def post_process_weird(system_mentions):
    """ Removes all mentions which are "mm", "hmm", "ahem", "um", "US" or
    "U.S.".

    Args:
        system_mentions (list(Mention): A list of system mentions.

    Returns:
        list(Mention): the filtered list of mentions.
    """
    return sorted(
        [mention for mention
         in system_mentions
         if " ".join(mention.attributes["tokens"]).lower() not in
         ["mm", "hmm", "ahem", "um"]
         and " ".join(mention.attributes["tokens"]) != "US"
         and " ".join(mention.attributes["tokens"]) != "U.S."]
    )