def mknj2i(item):
    """
    Transforms "mknj" notation into tensor index order for the ERI.
    Args:
        item (str): an arbitrary transpose of "mknj" letters;

    Returns:
        4 indexes.
    """
    notation = "mknj"
    notation = dict(zip(notation, range(len(notation))))
    return tuple(notation[i] for i in item)