def is_func_argument(i, clue):
    """
    Returns True if clue sub-part i is the argument of a directional function (like 'ana_r' or 'sub_l').

    We do this because insertion always happens after other functions have been resolved.
    """
    return (i > 0 and '_r' in clue[i - 1][1]) or (i < len(clue) - 1 and '_l' in clue[i + 1][1])