FILTERP
=LAMBDA(p,
    LAMBDA(xs,
        FILTER(xs, p(xs))
    )
)


INITS
=LAMBDA(s,
    MID(
        s,
        1, SEQUENCE(
            1, 1 + LEN(s),
            0, 1
        )
    )
)


LASTCOL
=LAMBDA(xs,
    IF(AND(1 = COLUMNS(xs), ISBLANK(xs)),
        NA(),
        INDEX(xs, 1, COLUMNS(xs))
    )
)


TAILCOLS
=LAMBDA(xs,
    IF(1 < COLUMNS(xs),
        INDEX(
            xs,
            1,
            SEQUENCE(1, COLUMNS(xs) - 1, 2, 1)
        ),
        NA()
    )
)