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