CHARS
=LAMBDA(s,
    MID(
        s,
        SEQUENCE(1, LEN(s), 1, 1),
        1
    )
)


INITCOLS
=LAMBDA(xs,
    INDEX(
        xs,
        SEQUENCE(
            1,
            COLUMNS(xs) - 1,
            1,
        )
    )
)


LASTCOL
=LAMBDA(xs,
    INDEX(
        xs,
        SEQUENCE(ROWS(xs), 1, 1, 1),
        COLUMNS(xs)
    )
)