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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 check_video(video, languages=None, age=None, undefined=False):
 """Perform some checks on the `video`. All the checks are optional. Return `False` if any of this check fails: * `languages` already exist in `video`'s :attr:`~subliminal.video.Video.subtitle_languages`. * `video` is older than `age`. * `video` has an `undefined` language in :attr:`~subliminal.video.Video.subtitle_languages`. :param video: video to check. :type video: :class:`~subliminal.video.Video` :param languages: desired languages. :type languages: set of :class:`~babelfish.language.Language` :param datetime.timedelta age: maximum age of the video. :param bool undefined: fail on existing undefined language. :return: `True` if the video passes the checks, `False` otherwise. :rtype: bool """

    # language test
    if languages and not (languages - video.subtitle_languages):
        logger.debug('All languages %r exist', languages)
        return False

    # age test
    if age and video.age > age:
        logger.debug('Video is older than %r', age)
        return False

    # undefined test
    if undefined and Language('und') in video.subtitle_languages:
        logger.debug('Undefined language found')
        return False

    return True