'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'

def prev(self, delta=1):

    return Prufer.unrank((self.rank - delta), self.nodes)
