The point is that, in my estimation, the statement in the footnote is a good exercise (provided that you don’t already know it, that it’s not immediately obvious to you, and that you’re still into set theory enough to know what countability and the diagonal argument are). I was initially tempted to just leave it as such, but then thought I’d provide the solution under a spoiler.
Thanks for clarifying. I'm not that young anymore, but I haven't seen this sort of spoiler tagging since forever (assuming that I ever saw it), so I just really didn't know what was going on. Maybe a simple reference to ROT13 at the beginning of your spoiler would have helped.
