anchor.diff:      (let ((old-superclasses (mapcar #'class-name (mopu:direct-superclasses user-class))))
         `(unwind-protect
               (progn
  -              (define-user-class ,class-sym ,new-superclasses)
  +              (set-user-class ',class-sym ',new-superclasses)
                 ,@body)
  -         (define-user-class ,class-sym ,old-superclasses)))))
  +         (set-user-class ',class-sym ',old-superclasses)))))
   
   (declaim (ftype (function ((or symbol function))) method-combination-name))
   (defun method-combination-name (fun)
  
positive.code: NAME must be an existing class.
  NAME is automatically appended to SUPERCLASSES, so that 'user-NAME' inherits
  from NAME last."
    (let ((user-name (user-class-name name))
          (superclasses-with-original (remove-duplicates
                                       (append superclasses (list name)))))
      `(progn
         (export-always ',user-name (symbol-package ',user-name))
         ;; Probably no need to call the defclass macro if we just need to
         ;; set the superclasses.
         (closer-mop:ensure-class ',user-name
                                  :direct-superclasses ',superclasses-with-original
                                  :documentation (documentation ',name 'type)))))
  
  (defun user-class-p (class-specifier)
    (not (mopu:direct-slot-names class-specifier)))
  
  (defmacro with-user-class ((class-sym new-superclasses) &body body) ; TODO: Export if users ever demand it.
    "Dynamically override the superclasses of the user class corresponding to
  
negative.code:                              (declare (ignorable %slot-default%))
                               ,(cadr slot))
                             (call-next-method))))
         (set-user-class ',name ',(cons temp-name
                                        (mapcar #'class-name
                                                (mopu:direct-superclasses final-name)))))))
  
  (defun get-initform (class-symbol class-slot)
    (getf (mopu:slot-properties (find-class class-symbol) class-slot) :initform))
  