anchor.diff:  (defun std-slot-boundp (instance slot-name)
     (multiple-value-bind (slots location)
         (slot-location-in-instance instance slot-name)
  +    (when (not location)
  +      (return-from std-slot-boundp
  +        (values (slot-missing (class-of instance) instance
  +                              slot-name 'slot-boundp))))
       (not (eq *secret-unbound-value* (slot-contents slots location)))))
   (defun slot-boundp (object slot-name)
     (let ((metaclass (class-of (class-of object))))
  
positive.code: (defun (setf std-slot-value) (value instance slot-name)
    (multiple-value-bind (slots location)
        (slot-location-in-instance instance slot-name)
      (setf (slot-contents slots location) value)))
  (defun (setf slot-value) (new-value object slot-name)
    (cond ((std-class-p (class-of (class-of object)))
  
negative.code:                         (class-slots class)
                          :key #'slot-definition-name)))
          (when (null slot)
            (return-from slot-location
              nil))
          (case (slot-definition-allocation slot)
            ((:instance :class)
             (slot-definition-location slot))
  