def __rxor__(self, i):
        """Return self(i) when ``i`` is an int.

        Examples
        ========

        >>> p = Permutation(1, 2, 9)
        >>> 2 ^ p == p(2) == 9
        True

        """
        if int(i) == i:
            return self(i)
        else:
            raise NotImplementedError(
                f'i^p = p(i) when i is an integer, not {i}.')