 'chair))
   		 :persons (list (make-instance 'person
  -					       :id 0 :name "Geppo")
  +					       :name "Geppo")
   				(make-instance 'person
  -					       :id 1 :name "Claudia")
  +					       :name "Claudia")
   				(make-instance 'person
  -					       :id 2 :name "Peppo")
  +					       :name "Peppo")
   				(make-instance 'person
  -					       :id 3 :name "Verruca"))))
  +					       :name "Verruca"))
  +		 :events ()))
  
positive.code:     :documentation "List of persons.")))
  
  
  (defclass person (simulated)
    ((description
      :initform "a person")
  
     (name
  
negative.code:     :documentation "Name of this person.")))
  
  
  (defparameter *genid-chair* -1)
  
  (defclass chair (simulated)
    ((ds::id
      :initform (incf *genid-chair*))
  
     (ds::description
      :initform "a chair")
     
     (occupier
  