(self, delta=1)
return Prufer.unrank(self.rank -delta, self.nodes)
Generates the Prufer sequence that is -delta before the current one.

        Examples
        ========

        >>> from sympy.combinatorics.prufer import Prufer
        >>> a = Prufer([[0, 1], [1, 2], [2, 3], [1, 4]])
        >>> a.rank
        36
        >>> b = a.prev()
        >>> b
        Prufer([1, 2, 0])
        >>> b.rank
        35

        See Also
        ========

        prufer_rank, rank, next, size
Generates the Prufer sequence that is -delta before the current one.
Generates the Prufer sequence that is - delta before the current one .
def prev(self, delta=1):
        """Generates the Prufer sequence that is -delta before the current one.

        Examples
        ========

        >>> from sympy.combinatorics.prufer import Prufer
        >>> a = Prufer([[0, 1], [1, 2], [2, 3], [1, 4]])
        >>> a.rank
        36
        >>> b = a.prev()
        >>> b
        Prufer([1, 2, 0])
        >>> b.rank
        35

        See Also
        ========

        prufer_rank, rank, next, size

        """
        return Prufer.unrank(self.rank -delta, self.nodes)
def prev ( self , delta = 1 ) : return Prufer . unrank ( self . rank - delta , self . nodes )