Linkage

Octagonally symmetric fractal tile (via). It tiles the plane with two incompatible square tiling lattices, rotated \(45^\circ\) with respect to each other.

The computational power of the Digi-Comp II, a mechanical device in which marbles roll downhill flipping toggles. At JCDCG³, Matt Johnson spoke on the complexity analysis of Turing Tumble, another closely related marble-race computing device.

The celebrity, the paparazzo and the bodyguards (G+). Greg Egan explains how finitely many point guards can block visibility between two points in a mirrored room, as shown by Emily Riehl based on a puzzle posed by Maryam Mirzakhani.

Abstracts from the Japan Conference on Discrete and Computational Geometry, Graphs, and Games as a Google-drive PDF file. More complete versions of the papers should eventually become available through a volume of Springer LNCS.

EU prepares to approve licensing fees for all web links to news sites, and dubiously-reliable copyright takedown filters for all user-uploaded web content (G+). Spoiler: they voted yes.

Trouble at Nutrients (G+, via). The resigning editorial board complained “that the publisher, the Multidisciplinary Digital Publishing Institute (MDPI), pressured them to accept manuscripts of mediocre quality and importance.” The former editor in chief calls himself naive for “assuming he would be able to lead a high-quality open-access journal owned by a commercial publisher”.

Stable line crosser. This new Game of Life pattern can send a glider across a diagonal line of live cells, and then repair the damage to the line of cells and return to its original state.

Lenore Blum tells us why she resigned from CMU. She makes the point that, although allegations of sexual assault by prominent people are justifiably making headlines lately, “sexism in the workplace … affects many, many more women” and must also be resisted.

Proceedings of the 26th International Symposium on Graph Drawing and Network Visualization (G+). Graph Drawing uses an unusual hybrid open-access arXiv-overlay publication model where all authors upload the conference proceedings versions of their papers to arXiv, the conference publishes a collection of links to these versions as the “online proceedings”, and then later everything is published again through Springer LNCS. This is the arXiv version of this year’s proceedings.

Securing the Vote. The National Academy of Sciences tells us what we should already have known, but it helps to repeat it: Use paper ballots, conduct random risk-limiting audits, and avoid internet voting unless/until much stronger security guarantees exist.

Isosceles triangle. Now a Good Article on Wikipedia. Plenty of other similarly basic Wikipedia articles could still use similar improvement.

A new solution to Euler’s Königsberg Bridge Problem. Robert Bosch draws a picture of Königsberg and its seven bridges as an Eulerian graph on the points of a grid. One of many impressive pieces of mathematical art in the Bridges 2018 gallery.

No intrinsic gender differences in children’s earliest numerical abilities (G+). Relevant for a recent fuss about the odd and disputed publication history of a paper by Ted Hill suggesting a mathematical explanation for how genetic differences in variance might be differentially advantageous for men vs women. These supposed differences have historically been used as an excuse for failure to improve gender ratios in mathematics. But if they don’t exist, there’s nothing to model and no basis for the excuse. See also Gowers’ criticism of the mathematical modeling in Hill’s paper and an earlier post linking at the top to contradictory claims on what happened with Hill’s paper (on which I am too unsure of the truth to express an opinion).