'Gets the binary ordered subset of the specified rank.
Examples
>>> from sympy.combinatorics.subsets import Subset
>>> Subset.unrank_binary(4, [\'a\', \'b\', \'c\', \'d\']).subset
[\'b\']
See Also
iterate_binary, rank_binary'

@classmethod
def unrank_binary(self, rank, superset):

    bits = bin(rank)[2:].rjust(len(superset), '0')
    return Subset.subset_from_bitlist(superset, bits)
