def tetrate(a, tetrate_acc):
        assert is_valid_other(a), "not a valid other"
        assert is_valid_accumulator(tetrate_acc), "not a valid accumulator"
        assert a > 0, "we don't define 0↑↑b"

        exponentiate_acc = xmpz(1)
        for _ in count_down(tetrate_acc):
            multiply_acc = xmpz(1)
            for _ in count_down(exponentiate_acc):
                add_acc = xmpz(0)
                for _ in count_down(multiply_acc):
                    for _ in range(a):
                        add_acc += 1
                multiply_acc = add_acc
            exponentiate_acc = multiply_acc
        return exponentiate_acc

    fn tetrate(a: u32, acc: &mut BigUint) {
        assert!(a > 0, "we don’t define 0↑↑b");

        let mut exp = BigUint::from(1u32);
        for () in acc.count_down() {
            let mut mul = BigUint::from(1u32);
            for () in exp.count_down() {
                let mut add = BigUint::ZERO;
                for () in mul.count_down() {
                    for _ in 0..a {
                        add += 1u32;
                    }
                }
                mul = add;
            }
            exp = mul;
        }
        *acc = exp;
    }

    If our only goal is to run forever, the solution is immediate:

    ```rs
    fn main() {
        loop {}
    }
    ```