It's not just that she used the Grandi's series, along with paradoxes regarding functions Euler treated in the eighteenth century. What troubled me the most is that she used negatives. I didn't teach negatives. I had been struggling for a month to make them grasp the concept of natural numbers and here, in front of me, I had a ten year old who was manipulating the concept of 'infinities' with a robustness that would make the entire Department of Physics at Courant shit their ...