Hello,

    I try to use the new feature: derived slot.   Everything is fine, except
an error is raised when try to drop the instance.
    It is raised by following code:

(defmethod slot-makunbound-using-class ((class persistent-metaclass)
(instance persistent-object) (slot-def derived-index-slot-definition))
  "Unbinding cannot be performed explicitly.  It is effectively
   inhibited when the derived fn says 'no'"
  (error "Cannot unbind derived slot values for ~A in class ~A"
     (slot-definition-name slot-def) (class-name class)))

   I want to know the suitable way to delete the instance using derived
slot.
   If I change above method to what indexed-slot-definition does, no error
is reported.

Thanks
Quan
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