@Glorfindel This edit seemed a bit unusual to me: mathoverflow.net/posts/43754/revisions Specifically, replacing the Wikipedia link by Wayback Machine link.
Of course, I can understand that it might be useful to have the version at the time when the question was posted. But if I was considering adding such link, I would probably opted for the specific revision on Wikipedia rather than for Wayback Machine.
But I'm not sure that this was the intention here.
@Glorfindel Yes, you're right. When I go to revision 1, I get the same error (Bad Title).
Before I posted here, I looked only at the current revision - I clicked on your Wayback Machine link and then tried to remove the "Wayback" part from the URL.
My bad for assuming that the original link and the last part of the Wayback Machine link were the same.
We all know that the Rubik's Cube provides a nice concrete introduction to group theory. I'm wondering what other similar gadgets are out there that you've found useful for introducing new math to undergraduates and/or advanced high school students.