interface Mul<A B> {
    _: Output
    fn Op.mul(A B) -> [Output]
}

impl Mul<*u64 *u64> {
    u64: Output
    fn Op.mul(*u64: a *u64: b) -> [u64] {
        a @ b @ *
    }
}

impl Mul<u64 *u64> {
    u64: Output
    fn Op.mul(u64: a *u64: b) -> [u64] {
        a b @ *
    }
}