def head_match(anaphor, antecedent):
    """ Compute whether the heads of two mentions match.

    Args:
        anaphor (Mention): A mention.
        antecedent (Mention): Another mention, preceding the anaphor.

    Returns:
        The tuple ('head_match', MATCH), where MATCH is True if the heads of
        the mentions match exactly (ignoring case), and False otherwise.
    """
    match = anaphor.attributes["head_as_lowercase_string"] == \
            antecedent.attributes["head_as_lowercase_string"]

    return "head_match", match