def filter_subreddits(subreddits, all_subreddits):
    """
    checks that the `subreddits` are present in `all_subreddits` and returns only those who do
    :param subreddits: the subreddits to check
    :param all_subreddits: the whitelist of subreddits
    :return: the `subreddits` in `all_subreddits`
    """
    all_subreddits_lower = [i.lower() for i in all_subreddits]
    return list(filter(lambda x: x.lower() in all_subreddits_lower, subreddits))