main:
        {((0 0) (0 1) (0 2)
        (0 3) (0 4) (1 0)
        (1 1) (1 2) (1 3)
        (1 4) (2 0) (2 1)
        (2 2) (2 3) (3 0)
        (3 1) (3 2) (4 0))

        { dup
        "A(" << { %d " " . << } ... ") = " <<
    reverse give
    ack
    %d cr << } ... }

ack!:
    { dup zero?
        { <-> dup zero?
            { <->
                cp
                1 -
                <- <- 1 - ->
                ack ->
                ack }
            { <->
                1 -
                <- 1 ->
                ack }
        if }
        { zap 1 + }
    if }

zero?!: { 0 = }