Dave Richeson

That was where this idea came from! bsky.app/profile/divb...

3D prints of a hyperbolic paraboloid

3D prints of a elliptic paraboloid

3D prints of slices of a hyperbolic paraboloid

I created some OpenSCAD code to print these slices/traces of surfaces for a multivariable calculus class. I wrote about it on my blog and included a link to my GitHub page with the code.
divisbyzero.com/2026/02/01/3...

That situation where you run into an acquaintance in the produce section of a grocery store. And then in the next aisle. And then the next one. And then the next one...

title of the Wikipedia article. You can enter as many words as you want (although, obviously, the fewer words, the better).

Game my daughter showed me: Redactle. Each game is a Wikipedia article with all non-filler words redacted. You type words at random. If you find a word in the article, it tells you, and all instances are unredacted (as well as related words such as plurals and -ing forms). The goal is to find the

Good idea! I *think* I've picked them all up

A photo of pushpins on the floor

An inauspicious start to the day: I dropped a full box of pushpins, and my office is now fully booby-trapped for the Home Alone burglars.

Good thing I don’t believe in omens or signs.

I'm excited for this new book by my friend and colleague John MacCormick! He's an amazing scholar and writer. I'm sure this will be great.

An n=7 dragon curve

An n=8 dragon curve

An n=9 dragon curve

Four tiled dragon curves

I printed four n=7th iterate dragon curves. You can fit two together to get n=8 dragon curve, and four together to get n=9 dragon curve. You can also fit them together in a way that tiles the plane.

Yeah! That would be neat.

I'm loving my Bambu printer and the software that controls it. It is so much easier and more reliable than my old (cheaper) one.

Space filling curves by divbyzero These are three approximations of space-filling curves—continuous curves in two dimensions that fill an entire square region. There are three examples here: the Peano curve, the Hilbert curve, and the...

I just uploaded these to Thingiverse, in case anyone wants to print them. www.thingiverse.com/thing:7283420

make a joke that, as a topologist, I printed two line segments and a circle.

A photo of a 3D printed Peano curve

A photo of a 3D printed Hilbert curve

A photo of a 3D printed Moore curve

A photo of all three showing their flexibility.

I've been playing with the new 3D printer I got over winter break (Bambu P2S). I designed and printed these three (approximate) space-filling curves: Peano's (blue), Hilbert's (purple), and Moore's (orange). The walls are 1 mm wide and 6 mm high, so they flex when you hold them. I was going to

I always find it so interesting how different classes of students can be. I walked into the first meeting of my 9:00 AM calculus class a few minutes early, expecting the usual room of sleepy students all on their phones. But they were almost all there, happily chatting with each other!

You should be able to see where my cursor is and the lighter "ghost text" it is offering me.

Oh, and just to clarify, if you type some math, it tries to fully autocomplete what it thinks you want. Here's an example where I typed
$\int_0^\pi \sin^2(x)\, dx= \int
And by pressing tab, it will insert the trig identity, integrate, and evaluate. Much more than just guessing \frac{}{} from \fr

I have only a rudimentary knowledge of regular expressions. But knowing they exist, I can ask ChatGPT to give me the regular expression for [whatever I need].

a table, for instance, deleting one & in each row), it will recognize that and just let me tab through the rest of them. Very, very convenient!

Lastly, unrelated to AI, VS Code lets you perform search and replace with regular expressions, which can be more powerful than the basic find-and-replace.

predict what you're trying to type. Sometimes it is really annoying, like when it is trying to complete my sentences (I don't want that!), but other times it will auto-complete your LaTeX (a real time-saver). Most relevant to your issue: when I start a repetitive process (like deleting a column in

Workshop + GitHub for all my documents. If you use GitHub Copilot in the sidebar to make changes to the document, VS Code clearly highlights what has been added and what will be removed, and you can accept or reject each change individually.

Also, it has inline suggestions (ghost text), which

asked the AI to generate text versions. I specifically said I wanted them to be identical. They were looking good, but when I converted a crepe recipe, which ended with suggested toppings, it appended a whole bunch of new suggestions!

Regarding LaTeX: this summer, I switched to VS Code + LaTeX

I've been experimenting with AI, and while there's a lot that is very cool and powerful, it is still unpredictable. You're right that it is dangerous to assume it will keep everything the same that you want to be the same. My favorite example of this was when I scanned in some paper recipes and

You know you are a mathematician when… you are invited to a holiday party at a fancy mansion, and you mostly take pictures of the beautiful tiling patterns in the wood floor!

A footnote from Copeland's book "The Essential Turing". It reads: "Proceedings of the London Mathematical Society, 42 (1936–7), 230–65. The publication date of ‘On Computable Numbers’ is sometimes cited, incorrectly, as 1937. The article was published in two parts, both parts appearing in 1936. The break between the two parts occurred, rather inelegantly, in the middle of Section 5, at the bottom of p. 240 (p. 67 in the present volume). Pages 230–40 appeared in part 3 of volume 42, issued on 30 Nov. 1936, and the remainder of the article appeared in part 4, issued on 23 Dec. 1936. This information is given on the title pages of parts 3 and 4 of volume 42, which show the contents of each part and their dates of issue. (I am grateful to Robert Soare for sending me these pages. See R. I. Soare, ‘Computability and Recursion’, Bulletin of Symbolic Logic, 2 (1996), 284–321.) The article was published bearing the information ‘Received 28 May, 1936.—Read 12 November, 1936.’ However, Turing was in the United States on 12 November, having left England in September 1936 for what was to be a stay of almost two years (see the introductions to Chapters 3 and 4). Although papers were read at the meetings of the London Mathematical Society, many of those published in the Proceedings were ‘taken as read’, the author not necessarily being present at the meeting in question. Mysteriously, the minutes of the meeting held on 18 June 1936 list ‘On Computable Numbers, with an Application to the Entscheidungs- problem’ as one of 22 papers taken as read at that meeting. The minutes of an Annual General Meeting held [...]"

The continuation of a footnote from Copeland's book "The Essential Turing". It reads: "[...] on 12 Nov. 1936 contain no reference to the paper. (I am grateful to Janet Foster, Archives Consultant to the London Mathematical Society, for information.)"

For what it's worth, I tangled with the same year-of-publication question until I came across this (fascinating!) footnote in Copeland's book "The Essential Turing", and it sounded authoritative enough for me to take it as gospel.

Thanks for the information and conversation! The funny thing is, I had 1936 in the blog post. But yesterday, before I shared the link, I went to the journal's website and saw 1937, so I changed it! I appreciate your sleuthing. I'll change it back! londmathsoc.onlinelibrary.wiley.com/doi/abs/10.1...

Years ago (15?) I must have written my name and email address somewhere, and someone typed it as "Dale" instead of "Dave." It is interesting to observe the waves of Dale-email I get when some spammer buys that list of addresses. I hadn't for a while until a week or so ago, and now I'm flooded again.

Turing’s topological proof that every written alphabet is finite Recently one of my colleagues was reading Alan Turing’s groundbreaking 1936 article “On Computable Numbers with an Application to the Entscheidungsproblem.” This is the article in…

Here's an old blog post I wrote about a footnote in Turing's 1937 article "On computable numbers with an application to the Entscheidungsproblem," in which he gave a topological argument that any alphabet must be finite. divisbyzero.com/2010/05/27/t...

YouTube video by Jonatan Nielavitzky 3D Printed Difference Engine

Super-ambitious project by Jonatan Nielavitzky: a 3D printed Babbage Difference Engine! He says it's a work-in-progress but it looks pretty polished to me.

Show him some appreciation on youtube if you have a moment! (I'm trying to encourage him to keep going)

www.youtube.com/watch?v=NvOR...

Nonfiction A Walk in the Park: The True Story of a Spectacular Misadventure in the Grand Canyon—Kevin Fedarko Hero of Two Worlds: The Marquis de Lafayette in the Age of Revolution—Mike Duncan Dark Wire: The Incredible True Story of the Largest Sting Operation Ever—Joseph Cox Major Labels: A History of Popular Music in Seven Genres—Kelefa Sanneh The Gotti Wars: Taking Down America's Most Notorious Mobster—John Gleeson The Cuckoo's Egg: Tracking a Spy Through the Maze of Computer Espionage—Clifford Stoll Careless People: A Cautionary Tale of Power, Greed, and Lost Idealism—Sarah Wynn-Williams When the Clock Broke: Con Men, Conspiracists, and How America Cracked Up in the Early 1990s—John Ganz Fiction Martyr!—Kaveh Akbar I'm Starting to Worry About This Black Box of Doom—Jason Pargin The Briar Club—Kate Quinn Precipice—Robert Harris Pompeii—Robert Harris Nightshade—Michael Connelly The Quiet Librarian—Allen Eskens Fortune Favors the Dead (and others from this series)—Stephen Spotswood Listen for the Lie—Amy Tintera Several Dick Francis books that are on Spotify

My year in books: Goodreads said I read 49 books in 2025. However, six were DNFs (a record for me in one year?). As in previous years, I gravitated toward novels, but it is the nonfiction books that really stuck with me. Here are my favorite reads of the year, in no particular order.

When you open it, it turns into a Mobius band