anchor.diff:  (defmethod compute-slots ((class std-class))
     (std-compute-slots class))
   
  +(defmethod compute-slots :around ((class std-class))
  +  (let ((effective-slots (call-next-method)))
  +    (std-compute-slot-layouts class effective-slots)
  +    effective-slots))
  +
   (defgeneric compute-effective-slot-definition (class name direct-slots))
   (defmethod compute-effective-slot-definition ((class std-class) name direct-slots)
     (std-compute-effective-slot-definition class name direct-slots))
  
positive.code:                      #'std-compute-class-precedence-list
                       #'compute-class-precedence-list)
                   class))
    (setf (class-slots class)
          (funcall (if (std-class-p (class-of class))
                       #'std-compute-slots
                       #'compute-slots)
                   class))
    (let* ((instance-slots (remove-if-not 'instance-slot-p
                                          (class-slots class)))
           (layout (make-array (length instance-slots))))
  
negative.code: (defmethod reinitialize-instance :before ((class built-in-class) &rest args)
    (error "Cannot reinitialize built-in classes."))
  
  ;;; Structure-class.
  
  (defclass structure-class (clos-class)
  