def is_even(self):
        """
        Checks if a permutation is even.

        Examples
        ========

        >>> p = Permutation([0, 1, 2, 3])
        >>> p.is_even
        True
        >>> p = Permutation([3, 2, 1, 0])
        >>> p.is_even
        True

        See Also
        ========

        is_odd

        """
        return not self.is_odd