The set of positive integers and 0 is also called a natural number, usually denoted as n, and the set of all positive integers is called a positive integer set, denoted as N*, Z+ or N+. The set of all negative integers is called the set of negative integers, and is denoted as Z-.
Other mathematical symbol sets:
1, r: set of real numbers (including rational numbers and irrational numbers);
2.R+: positive real number set;
3.R-: negative real number set;
4. Q: Rational number set;
5.Q+: positive rational number set;
6.Q-: set of negative rational numbers;
7、? : an empty set (a set without any elements);
8.c: complex set.