• A crowdsourced project to link erdosproblems.com with OEIS (\(\mathbb{M}\), see also), launched by Thomas Bloom and Terry Tao.

  • WeakC4, or distilling an emergent object (\(\mathbb{M}\), livestream). A project to compress a search-free strategy for winning Connect 4 into as few bits as possible, by storing a game graph for a small opening book of nodes combined with an efficient encoding of simple winning strategies at the leaves of the graph. So far they are down to 9221 nodes and roughly 150kbytes. See also their visualization of the opening book graph.

  • New Good Article on Wikipedia: Pythagorean addition (\(\mathbb{M}\)). This is the operation of computing the hypotenuse of a right triangle from its two sides. Because this is commutative and associative, it defines a commutative monoid, and Knuth defined it as a built-in binary operation in metafont, writing that it could likely replace most uses of square roots in software.

    Back when people used slide rules instead of computers, some slide rules had special scales (positioning numbers by their square roots rather than their logs) that would allow them to perform this calculation, for instance in converting from Cartesian to polar coordinates: see “Find absolute value” on p.3 of this slide-rule instruction guide.

    Nowadays most programming language libraries provide this operation as hypot.

  • Problematic new licensing requirements from Springer journals: you are forbidden from including any post-submission improvements in your openly-licensed preprints, must add a disclaimer to the preprints saying they are unimproved, are forbidden from creating any later version that makes changes to the format or content of the Springer-published version, and are not given any opportunity to object to or modify the terms of the license.

  • Somehow cleveref is broken despite not having been updated in 7 years, after a LaTeX kernel change from November 2024 was included in recent TeXlive updates. A workaround using aliascnt may be possible, if you are not using amsmath (!) and have control over when cleveref is loaded.

  • Right kite reptile tessellations, Dani Laura. The right kite with side ratio \(\sqrt2\) lets the tiles fit together particularly nicely, with some larger sides bisected by smaller sides of tiles.

  • Wikipedia is getting rid of its mobile specific subdomain (\(\mathbb{M}\)), and there was much rejoicing.

  • What is the minimum number of faces in a polyhedron all of whose faces are non-convex (\(\mathbb{M}\))? My answer is an eight-sided hexagonal torus credited by Grünbaum and Szilassi to a 1988 German diploma thesis of Schwörbel, modified to reduce its face count to seven. But it does not fit some definitions of polyhedra, because it has pairs of faces with disconnected intersections.

  • Fraudulent publishing in the mathematical sciences (\(\mathbb{M}\), via): part I of a report of a joint committee of IMU and ICIAM consisting of Ilka Agricola, Lynn Heller, Wil Schilders, Moritz Schubotz, Peter Taylor, and Luis Vega. Part I is “where are we now” and part II (to come) is “what can we do”. I saw Agricola speak on this sort of thing a year ago and she tells a compelling story about how fraudulent publishing practices (by both publishers and authors) are damaging mathematics.

  • The recent unpleasantness over Poland is already causing me minor repercussions here in California (\(\mathbb{M}\)): my coauthor doesn’t want to risk flying to Warsaw, a potential repeat of this happening, and getting stranded there. So he has canceled his travel to ESA / ALGO to present our joint paper on bandwidth and BFS. Instead it will be presented as a prerecorded video.

    I guess Europeans traveling to ALGO can always count on taking a train instead, a little more reliably than air travel to Warsaw after recent events, so I hope a dent in intercontinental attendees doesn’t hurt the conference too much. Anyway, best wishes to all in attendance, and of course to all in Poland and Ukraine who have more significant consequences to worry about.

  • In a “McCarthy era move”, UC Berkeley gives Trump administration 160 names of students and faculty investigated for “alleged antisemitic incidents” (\(\mathbb{M}\), see also, archived). The Guardian quotes one of the targeted scholars, Judith Butler: “We have a right to know the charges against us, to know who has made the charges and to review them and defend ourselves. But none of that has happened, which is why we’re in Kafka-land … It is an enormous breach of trust.” They added that “the university’s normal procedures for handling complaints had been suspended, which has seemingly stripped faculty of their rights to respond to claims or get basic information about the inquiries”.

  • Matroid bingo (\(\mathbb{M}\)). The requirements that no bingo card be empty, that everyone can win (no card has a subset of numbers of another card), and that no two players can win simultaneously (no union of two cards has a third card as a subset) turn out to match the axioms for the cycles in a matroid. It is not required that everyone have equal probability of winning, but the dual Fano matroid turns out to be particularly fair in this sense.

  • Wikipedia is resilient because it is boring (\(\mathbb{M}\), archived). Josh Dzieza, The Verge.