Correspondence is used to describe the corresponding law or relationship between two or more objects. Correspondence can be direct, explicit, indirect and implicit. In the fields of mathematics, logic and statistics, correspondence is used to describe the relationship between variables, such as functional relationship. In mathematics, correspondence can refer to a function or a mapping to describe the relationship between input and output. Correspondence is a basic concept in mathematics and logic, which refers to a special relationship between two sets. There is a one-to-one correspondence between the elements of one set and the elements of the other set, which can be described by functions, maps or rules.