Hi everyone!

I am struggling a bit with a question, it is pretty basic, and I have read through this part in the book, I just don't quite understand how this works.

Question:

Suppose that A = {1, 2, 3} and B = {1, 2}. Let R be the relation from A to B containing (a, b) if a is inside of A, b is inside of B, and a > b. What is the matrix representing R if a_{1}= 0 , a_{2}= 2, and a_{3}= 3 and b_{1}= 1 and b_{2}= 2?

In the book they do give a matrice as a solution, but they don't explain how they got the matrice. So, I was hoping someone could explain to me how to think about this.

Thank you all for reading!