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Which regular polytopes have their vertices a subset of other regular polytopes in the same dimension (cp4space.hatsya.com/2020/10/01)? We don't know! The answer is closely connected to the existence of Hadamard matrices (en.wikipedia.org/wiki/Hadamard), which are famously conjectured to exist in dimensions divisible by four. A solution to the Hadamard matrix existence problem would also solve the polytope problem.

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Ombre et lumière. #art

Two different LaTeX styles:

- Inline $$\int x^2 dx = \frac{1}{3}x^3+c.$$

- Display $\int x^2 dx = \frac{1}{3}x^3+c.$

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How combinatorics became legitimate (igorpak.wordpress.com/2019/04/): Igor Pak recommends two interesting video interviews with László Lovász and Endre Szemerédi. The whole interviews are quite long but they're broken into 10-minute clips and Igor has picked out the ones relevant to the title.

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Anyone know of pre-2001 references for the (trivial) fact that all finite posets can be represented as the poset of divisibility of a finite set of integers? I tried MathOverflow (mathoverflow.net/q/329910/440) but they weren't very helpful, preferring either to complain about how trivial it was or to explain to me why it's true instead of giving me references.

The reason is that I think I'm using the wrong reference for a minor point in a Wikipedia article and want to use a better one.

A tiny rehash of some Rosetta Code [1] yields the Rain Dragon Bow. Source file was named dra.go 🙃

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