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I've been seeing a flood of new names, refugees from Twitter. I've been a refugee from Livejournal and Google+, so I know what that's like.

I'm a CS professor, working in algorithms, graphs, and geometry. I also blog and edit Wikipedia. My posts here include links on mathematics, computing, and academic politics, and to my blog, Wikipedia articles, papers, and occasional photos. If you post mathy stuff or I know you elsewhere, I'm likely to follow back; you're also welcome to lurk.


"The University of Idaho administration has abandoned its duty to uphold the mission of the institution and signaled to all the world that the university is no longer committed to academic freedom", according to The American Association of University Professors at

The context is a memo sent out by the university's lawyers requesting faculty to "remain neutral on the topic of abortion"; for more on that, see and

Corruption in old images stored in Google Photos:, via

Let this be a reminder that if you care about the permanence and stability of your data, keep a safe copy on media you own and control, not on someone else's machine on the cloud somewhere.

Ultralightweight pavilion made from woven bamboo strips, aided by modern computer modeling:

Not very good for keeping sun or rain off in the form shown, but I imagine one could stretch a membrane over it if that were the goal.

The strange Wiki-history of Sethahedra and Chestahedra:, via and

The Chestahedron has 4 equilateral triangles and 3 kites of equal area. A bronze sculpture is at

The Sethahedron is a nonexistent variation with golden-ratio dimensions. If made of paper it will fold along kite diagonals to form ten faces.

The promoter of the 2nd has been edit-warring to keep their erroneous version in Wikipedia.

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@ngons Proposed definition: \(\textit{Foxagon}\) – A hexagon with exactly one line of reflective symmetry and one reflex angle.

Publication laundering ( How "proceedings journals" that accept whole special-issues without any internal oversight over relevance or quality ease the collaboration among academics desperate for publications, middlemen who sell authorship slots on mass-produced junk, and big publishers hungry for that publication-fee and subscription-fee cash as long as they can point the blame elsewhere. James Heathers, via

Mutilated chessboard problem:

Remove opposite corners from a chessboard and try to cover the rest with dominos. It's just planar bipartite perfect matching, easy for algorithms. There's a cute trick for human problem solving that I won't spoil. And yet, a logical formulation has been a test case for automated reasoning for nearly 60 years, and is provably hard for some systems (especially resolution). How can it be so easy and so hard? New Wikipedia Good Article.

More stories on BoingBoing and the Guardian

The statement in the Guardian from a book-banning spokesperson "This book series has not been banned, and they remain available in our libraries" appears to actually mean that the ban blocked students from reading the books but failed to remove them permanently from the libraries, and that they became available because the ban was rescinded.

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"Girls Who Code" appears on this year's list of books banned by US schools:

Apparently this happened not directly because the kind of people who ban books want women to be ignorant, but rather because these books appeared on a diversity resource list and the kind of people who ban books oppose diversity (meaning anything that would challenge the white cis male evangelical-Christian point of view) in all forms. Fortunately local protests got the ban rescinded.

The new math of wrinkling,

_Quanta_ on the research of Ian Tobasco on the way that crumpling thin surfaces (like paper) can sometimes lead to disordered folds and sometimes lead to regular patterns, like Yoshimura buckling (, depending in part on local curvature. The _Quanta_ article links Tobasco's 2021 paper ( but neglects to link the newer paper it highlights; it is,

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Do you need another demonstration that the physics of liquids is strange and counterintuitive? I learned from that, if you have the kind of peanut butter that needs mixing, but is too liquid (swimming in extra peanut oil), you can make it thicker by mixing in a little bit of water. The water droplets in the oil make an emulsion that is thicker than either the water or oil would be by themselves. I had occasion to try it recently and it worked! Science strikes again.

New blog post: Counting paths in convex polygons,

A simple coloring-based explanation for why there are exactly \(n2^{n-3}\) non-crossing paths through all points of an \(n\)-gon, and exactly \(\tfrac{n}{4}(3^{n-1}+3)\) through some of the points (counting a single point as a path).

Irish librarians protest ( as Wiley suddenly removes over 1300 ebooks from the existing subscription packages of academic libraries, in order to convert them to a fee-per-student individual-textbook subscription model. Via

Descriptive combinatorics and distributed algorithms,

Nice survey article by Anton Bernshteyn in _Notices of the AMS_ about implications and in some cases equivalences between topological statements about whether certain infinite sets are Borel or measurable, and whether certain corresponding finite computational problems have distributed algorithms with sub-logarithmic round complexity.

Terry Tao on his new preprint with Rachel Greenfeld, "A counterexample to the periodic tiling conjecture":,

The Schmitt-Conway-Danzer biprism and Socolar–Taylor tile ( tile \(\mathbb{R}^3\) and \(\mathbb{R}^2\times{}\)finite only aperiodically. The einstein problem ( asks if \(\mathbb{R}^2\) has an aperiodic tile. This work looks at analogous questions for tiling by translation of \(\mathbb{Z}^d\).

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@11011110 look you might be interested:

Found cyclography in an old Hungarian descriptive geometry book, and coded and had much fun with it. Now, I think I have the origin, Wilhelm Fiedler.

Pictures: cube and octahedron

Ed Pegg constructs and visualizes Engel's 38-sided space-filling polyhedron (the most possible for a Voronoi cell of an isohedral Voronoi tessellation) surrounded by 38 copies of itself:

The exciting new world of AI prompt injection:, via

Promote your business by running a bot that uses other people's social media post text to prompt a text-writing AI that generates customized responses to those posts. What could go wrong?

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