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