public function rationalDiv(NI $a, NI $b)
    {
        list($a, $b) = $this->checkRationalTypes($a, $b);
        $n = $this->intMul($a->numerator(), $b->denominator());
        $d = $this->intMul($a->denominator(), $b->numerator());

        return RationalTypeFactory::create($n, $d);
    }