def split_to_and_since_delong(df):
    """Split the frame into time periods that DeLong analyzed and those since his article.
    :param df: The frame to split
    :return: Tuple with (to_delong, since_delong)
    """

    to_delong_index = [d for d in df.index if d.year <= 2004 and d.month < 6]
    since_delong_index = [d for d in df.index if d.year > 2004 or (d.year is 2004 and d.month >= 6)]
    return df.loc[to_delong_index], df.loc[since_delong_index]