[−1,∞),(0,∞)[-1, \infty),(0, \infty)[−1,∞),(0,∞)
{x∈R:x≥0},{x∈R:x≤0}\{x \in R: x \geq 0\},\{x \in R: x \leq 0\}{x∈R:x≥0},{x∈R:x≤0}
R,R\mathrm{R}, \mathrm{R}R,R
R,(−∞,0]R,(-\infty, 0]R,(−∞,0]
