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.
Update 1: sum of two prime numbers =99.
What is the product of these two prime numbers? (I'm not wrong)
1. The sum of two prime numbers is 99. W