'Computes the binary ordered rank.
Examples
>>> from sympy.combinatorics.subsets import Subset
>>> a = Subset([], [\'a\',\'b\',\'c\',\'d\'])
>>> a.rank_binary
0
>>> a = Subset([\'c\', \'d\'], [\'a\', \'b\', \'c\', \'d\'])
>>> a.rank_binary
3
See Also
iterate_binary, unrank_binary'

@property
def rank_binary(self):

    if (self._rank_binary is None):
        self._rank_binary = int(''.join(Subset.bitlist_from_subset(self.subset, self.superset)), 2)
    return self._rank_binary
