Chapter 5.1 relations

Define relations as sets of ordered pairs. This makes functions

Use letter rho ρ

ρ = { (1, 2),(2,4),(3,7),(2,2)}

A relation is a subset of the cartesian product of two setsx^2 + y^2 = 8

For the set of numbers{ -4 ... + 4} on each For all natural numbers or whatever there's an infinite number of pairs in the cartesian products