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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def set_restricted(self, obj, restricted):
 """Set the restriction on the given object. You can use this to signal that a certain function is restricted. Then you can query the restriction later with :meth:`Reftrack.is_restricted`. :param obj: a hashable object :param restricted: True, if you want to restrict the object. :type restricted: :class:`bool` :returns: None :rtype: None :raises: None """

        if restricted:
            self._restricted.add(obj)
        elif obj in self._restricted:
            self._restricted.remove(obj)