fn even(n: u32) -> Bool {
    if n == 0 {
        return true
    }
    return odd(n - 1)
}

fn odd(n: u32) -> Bool {
    if n == 0 {
        return false
    }
    return even(n - 1)
}

pub fn main(world: World) -> Void raises {
    if even(10) && odd(9) {
        check world.out.write("mutual recursion ok\n")
    }
}