A binary group consisting of two elements in a certain order is called an ordered pair, which is expressed as

Let a and b be two sets, called set a, B = {

Kargi

Let A and B be two nonempty sets, and let any subset R of A and B be a binary relation from A to B, which is called relation for short. Where A is called the front domain of relation R, B is called the back domain of relation R, and if A = B, R is called the binary relation on A..

Let R be a binary relation from A to B, then A is the front domain of relation R, and B is the back domain of relation R ... Order:

C = {x|x ∈ A，？ y ∈ B，& ltx，y & gt∈ R}，D = {y|y ∈ B，？ X ∈ A,<x, y>∈ R}. Call c the domain of R, and write it as C = domR；; D is the range of r, and it is recorded as D = ranR；; FldR = domR ∪ ranR is the domain of R.

A relationship is a special set, so two basic representations of a set (enumeration and narration) can be used.

The performance of the relationship.

Take a look, after all, there is no exam ... to be honest, it feels useless! ! ! ! I can't learn these in foreign textbooks. Just have an impression and get to know the relationship. A large part of the algorithm is to solve the relationship problem. I mainly want to learn graph theory.