def mark(l, h, idx):
    """Produce markers based on argument positions
    
    :param l: sentence position of first word in argument
    :param h: sentence position of last word in argument
    :param idx: argument index (1 or 2)
    """
    return [(l, "{}{}".format('~~[[', idx)), (h+1, "{}{}".format(idx, ']]~~'))]