Puzzles that ask you to do something that can't be done are annoying, even if the answer is simple. I prefer being challenged to do something that is possible but also difficult. That's a real challenge. None of this "prove that it can't be done" nonsense - I stopped doing that crap when I left High School, thankyaverymuch. No need to spend long times typing out a proof like that above when you could spend your time doing more productive and mind-challenging problems that actually have a solution. Proofs wore the most boring thing about Calculus by a long, long way. I don't care how much intelligence is required, I much prefer a sense of achievement in proving something can be done than proving something can't be done. Give us a real puzzle!