R−{14}\mathbb{R}-\left\{\frac{1}{4}\right\}R−{41}
R−{−14}\mathbb{R}-\left\{-\frac{1}{4}\right\}R−{−41}
R−{13}\mathbb{R}-\left\{\frac{1}{3}\right\}R−{31}
R−{−13}\mathbb{R}-\left\{-\frac{1}{3}\right\}R−{−31}