anchor.diff:  ;;; implementation, a common AI planning problem. The monkey's objective is to
   ;;; find and eat some bananas.
   
  -;;; $Id: mab-clos.lisp,v 1.6 2001/05/24 19:55:45 youngde Exp $
  +;;; $Id: mab-clos.lisp,v 1.7 2001/05/31 19:13:56 youngde Exp $
   
   (in-package "LISA-USER")
   
   (use-default-engine)
   
  -(defclass monkey ()
  +(defclass mab-fundamental () ())
  +
  +(defclass monkey (mab-fundamental)
     ((location :initarg :location
                :initform 'green-couch)
      (on-top-of :initarg :on-top-of
  
positive.code:    (holding :initarg :holding
              :initform 'nothing)))
  
  (defclass thing ()
    ((name :initarg :name)
     (location :initarg :location)
     (on-top-of :initarg :on-top-of
  
negative.code:    (weight :initarg :weight
             :initform 'light)))
  
  (defclass chest (mab-fundamental)
    ((name :initarg :name)
     (contents :initarg :contents)
     (unlocked-by :initarg :unlocked-by)))
  
  (defclass goal-is-to (mab-fundamental)
    ((action :initarg :action)
     (argument-1 :initarg :argument-1)
     (argument-2 :initarg :argument-2
  