In mathematics, a set refers to a whole composed of some specific objects. These objects can be numbers, letters, symbols, etc. Or other collection. Collections are usually represented by capital letters, and there is no duplication between members. The members of a set can be finite or infinite. A set can be represented by a description, that is, by enumerating the elements in the set or giving the definitions of elements that meet certain conditions. For example, {1, 2,3,4,5} represents a set containing the number 1, 2,3,4,5, or {x | x is an integer, and 0 \u003c x \u003c 5} represents a set containing all integers between 0 and 5. The operations of a set include union, intersection, difference and complement. Union refers to the combination of all elements in two or more sets into a new set; Intersection refers to a set composed of elements in two sets; A difference set refers to the removal of elements from another set; A complementary set refers to a set of elements that do not belong to a specific set relative to a complete set. Set theory is a branch of mathematics that studies sets. It studies the properties, relationships, operations and mappings between sets. Set theory is widely used in mathematics and other disciplines, such as mathematical analysis, algebra, probability theory, computer science and other fields.