1, n: non-negative integer set or natural number set {0, 1, 2,3, ...}.

2, N* or N+: positive integer set {1, 2, 3, …}.

3, z: integer set {…,-1, 0, 1, …}.

4. Q: Rational number set.

5.Q+: the set of positive rational numbers.

6.Q-: set of negative rational numbers.

7.r: set of real numbers (including rational numbers and irrational numbers).

8.R+: positive real number set.

9.R-: negative real number set.

10, c: complex set.

1 1、? An empty set (a collection without any elements).

Set the basics:

Set (abbreviated as set) is a basic concept in mathematics, which was put forward by Cantor. It is the research object of set theory, and the basic theory of set theory was not founded until 19 century. The simplest statement is that in the most primitive set theory-naive set theory, a set is "a bunch of things". The "things" in a set are called elements. If x is an element of set a, it is recorded as x ∈ a.

Collection is to bring together some definite and distinguishable objects in people's intuition or thinking to make them a whole (or monomer). This whole thing is a set. Those objects that make up a set are called elements of this set (or simply elements). Modern mathematics also uses "axioms" to define sets. The most basic axiom is, for example, Zemelo-Franco: For any set S 1 and S2, S 1=S2 If and only if there is a ∈S 1 for any object A, then A ∈ S2; If a∈S2, then a∈S 1.

There is an axiom that a set exists in disorder: for any object A and B, there is a set S, so that S has exactly two elements, one is object A and the other is object B, which was put forward by zermelo-fraenkel. The disorder formed by them is unique to the set, and is recorded as {a, b}. Since A and B are any two objects, they can be equal or not. When a=b, {a, b}, which can be recorded as or, is called a unit set. Axiom of the existence of empty sets: there is a set without any elements.