(self)
return Subset(ret_set, super_set)
Generates the previous lexicographically ordered subset.

        Examples
        ========

        >>> from sympy.combinatorics.subsets import Subset
        >>> a = Subset([], ['a','b','c','d'])
        >>> a.prev_lexicographic().subset
        ['d']
        >>> a = Subset(['c','d'], ['a','b','c','d'])
        >>> a.prev_lexicographic().subset
        ['c']

        See Also
        ========
        next_lexicographic
Generates the previous lexicographically ordered subset.
Generates the previous lexicographically ordered subset .
def prev_lexicographic(self):
        """
        Generates the previous lexicographically ordered subset.

        Examples
        ========

        >>> from sympy.combinatorics.subsets import Subset
        >>> a = Subset([], ['a','b','c','d'])
        >>> a.prev_lexicographic().subset
        ['d']
        >>> a = Subset(['c','d'], ['a','b','c','d'])
        >>> a.prev_lexicographic().subset
        ['c']

        See Also
        ========
        next_lexicographic
        """
        i = self.superset_size - 1
        indices = Subset.subset_indices(self.subset, self.superset)

        while i not in indices and i >= 0:
            i = i - 1

        if i - 1 in indices or i == 0:
            indices.remove(i)
        else:
            if i >= 0:
                indices.remove(i)
                indices.append(i - 1)
            indices.append(self.superset_size - 1)

        ret_set = []
        super_set = self.superset
        for i in indices:
            ret_set.append(super_set[i])
        return Subset(ret_set, super_set)
def prev_lexicographic ( self ) : i = self . superset_size - 1 indices = Subset . subset_indices ( self . subset , self . superset ) while i not in indices and i >= 0 : i = i - 1 if i - 1 in indices or i == 0 : indices . remove ( i ) else : if i >= 0 : indices . remove ( i ) indices . append ( i - 1 ) indices . append ( self . superset_size - 1 ) ret_set = [ ] super_set = self . superset for i in indices : ret_set . append ( super_set [ i ] ) return Subset ( ret_set , super_set )