anchor.diff:              (apply #'c2mop:ensure-class-using-class
                      (ignore-errors (find-class name)) name args)))))))
   
  -(defun stop-metap-ensure-class (origin)
  +(defun disable-metap (origin)
     #+sbcl
     (sb-ext:without-package-locks
       (setf (symbol-function 'c2mop:ensure-class) origin))
  
positive.code:   (:export :*metap-m1-m2-pairs*
             :register-m1-m2-pair
             :validate-superclass*
             :with-metap-ensured))
  (in-package :metap)
  
  
negative.code:     `(let ((,origin #'c2mop:ensure-class))
         (unwind-protect
              (progn
                (enable-metap)
                (progn ,@body))
           (disable-metap ,origin)))))
  