The mathematical symbol sets are n, N+, z, q, r, c and so on. The set of all non-negative integers is usually called the set of non-negative integers (or the set of natural numbers), and is marked as n; the set excluding 0 from the set of non-negative integers is also called the set of positive integers, and is marked as N+ (or N*). The set of all integers is usually called the integer set, and is denoted as z.

The set of all rational numbers is usually referred to as the set of rational numbers, which is denoted as Q. The set of all real numbers is usually referred to as the set of real numbers, which is denoted as R. The set of complex numbers is denoted as C. 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.

In the simplest way, defined by 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 called X ∈ A. A set is a collection of certain and distinguishable objects in human intuition or thinking.

Make it a whole or a single body, and the whole is a collection. Those objects that make up a set are called elements of this set (or simply elements). Symbol set: empty set is recorded as subset, ST is recorded as ST; The intersection point is marked as A∩B or B∩A, and marked as AuB.