'Returns if the group is Abelian.
Examples
>>> from sympy.combinatorics.free_groups import free_group
>>> f, x, y, z = free_group("x y z")
>>> f.is_abelian
False'

@property
def is_abelian(self):

    if ((self.rank == 0) or (self.rank == 1)):
        return True
    else:
        return False
