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