R−{23}R-\left\{\frac{2}{3}\right\}R−{32}
R−{13}R-\left\{\frac{1}{3}\right\}R−{31}
R−{32}R-\left\{\frac{3}{2}\right\}R−{23}
R−{12}\mathrm{R}-\left\{\frac{1}{2}\right\}R−{21}
