'Generates the previous binary ordered subset.
Examples
>>> from sympy.combinatorics.subsets import Subset
>>> a = Subset([], [\'a\', \'b\', \'c\', \'d\'])
>>> a.prev_binary().subset
[\'a\', \'b\', \'c\', \'d\']
>>> a = Subset([\'c\', \'d\'], [\'a\', \'b\', \'c\', \'d\'])
>>> a.prev_binary().subset
[\'c\']
See Also
next_binary, iterate_binary'

def prev_binary(self):

    return self.iterate_binary((-1))
