(−∞,0)(-\infty, 0)(−∞,0)
(0,∞)(0, \infty)(0,∞)
(−∞,0)∪(0,∞)(-\infty, 0) \cup(0, \infty)(−∞,0)∪(0,∞)
(1,∞)(1, \infty)(1,∞)
(−∞,∞)(-\infty, \infty)(−∞,∞)