def preceding_token(mention):
    """ Compute the token preceding a mention.

    Args:
        mention (Mention): A mention.

    Returns:
        The tuple ('preceding', TOKEN), where TOKEN is the (lowercased) token
        preceding the mention. If no such token exists, set TOKEN to 'NONE'.
    """
    prec = mention.get_context(-1)

    if prec:
        return "preceding", prec[0].lower()
    else:
        return "preceding", "NONE"