Christian Lawson-Perfect @christianp@mathstodon.xyz

I've just released a simple #ActivityPub debugging tool. It's hosted on Glitch so you don't have to worry about spinning up servers or SSL certs etc. You clone your own copy of the project, set it up, and you can create ActivityPub accounts that can send any raw JSON payload you specify to its followers. I use it for testing new and novel ActivityPub objects, and to test compatibility with messages sent from remote servers without needing to create an account on them.

https://tinysubversions.com/notes/activitypub-tool/

Concatenation of numbers preserves divisibility, that is if \(a_1,\dots,a_n\) are all divisible by d, then their concatenation \(a_1a_2\dots a_n\) is also divisible by d.

Also while I'm picking on Wiley, how did the following paper ever pass peer review for their journal _Concurrency and Computation, Practice and Experience_ (or even a basic sanity check that it has a coherent topic that fits the mission of the journal? https://doi.org/10.1002/cpe.5484

Puzzle problem: Suppose \(A_1, A_2, \ldots, A_n\) are finite sets, and each \(A_i\) contains an odd number of elements. Prove that there is a set \(S\subseteq \left\{1, 2, \ldots, n\right\}\) such that \(\displaystyle\sum_{i\in S} \left|A_i \cap A_j\right|\) is odd for every \(j\in \left\{1, 2, \ldots, n\right\}\).

The surprising link between recreational math and undecidability (https://blogs.scientificamerican.com/roots-of-unity/the-surprising-link-between-recreational-math-and-undecidability/): Evelyn Lamb describes how a seemingly isolated fact about Fibonacci numbers (\(F_n^2\vert F_m \Rightarrow F_n\vert m\)) led to Matiyasevich's solution to Hilbert's 10th problem, that there is no general algorithm for solving Diophantine equations.

non mathematicians: i hate math because i hate numbers

me, a mathematician: what the frick is a number

3D Hilbert curve stained glass triptych done!

‪Braiding gears. Three gears are linked in a chain, but you can “braid” them, rearranging how they connect to each other. Full video at https://youtu.be/Lh7yAbw0H24

seed phrase: Magpie Horse Pheasant Kudu Porcupine (HQ: http://aka-san.halcy.de/quasi/389717597.gif )

writing my homework in extremely dense mathematical notation to punish the professor for assigning it

another view, colours adjusted with darktable

Today's task: I'm thinking of some loophole to make this abuse of notation somehow valid