anchor.diff:    (with-output-as-presentation
         (pane object (presentation-type-of object))
       (print object)))
  +
   (defmethod inspect-object ((object symbol) pane)
     (inspector-table
       (format pane "Symbol ~S" (symbol-name object))
  
positive.code:     ((slot 'settable-slot :gesture :select :prompt "Set slot"))
    (setf (slot-value (car slot) (cdr slot))
  	(accept t :prompt "New slot value")))
  
negative.code: 
  
  (define-presentation-type settable-slot ()
    :inherit-from t)
  (define-presentation-type cons ()
    :inherit-from t)
  
  (define-presentation-method present (object (type settable-slot) 
  