R−{2}R-\{2\}R−{2}
R−{−2,2}R-\{-2,2\}R−{−2,2}
R−{−3,1}\mathrm{R}-\{-3,1\}R−{−3,1}
R−{1,3}\mathrm{R}-\{1,3\}R−{1,3}