def is_Singleton(self):
        """
        Checks to see if the permutation contains only one number and is
        thus the only possible permutation of this set of numbers

        Examples
        ========

        >>> Permutation([0]).is_Singleton
        True
        >>> Permutation([0, 1]).is_Singleton
        False

        See Also
        ========

        is_Empty

        """
        return self.size == 1