R−{4}R-\{4\}R−{4}
R−{−12}\mathrm{R}^{}-\left\{-\frac{1}{2}\right\}R−{−21}
R−{−4}R-\{-4\}R−{−4}
R−{12}\mathrm{R}-\left\{\frac{1}{2}\right\}R−{21}