ABSTRACT
You will be familiar with the idea of coordinates in the plane consisting of ordered pairs of numbers. You are used to plotting points such as (3, 2) and ( , )2 2− on coordinate axes on graph paper. Each of the numbers in such a coordinate pair comes from a set: when you plot graphs this set is usually the real numbers R. The set of all pairs of coordinates such as (3, 2) and ( , )2 2− is called R × R, meaning that the first number comes from the set R, as does the second number. The notation R2 is sometimes used for R × R. The Cartesian product generalizes this idea.
