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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 valid_redditors(redditors, sub):
 """Return a verified list of valid Redditor instances. :param redditors: A list comprised of Redditor instances and/or strings that are to be verified as actual redditor accounts. :param sub: A Subreddit instance that the authenticated account has flair changing permission on. Note: Flair will be unset for all valid redditors in `redditors` on the subreddit `sub`. A valid redditor is defined as a redditor that is registered on reddit. """

    simplified = list(set(six.text_type(x).lower() for x in redditors))
    return [sub.reddit_session.get_redditor(simplified[i], fetch=False)
            for (i, resp) in enumerate(sub.set_flair_csv(
                ({'user': x, 'flair_text': x} for x in simplified)))
            if resp['ok']]