Thanks for the proof, it was fun to follow, and I agree that it's quite intuitive. I think that it would be helpful to mention why sqrt(y) must be an integer.

Thanks for the proof, it was fun to follow, and I agree that it's quite intuitive. I think that it would be helpful to mention why sqrt(y) must be an integer. (I know that it is, but it also feels a bit glossed over, given that all the other steps of the proof were explained so thoroughly.)