def FermiFunctionSmallZ_(m, z):
    """
    Details about the expansion are in Mehran Kardar's notes at
    http://ocw.mit.edu/courses/physics/8-333-statistical-mechanics-i-statistical-mechanics-of-particles-fall-2013/lecture-notes/MIT8_333F13_Lec23.pdf
    """
    return (z - z ** 2 / 2 ** m + z ** 3 / 3 ** m - z ** 4 / 4 ** m + z ** 
        5 / 5 ** m - z ** 6 / 6 ** m)
