Four pages are indeed necessary for planar graphs:

At STOC 1986, Yannakakis proved that planar graphs have 4-page book embeddings (see for what this means), announced an example requiring 4 pages, but never published the example. Finally now Bekos et al. have provided detailed constructions for planar graphs requiring 4 pages.

Still lost in limbo: Unger's claim from 1992 that testing 3-page embeddability with fixed vertex ordering is polynomial.

A variant of the classic 15-puzzle, where the puzzle is coiled around a cylinder. Unlike the original, this version is solvable because of the extra connection between the first and sixteenth squares of the frame. YouTube:

A day's break in the strike has allowed us to open-source Coursebuilder, the tool we made to produce accessible web-based versions of lecture notes.
It takes in LaTeX, and outputs HTML pages and slideshows.

@luka "roof" is a "haček" or "caron", if that helps find components for you

It's the universal non-palindrome day! This is the only date consisting of nothing but zeroes and twos that is not a palindrome no matter how you write it!


Relish it, we won't have another one of these for 20,000 years

enjoyed this release:
V/A - Lovecraft Creatures (2020)
Cian Orbe Netlabel
lovecraft, horror, dark ambient, experimental, creatures, soundtrack, ninurta, yog-sothoth, chthonian, sub-niggurath, nyarlathotep

A: dns record
AA: battery
AAA: battery
AAAA: dns record

I'm not sure I've seen this puzzle before, and I really like it:

We have n keys and n boxes. Each key fits only one box. We shuffle the keys and put one in each box. Then we randomly break open 1≤k≤n boxes. What is the probability that we can unlock all the other boxes?

I've been thinking about the fact that an n×n square grid has as many cells as a triangular lattice with n triangles on each side.
Is there a nice continuous bijection between them? When n is odd, you can at least keep one line of symmetry throughout.

@christianp Nice. I wish there were a way to do the same at arXiv, but things are a bit too dense there.

What I use most often at arXiv does work at MathWorld though:

testing MathJax 

Aha, so it doesn't seem to be set up for the `\$$…\$\$` tokens, but does work with `\\(…\\)`. OK then.

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testing MathJax 


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