anchor.diff:      :documentation "List of persons.")))
   
   
  +(defparameter *genid-person* -1)
  +
   (defclass person (simulated)
  -  ((description
  +  ((ds::id
  +    :initform (incf *genid-person*))
  +
  +   (ds::description
       :initform "a person")
   
      (name
  
positive.code: (in-package :tw)
  
  
  (defclass table (world)
    ((chairs
      :initarg :chairs
      :initform (error "missing :chairs")
      :accessor chairs-of
  
negative.code: 
  (defparameter *table*
    (make-instance 'table :id 0
  		 :chairs (list (make-instance 'chair)
  			       (make-instance 'chair))
  		 :persons (list (make-instance 'person
  					       :name "Geppo")
  				(make-instance 'person
  					       :name "Claudia")
  				(make-instance 'person
  					       :name "Peppo")
  				(make-instance 'person
  					       :name "Verruca"))
  		 :events ()))
  