R−{12},R−{−12}R-\left\{\frac{1}{2}\right\}, R-\left\{-\frac{1}{2}\right\}R−{21},R−{−21}
R−{−12},R−{−12}R-\left\{-\frac{1}{2}\right\}, R-\left\{-\frac{1}{2}\right\}R−{−21},R−{−21}
R−{12},R−{12}\mathrm{R}-\left\{\frac{1}{2}\right\}, \mathrm{R}-\left\{\frac{1}{2}\right\}R−{21},R−{21}
R−{−12},R−{12}R-\left\{-\frac{1}{2}\right\}, R-\left\{\frac{1}{2}\right\}R−{−21},R−{21}