Failed to converge when add conditional range

[bink24]

Hi @adam-hanna , I have a question regarding the variable fn.
Is it possible to add conditional range as following code?

var fn = (x, y, z) => {
    x = z - y + (
        z >= 0 && z <=  10000 ? 10 : (
            z >= 10001 && z <= 20000 ? 20 : 0
        )
    )
}

I tried, it always return "failed to converge".
Thanks.