def format_authors(paper):
    """
    format_authors formats list of author fields to strings

    :param paper: dict of paper meta data
    :type paper: dict
    :return: string format of authors
    :rtype: str
    """
    authors = paper["authors"]
    if len(authors) > 2:
        author = authors[0]["name"].split(" ")[-1] + " et al."
    elif len(authors) == 2:
        author = (
            authors[0]["name"].split(" ")[-1]
            + " & "
            + authors[-1]["name"].split(" ")[-1]
        )
    else:
        author = authors[0]["name"].split(" ")[-1]

    year = f', {paper["year"]}'

    return author + year