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