R,R\mathrm{R}, \mathrm{R}R,R
R−{0},R\mathrm{R}-\{0\}, \mathrm{R}R−{0},R
R+,R−{0}\mathrm{R}^{+}, \mathrm{R}-\{0\}R+,R−{0}
R−{0},[−1,1]R-\{0\},[-1,1]R−{0},[−1,1]