Consider a,b) \to \left[(a-1)+10\times (b-1) +1\right] " alt="fa,b) \to \left[(a-1)+10\times (b-1) +1\right] " />

Then the smallest value takes is , and the largest is , the image of distinct elements of are distinct. Thus we have points in the range and points in the image, and the image is: .

Now turn this into a formal demonstration.

CB