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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sunrise_sunset(ephemeris, topos):
 """Build a function of time that returns whether the sun is up. The function that this returns will expect a single argument that is a :class:`~skyfield.timelib.Time` and will return ``True`` if the sun is up, else ``False``. """

    sun = ephemeris['sun']
    topos_at = (ephemeris['earth'] + topos).at

    def is_sun_up_at(t):
        """Return `True` if the sun has risen by time `t`."""
        t._nutation_angles = iau2000b(t.tt)
        return topos_at(t).observe(sun).apparent().altaz()[0].degrees > -0.8333

    is_sun_up_at.rough_period = 0.5  # twice a day
    return is_sun_up_at