A set is usually represented by uppercase Latin letters, such as A, B and C, and the elements in the set are represented by lowercase Latin letters, such as A, B and C..
Latin letters are just the names of sets, which have no practical significance.
Natural language is not concise enough and easy to be imprecise, so it is generally used less.
The enumeration method is very simple, that is, the elements are listed one by one with braces.
Generally, graphic methods are used for set operations, including Wayne diagram, number axis and rectangular coordinate system.
Enumeration is a method of enumerating the elements of a collection one by one. For example, the three primary colors in optics can be represented by the set {red, green and blue}; The set A composed of four letters A, B, C and D can be represented by A={a, B, C, d}, and so on.
The description method is in the form of {representing element | satisfying attribute}.
Let the set S consist of all elements with a certain property p, then the set can be expressed by describing the common properties of the elements in the set: S={x|P(x)}. For example, the set b consisting of the square root of 2 can be expressed as B={x|x2=2}. Rational number and positive real number set can be expressed as sum, respectively.