private function getTypePairing(NumericTypeInterface $a, NumericTypeInterface $b)
    {
        $search = [
            'Chippyash\Type\Number\Rational\\',
            'Chippyash\Type\Number\Complex\\',
            'Chippyash\Type\Number\\',
            'Type'
        ];
        $replace = ['', '', '', ''];
        $tA = strtolower(str_replace($search, $replace, get_class($a)));
        $tB = strtolower(str_replace($search, $replace, get_class($b)));

        return "{$tA}:{$tB}";
    }