Mark Dominus

I'm an expert computer programmer, looking for work. Check out my résumé: https://plover.com/~mjd/cv/Mark%20Jason%20Dominus.pdf

Also, an amateur mathematician, but not the angle-trisecting kind.

Good blog: https://blog.plover.com/
Crappy blog: https://shitpost.plover.com/
Math.SE: https://math.stackexchange.com/users/25554/mjd?tab=profile
Totemic animal spirit: Octopus

Public Key

npub1zfyhk2vwxl5cm5xjzyp409jd58fjs9jxzzhefdc0xlywtypna6ksgx8xdp

NIP-05 Address

mjd_at_mathstodon.xyz@momostr.pink

Profile Code

nprofile1qqspyjtm9x8r06vd6rfpzq6hjex6r5egzerpptu5ku8n0j89jqe7atgprpmhxue69uhhyetvv9ujumt0d4hhxarj9ecxjmntdqyp2j

Publishing to

relay.momostr.pink

Author Public Key

npub1zfyhk2vwxl5cm5xjzyp409jd58fjs9jxzzhefdc0xlywtypna6ksgx8xdp

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Last Notes

2026-05-19 17:23:08 UTC

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Credit: Puzzling Stack Exchange user “Florian F” https://puzzling.stackexchange.com/users/2136/florian-f
https://media.mathstodon.xyz/media_attachments/files/116/602/395/172/114/025/original/b334ce0bf9215fb7.png

2026-05-19 17:19:42 UTC

Let A and B be regular pentagons with side lengths 3 and 4. Is there a simple dissection of A and B into pieces that can form a regular pentagon with side length 5?
Edit: Yes, this thread gives several solutions with only 6 pieces each. https://puzzling.stackexchange.com/q/125649/21425

2026-05-10 11:06:41 UTC

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The explanation I got is that water itself is such a powerful solvent that if you drink distilled water it will tend to dissolve your insides. (Not instantly, of course.) Tap water doesn't do this (it was claimed) because it is already at its saturation limit for solutes.
The question I really want answered is: is it safe to drink deuterium oxide?

2026-05-03 18:30:28 UTC

#dodecahedron #dodecahedronDimanche
https://media.mathstodon.xyz/media_attachments/files/116/512/055/025/471/253/original/d9f03b744a6de2bc.jpeg

2026-05-01 12:24:30 UTC

A COMPUTER CANNOT FIND OUT
THEREFORE A COMPUTER MUST NEVER BE ALLOWED TO FUCK AROUND

2026-05-01 03:46:17 UTC

Looking for a beautiful and elegant background wallpaper for your phone or monitor? Try image search for “amniotic ferning”.
https://commons.wikimedia.org/wiki/File:Positive_fern_test.jpg
https://media.mathstodon.xyz/media_attachments/files/116/497/259/325/647/207/original/66007d1e9f9302b8.jpg

2026-04-28 16:32:53 UTC

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My kid pointed out that our holly tree has eyes, and now I can't unsee it.
https://media.mathstodon.xyz/media_attachments/files/116/483/290/439/581/853/original/5266789c98338f7a.jpg
https://media.mathstodon.xyz/media_attachments/files/116/483/290/448/507/334/original/d0ad8a7cb37c08d5.jpg

2026-04-27 08:38:36 UTC

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It works okay if the addition is all at the end! But if not, all those nice multiplications were completely wasted!

2026-04-27 08:31:50 UTC

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An interesting contrast with the representation of integers as lists of the exponents of their prime factors, where ×, gcd, lcm, and = are fast and easy, ≤ is doable, but it's of very limited use because + is impossible.

2026-04-27 08:27:04 UTC

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This reminds me of the observation that there's a representation of numeric quantities that can perform both addition and multiplication of numbers in constant time, but it's useless for numeric calculation because there's no corresponding algorithm for the ≤ relation.
(The representation being expression trees with numbers at the leaves.)

2026-04-26 12:39:17 UTC

“In 2023, Raytheon’s president stood at the Paris Air Show and described what it took to restart Stinger missile production. They brought back engineers in their 70s to teach younger workers how to build a missile from paper schematics drawn during the Carter administration.”
“The Pentagon hadn’t bought a new Stinger in twenty years. Then Russia invaded Ukraine, and suddenly everyone needed them. [But] the production line was shut down.”
“The software industry is in year three of the same optimization.”
https://techtrenches.dev/p/the-west-forgot-how-to-make-things

2026-04-12 14:31:01 UTC

View from my porch this week 🌸
#bloomScrolling #westPhiladelphia
https://media.mathstodon.xyz/media_attachments/files/116/392/207/903/543/493/original/6de2c2f1ef72a070.jpg

2026-04-06 14:53:26 UTC

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Then in 2011 those trolls the Dutch built seven bridges in one town that were all designed to look exactly like the imaginary banknote bridges. They even painted the bridges the same colors as the banknotes.
So now the EU banknotes depict the bridges of Spijkenisse, South Holland. (pop. 72,500)
https://media.mathstodon.xyz/media_attachments/files/116/358/321/339/806/879/original/c792901b4504f320.png

2026-04-06 14:50:26 UTC

In 1996, tired of squabbling between EU countries about whose favorite person or building should be on the EU banknotes, the currency commission held a competition for a new design: “The ground rules for the design strictly prohibited displaying any recognizable national monuments or heroes that risked giving greater prominence to one country over another.” The winning design was a series of bridges that were stylistically typical of different kinds of European bridges, but which weren't any specific bridges. For example:
https://media.mathstodon.xyz/media_attachments/files/116/358/748/571/598/082/original/eb08f2d62981dcfe.png

2026-04-06 01:20:24 UTC

RE: https://mastodon.mit.edu/@jefftk/116347588152920252
#shareGoodNewsToo
#note19ay…8g50

2026-03-30 15:05:27 UTC

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I love the piece, but that die on the right side of the page is really bothering me. On dice, ⚀ and ⚅ are always on opposite sides, with only the very rarest exceptions.
https://media.mathstodon.xyz/media_attachments/files/116/318/734/558/871/093/original/64f6e4e7e50b40ac.jpg
https://media.mathstodon.xyz/media_attachments/files/116/318/734/569/360/017/original/3eabe2f7909502ca.jpg

2026-03-24 10:52:31 UTC

It's 1986. You've built a limited but working time machine. Every week, it materializes a small slip of paper with a news headline from 2026.
You arrange a meeting with a millionaire who might be able to help you exploit your source of future information. She looks skeptical, but you ask her to be patient while you warm up the machine. Presently, a bit of paper materializes from nowhere. The millionaire is impressed.
You hand her the slip, wondering what wisdom it will impart. The outcome of a major sporting event? An election result? The name of a successful company that doesn't yet exist?
But the millionaire's expression changes to a scowl. She lets the slip flutter to the floor as she leaves your apartment without another word.
You retrieve the slip and read the headline that your machine has produced.
https://www.nytimes.com/athletic/7142152/2026/03/23/cornhole-player-amputee-arrested-murder-dayton-webber/

2026-03-13 23:12:50 UTC

A woman sues her insurance company for terminating her disability benefits. They reach a settlement and agree that the suit will be dismissed with prejudice.
She decides she doesn't like the settlement and asks her lawyers to reopen the case.They say they can't: it was dismissed, and in the settlement she agreed not to reopen the case.
She asks ChatGPT if her attorneys are lying to her. It says they are. She fires them and continues pro se, advised by ChatGPT.
CharGPT generates legal arguments for reopening the case, which she files, and 21 more motions, a subpoena, and eight other notices and statements, which she files.
The court denies her motion to reopen the case.
Advised by ChatGPT, she files a new suit against the insurance company and submits 44 more motions, memoranda, etc., which include citations to nonexistent cases.
Now the insurance company has sued OpenAI for tortious interference with their settlement contract.
🍿
https://storage.courtlistener.com/recap/gov.uscourts.ilnd.496515/gov.uscourts.ilnd.496515.1.0_1.pdf

2026-03-10 13:47:25 UTC

My under-desk floor mat
#tilingTuesday
https://media.mathstodon.xyz/media_attachments/files/116/205/187/162/795/002/original/298af73d946aa843.jpg

2026-03-01 10:34:16 UTC

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You are right! But until you said it, I didn't know.

2026-02-24 16:41:16 UTC

#textureTuesday
https://media.mathstodon.xyz/media_attachments/files/116/126/598/295/725/507/original/24f44c0d039dfbda.jpg

2026-02-23 13:40:58 UTC

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At last I understand why so many CT scanners are equipped with snooker tables!

2026-02-21 18:29:14 UTC

“Most electronic shopping cart wheels listen for a 7.8 kHz signal from an underground wire to know when to lock and unlock. A management remote can send a different signal at 7.8 kHz to the wheel to unlock it. Since 7.8 kHz is in the audio range, you can use the parasitic EMF from your phone's speaker to ‘transmit’ a similar code by playing a crafted audio file.”
This sounds improbable but I needed to use it just now and it worked both times.
https://www.begaydocrime.com/

2026-02-20 08:10:49 UTC

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I keep thinking about that incredibly creepy story you wrote about the kidnapping.

2026-02-11 16:59:42 UTC

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This use of “gore” is from an older word “gar” meaning a spear. It's the origin of several common words:
* When the bull gores someone with his horns, it's because he's spearing them
* The gar fish is so-called because it's spear-shaped (See figure 1)
* The garlic plant is a gar-leek because it's like a leek, but with long pointy leaves like a spear (this sounds like something I would make up, but it isn't)
https://media.mathstodon.xyz/media_attachments/files/116/053/057/605/517/762/original/abd77bc198298586.png

2026-02-11 16:51:10 UTC

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Check out "theoretical gore" in this illustration. (Upper right.) "Gore" is actually a rather old word for a triangular-shaped piece of land. (Also a for triangular-shaped piece of fabric in a garment, and more generally for anything spear-shaped.)
In highway design, the “theoretical gore” is the triangular part of the road between the main way and the exit way, the part with white strips that you're not supposed to drive on.
The “physical gore” is the sort of armpit place _off_ the road that you will crash into if you keep driving on the theoretical gore.
I ❤️ #jargon
https://media.mathstodon.xyz/media_attachments/files/116/053/019/984/505/538/original/47e19d993881f0fc.png

2026-02-11 16:42:52 UTC

I was skimming through the Manual on Uniform Traffic Control Devices yesterday, and thinking, as I often do, that one of the finest things in the U.S. is our highway signage. No joke, I am really proud of our achievements here. They are a triumph of civic administration and a valuable application of our affluence for the public good.
(The manual is available online for free and will be of great delight to many varieties of nerd: https://mutcd.fhwa.dot.gov/kno_11th_Edition.htm )
And then I thought it's probably only a matter of time until the current administration figures out a way to line their pockets with highway sign funds, announces that highway signs are Fake News and Woke and fucks them up somehow or eliminates them entirely.
https://media.mathstodon.xyz/media_attachments/files/116/052/990/000/172/406/original/75921a9bac21279c.png

2026-02-08 18:19:25 UTC

Did you know? If you want to _mention_ a hashtag like #lichenSubscribe, but you don't want followers of that hashtag to be alerted to your post (because it isn't actually about lichen) you can set the post's “visibility” to “quiet public”?
It will still be visible to everyone, including your own followers as usual, it just won't alert strangers who are following the hashtag and it won't show up in searches for that hashtag.
https://media.mathstodon.xyz/media_attachments/files/116/036/379/238/034/773/original/33d05c18c70524fe.png

2026-02-02 16:27:21 UTC

RE: https://mathstodon.xyz/@mjd/115968091585502218
@npub1ftl…3e6s
Nobody had an answer to this.
#note1end…tdc7

2026-01-30 19:58:52 UTC

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I figured it out: it was https://www.rfc-editor.org/rfc/rfc9839.html

2026-01-30 14:28:35 UTC

@npub1qw6…xm8d I'm sure I recently read a good blog post with a simply formula for the three kinds of Unicode characters that should be filtered from user input, but I don't know who wrote it or where it was. Does your link log have anything like that?
It's for this person:
https://lethargic.talkative.fish/@suricrasia/statuses/01KG6HET8WZNMWECWFYNC9MTQS

2026-01-29 16:57:31 UTC

How this morning is going: “Why the hell isn't my mouse working?… Oh.”
https://media.mathstodon.xyz/media_attachments/files/115/979/438/448/187/096/original/5c8fd4fb332a43f4.jpg

2026-01-27 16:50:47 UTC

I am looking on the Internet Archive for a downloadable copy of Kierkegaard's _Fear and Trembling_. I don't see any way to restrict the search to items that are downloadable. Instead I have to click on each one in turn, only to find that it is a read-online with a one-hour borrow time, or that it is available only to visually impaired readers, or whatever.
What am I missing?
https://archive.org/search?tab=texts&query=%22fear+and+trembling%22&and%5B%5D=collection%3A%22internetarchivebooks%22

2026-01-26 03:16:13 UTC

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Current frittata:
https://media.mathstodon.xyz/media_attachments/files/115/959/225/350/708/748/original/e285be07f9479573.jpg

2026-01-12 19:01:11 UTC

This is obvious in hindsight, but making a Sunday night frittata is a good way to use up the week's leftovers.
https://media.mathstodon.xyz/media_attachments/files/115/883/662/725/091/599/original/02b5795fb33f5e54.jpg
https://media.mathstodon.xyz/media_attachments/files/115/883/662/724/776/209/original/15e29ef6418c548c.jpg
https://media.mathstodon.xyz/media_attachments/files/115/883/662/725/091/600/original/fa4567c6b62ecb19.jpg
https://media.mathstodon.xyz/media_attachments/files/115/883/668/113/928/129/original/4c73c8fbfbdc58eb.jpg

2026-01-09 14:00:28 UTC

One of the cooler things I saw in the Corning Museum of Glass was this chandelier made of blue glass butterflies. The butterflies are actually made of recycled solar cell material, and they're wired up so that the chandelier lights up with no external power source, the power is supplied by the butterflies themselves.
https://glasscollection.cmog.org/objects/58287/virtue-of-blue
#CMoG
https://media.mathstodon.xyz/media_attachments/files/115/865/480/974/023/923/original/c0d24346155aba83.png
https://media.mathstodon.xyz/media_attachments/files/115/865/481/372/384/510/original/09fd983f5b25fc99.png
https://media.mathstodon.xyz/media_attachments/files/115/865/481/846/191/900/original/37e6e34e7fa47bc0.png

2026-01-02 19:45:37 UTC

I did Google search just now for Padraic Bartlett's excellent lecture notes on spectral graph theory, and discovered that most of the top hits were for my web site, where I had archived them after last time I went looking for them, apparently in 2011. Perhaps foreseeing exactly this moment.
Spectral graph theory is wild. It treats graph adjacency matrices as actual _matrices_ and asks what you can learn about the graph from studying the eigenvalues of the matrix and such like.
If someone had asked me about this before I knew the answer, I would have guessed that there was pretty much nothing you could extract from the eigenvalues of the adjacency matrix. But the opposite is true.
https://www.plover.com/misc/math/Spectral%20Graph%20Theory/

2026-01-02 07:03:40 UTC

For 2026 I have resolved to cease my wasteful use of double leters.
Hapy new year!

2025-12-28 18:38:11 UTC

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https://media.mathstodon.xyz/media_attachments/files/115/798/643/889/167/468/original/33d46750a12717ec.jpg
https://media.mathstodon.xyz/media_attachments/files/115/798/643/904/033/603/original/a5f36ff515f09b00.jpg
https://media.mathstodon.xyz/media_attachments/files/115/798/643/893/735/101/original/8468bb4b0310dfb8.jpg

2025-12-28 18:37:44 UTC

There are six possible axial orientations of an almond in a nutcracker and to my mind one of them is clearly superior to the others.
(Inspired because yesterday I met a grown man who did not know how to crack an almond.)
https://media.mathstodon.xyz/media_attachments/files/115/798/642/328/774/545/original/e059158be6ee1913.jpg
https://media.mathstodon.xyz/media_attachments/files/115/798/642/332/314/674/original/fe236769753d14cb.jpg
https://media.mathstodon.xyz/media_attachments/files/115/798/642/334/746/841/original/78d7cf9bfa73d215.jpg

2025-12-28 15:33:13 UTC

Lately I've been puzzling about the confusingly abstract English word “condition”, trying to think how I would explain it to an English language learning person.
1. I will go with you, on one condition:…
2. What condition is your car in?
3. Air conditioner
4. Conditional statements
5. ??
I haven't found a challenge this hard since “even”.

2025-12-20 13:06:06 UTC

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I once read a story about the people writing the software for the NASA Apollo missions. There was a functionary in charge of weight accounting, who came to them and asked how much the software would weigh.
They told him it weighted nothing, but the functionary had heard *that* one before and insisted—everything had to be accounted down to the last ounce. He demanded to see it.
They showed him a stack of punched cards, and he was triumphant. “You see,” he said smugly, “it doesn't weigh only ‘nothing’!”
“No, you misunderstand,” they replied. “The cards aren't going on the spacecraft. Only the holes.”

2025-12-15 22:53:16 UTC

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https://media.mathstodon.xyz/media_attachments/files/115/726/035/218/061/557/original/d89abcaa36612df4.png
https://media.mathstodon.xyz/media_attachments/files/115/726/036/894/109/785/original/b8ac30941e9f035a.jpg

2025-12-15 22:49:02 UTC

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“The other thing is something that's been bugging me for years, which is programmers …”
(Long pause)
“You know, let's just stop the talk right there.”
https://youtube.com/watch?v=-HlGQtAuZuY#

2025-12-15 22:43:32 UTC

I'm sitting on the sofa watching a recording of a talk I gave in 2014 and I realize that in the video I'm wearing the same sweater I have on right now.

2025-12-14 17:23:41 UTC

RE: https://fandom.ink/@Rozzychan/115714715047589920
#shareGoodNewsToo
#note1rk8…89nt

2025-11-24 09:09:49 UTC

Today I learned about phytoliths.
https://en.wikipedia.org/wiki/Phytolith
(White scale bars in the pictures are 20μm)
https://media.mathstodon.xyz/media_attachments/files/115/603/886/877/996/764/original/438465f7801bed27.png
https://media.mathstodon.xyz/media_attachments/files/115/603/886/877/146/959/original/7140c3b0665e36dc.png

2025-11-15 21:57:17 UTC

About thirty years ago I did a project to enumerate all the quilt blocks of a certain type.
Designs must be made of sixteen of these square components with two opposite-color triangles. They must have fourfold rotational symmetry. Two designs are considered the same if they are reflections of one another, or obtained by exchanging black and white.
There are 72 such designs. I made a mistake and rendered one twice. Can you find it?
https://media.mathstodon.xyz/media_attachments/files/115/555/947/227/903/309/original/c7d59f099f11fd74.jpg

2025-11-10 18:03:24 UTC

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I apparently had a lot of fun with this.
https://media.mathstodon.xyz/media_attachments/files/115/526/715/734/338/954/original/e51440b1304efb03.jpg
https://media.mathstodon.xyz/media_attachments/files/115/526/715/744/905/071/original/3a82614f438a84e0.jpg
https://media.mathstodon.xyz/media_attachments/files/115/526/715/748/538/857/original/5fdbdf6ef7153a1a.jpg
https://media.mathstodon.xyz/media_attachments/files/115/526/715/749/095/002/original/a7a057e26eb017b8.jpg

2025-11-10 17:58:48 UTC

I haven't looked at the Higher-Order Perl errata pages for years, so I had forgotten this detail. All the other pages on the site have a picture of the book cover. But each errata page has instead a random selection from a set of 17 erroneous covers. Some examples:
https://media.mathstodon.xyz/media_attachments/files/115/526/694/930/724/578/original/234d8d6179c094bc.jpg
https://media.mathstodon.xyz/media_attachments/files/115/526/694/955/026/502/original/15139d7daaa763e7.jpg
https://media.mathstodon.xyz/media_attachments/files/115/526/694/971/460/191/original/6c3f8af9d84107a8.jpg
https://media.mathstodon.xyz/media_attachments/files/115/526/694/980/384/037/original/4d20f1541677e580.jpg

2025-11-08 00:42:13 UTC

Today's the fifth anniversary of the infamous Four Seasons Total Lanscaping press conference! Best wishes to all who celebrate!
https://media.mathstodon.xyz/media_attachments/files/115/511/297/710/775/963/original/04adb677af252f35.jpg

2025-11-07 16:34:49 UTC

@npub1rrg…p8jc At the Philadelphia Museum of Art annual craft show
https://media.mathstodon.xyz/media_attachments/files/115/509/380/174/962/189/original/6a76fa01eb6ccf1d.jpg

2025-10-28 08:56:04 UTC

U.S. food assistance benefits won't go out timely in November. Working single moms won't be able to buy food for their little kids or formula for their babies. Housebound old and sick people who need meals delivered won't eat. Good people are going to die.
Please donate CASH to your local food bank. The food bank is a very efficient use of your charity money. $0.75 turns into at least one full meal delivered to someone who needs it, maybe more.
Definitely don't buy canned goods to donate. Just give the food bank the money instead. You'll be feeding five times as many people.
A web search for “New Orleans food bank” or whatever will get you to a page where you can donate.

2025-10-25 15:11:50 UTC

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https://media.mathstodon.xyz/media_attachments/files/115/435/444/723/931/840/original/ac01fd3635e7c412.jpg

2025-10-23 13:33:15 UTC

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It failed right out of the gate there. I'd quote more, but it's more of the dismal same.
https://media.mathstodon.xyz/media_attachments/files/115/423/729/599/525/872/original/b447f1c5b088eed4.png

2025-10-22 15:02:30 UTC

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This very similar example came through my timeline yesterday.
https://mathstodon.xyz/@npub1s7t…xfa0/115414829655492335

2025-10-20 14:49:36 UTC

@npub1c5y…cvcq This is a really cool picture.
https://media.mathstodon.xyz/media_attachments/files/115/407/046/003/036/135/original/a7b9a72f761aedcc.png

2025-10-19 15:08:10 UTC

Seaforest Bakeshop is a new Korean-inspired bakery in Philadelphia. Here is their wrapping paper. (I met the baker today. She looks JUST LIKE the cartoon version of her.)
They're at 16th and Bainbridge. I recommend a visit.
https://media.mathstodon.xyz/media_attachments/files/115/401/454/229/352/537/original/af7d0ce4f376f151.jpg

2025-10-18 19:34:43 UTC

Who's this on the gates of the Greek Orthodox Cathedral of St. George in Philadelphia?
https://media.mathstodon.xyz/media_attachments/files/115/396/840/756/839/180/original/1d4ac737321a3922.jpg

2025-10-14 19:28:36 UTC

Why does Skyrim look to me like a full-scale world, a real place, and the world of The Outer Worlds seems small and fake, like a dollhouse? (Skyrim screenshots are the ones with the stone towers.)
https://media.mathstodon.xyz/media_attachments/files/115/374/164/220/747/383/original/810d7a26e4c9dde7.jpg
https://media.mathstodon.xyz/media_attachments/files/115/374/164/226/240/750/original/c5ff96d991055cc6.jpg
https://media.mathstodon.xyz/media_attachments/files/115/374/164/225/427/572/original/5641c061061d8af4.png
https://media.mathstodon.xyz/media_attachments/files/115/374/164/225/350/807/original/ba559a19df776660.jpg

2025-10-14 11:22:49 UTC

“Eastern Australian humpback whale population now well above pre-whaling levels, report finds”
https://www.abc.net.au/news/science/2025-10-07/humpback-whales-eastern-population-numbers-rebound-estimate/105843256
#shareGoodNewsToo

2025-10-14 09:02:57 UTC

Top comment “That’s an icosahedron you uncultured swine”
Second place: “A NEW HAND TOUCHES THE BEACON”
https://www.reddit.com/r/BrandNewSentence/comments/1o5tc5i/the_guy_next_to_us_on_this_flight_straight_up/
https://media.mathstodon.xyz/media_attachments/files/115/371/702/620/477/743/original/12751ac1dcecf16f.jpeg

2025-10-11 19:42:57 UTC

Thinking about how to count these rectangle-ominoes. There's one of size 1, three of size 2, and rather a lot of size 3. When two tiles touch, they must have at least one vertex and part of the edge in common.
https://media.mathstodon.xyz/media_attachments/files/115/357/236/272/852/527/original/144afef91ba0f08f.jpg
https://media.mathstodon.xyz/media_attachments/files/115/357/238/360/158/030/original/6a689caaefb02b67.jpg
https://media.mathstodon.xyz/media_attachments/files/115/357/238/380/400/406/original/4bf4737bc8665c25.jpg
https://media.mathstodon.xyz/media_attachments/files/115/357/238/380/288/391/original/64803cb4bf0f6219.jpg

2025-10-09 02:05:34 UTC

Happy #worldOctopusDay everyone! (It's the 8th of October.)
Since 2010 or so Lorrie has been making these little felt octopuses. She's made about 3,000 of them and despite having sold and given away many there are still quite a few in our house, lurking about. Here's the most recent batch, fresh from the Felting Spa.
https://media.mathstodon.xyz/media_attachments/files/115/341/755/641/172/050/original/8a7f2e0e04c05350.png

2025-10-08 16:28:58 UTC

Fun 1904 Cyrillic alphabet book for kids, by AlexandreNikolayevich Benois (Алекса́ндр Никола́евич Бенуа́). Depicted below the pages for ц (“ts” for "tsaritsa" (царица), "queen") and ч ("ch" for "chuchelo" (чучело), "dummy").
https://archive.org/details/gri_33125014180802/page/n29/mode/2up
Content warning: letter "А" is an unusually racist caricature of an "Arab".
https://media.mathstodon.xyz/media_attachments/files/115/339/476/302/277/127/original/868a22f7a9204fa4.png

2025-10-06 18:50:55 UTC

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I would be surprised if it were that simple. Consider this problem with the same flavor: four houses lie at the vertices of a one-mile square in a woods. We would like to construct a road network that provides a route from each house to the others, using the smallest possible amount of road.
If we build roads on three sides of the square, that's 3 miles of roads.
If we build an X with the crossroads at the center, that's better, around 2.8284 miles.
But the optimal network uses only 2.732 miles of road, as in the diagram.
See https://en.wikipedia.org/wiki/Steiner_tree_problem
https://media.mathstodon.xyz/media_attachments/files/115/328/718/800/649/576/original/00ca0159c3ddb7ee.png

2025-10-06 00:50:15 UTC

Székelykáposzta
https://media.mathstodon.xyz/media_attachments/files/115/324/471/747/873/040/original/db0a5880e9d56111.jpg

2025-09-26 14:49:42 UTC

I have to assume that this band (2nd from right) is named for Harry Mathews' novel “Tlooth”. It can't be a coincidence, right?
@npub1l83…3zmk
https://media.mathstodon.xyz/media_attachments/files/115/271/145/303/345/305/original/e9676e56e9ecee50.jpg

2025-09-23 14:41:40 UTC

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“Academia.edu is proud to announce that, as part of our company's commitment to DEI, starting from Q1 2026 we will begin accepting first-born daughters as well as sons.”

2025-09-18 22:00:19 UTC

Okay, what if we took Peanuts comics and redrew them so that instead of a dog, Snoopy was a kid in a gimp suit?
He'd still live in Charlie Brown's backyard and eat from a dog bowl, of course.
https://media.mathstodon.xyz/media_attachments/files/115/227/545/629/571/931/original/a083f9320db19534.jpg

2025-09-18 20:50:54 UTC

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I think there's no 'b' until "billion".

2025-09-14 02:52:12 UTC

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I don't know why I thought it was called that, some metaphor maybe, or some Lao word that happened to sound sort of like English “jars”.
Nope. Literal jars.
https://media.mathstodon.xyz/media_attachments/files/115/200/381/987/446/265/original/d239b66d6676e7f7.png

2025-09-13 22:30:37 UTC

Today I learned that the Plain of Jars is so-called because it is covered with actual jars, large stone jars.

2025-09-13 15:11:02 UTC

#itsAlwaysPokeweed
https://media.mathstodon.xyz/media_attachments/files/115/197/624/486/352/373/original/b5f1c45e1038b1f8.jpg

2025-09-13 14:40:26 UTC

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Have you seen this? https://www.thenation.com/article/politics/charlie-kirk-assassination-maga/
“Joseph Goebbels was a gifted marketer and loving father to six children.”

2025-09-08 12:09:03 UTC

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I once read somewhere that if you are having dinner with strangers and you want to know if any of them is a computer programmer, you can ask if anyone there has an opinion on time zones. Normal people will shrug. Programmers will scowl and start to bang their fists on the table.

2025-09-08 11:57:26 UTC

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The fundamental problem with all date-time libraries is this: there are two kinds of objects we need to model.
One is actual times, which (ignoring relativistic effects) are the same everywhere. If I call my mother-in-law in Seoul, the conversation happens at the time time for her as it does for me, regardless of what those times might be _called_.
The other kind of object is _labels_ for times or _descriptions_ for times. If I call Seoul at Mon Sep 8 03:31:11 AM EDT 2025 US/Eastern, that time is also _called_ Mon Sep 8 16:31:11 AM EDT 2025 Asia/Seoul. Two different labels for the same thing.
But every date-time library I've ever used has conflated or confused these two concepts.

2025-09-08 01:15:35 UTC

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I was going to go into detail about where the *fundamental* problem is, not just in Python but in Perl and every other date-time library I've ever used, but after I thought about it for a few minutes I remember I wrote it up already, like ten years ago. But it never changes.

2025-09-08 01:04:08 UTC

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I know where the problem is, too, but I just don't want to get into it with the Freezegun people because suspect that the answer will be that the design of datetime left them with two almost equally unpalatable choices.
Also because to talk about it further, I would have to think about time zones.

2025-09-08 00:58:13 UTC

Fucking time zones, how do they work? (1/2)
```
from datetime import datetime
from freezegun import freeze_time
fake_time = datetime.fromtimestamp(999999)
with freeze_time(fake_time):
assert datetime.now().timestamp() == 999999
```

2025-09-07 15:03:55 UTC

Suppose each of a polyhedron's faces is a non-convex polygon. What's the smallest number of faces it can have?
https://math.stackexchange.com/q/5094422/25554
https://media.mathstodon.xyz/media_attachments/files/115/163/619/033/939/462/original/7bc4a4bfe61e07a4.png

2025-09-07 03:05:04 UTC

@npub1xe9…d8ze Hey, I installed Fira Code on my linux laptop and it looks great in VS Code. But when I tried to select it in GNOME Terminal, it looked like this. Do you know what might be wrong?
https://media.mathstodon.xyz/media_attachments/files/115/160/794/503/330/513/original/8cb2822e1b47e161.png

2025-09-06 20:58:11 UTC

#itsAlwaysPokeweed
https://media.mathstodon.xyz/media_attachments/files/115/159/353/224/578/096/original/8458271234195dec.jpg

2025-09-06 17:49:40 UTC

Pharmacies in Pennsylvania immediately resume COVID-19 vaccines after State Board of Pharmacy votes unanimously to allow pharmacies to rely on guidance from some medical professional societies rather than the CDC.
We're getting our shots later this afternoon.
#shareGoodNewsToo
https://penncapital-star.com/government-politics/pa-board-of-pharmacy-votes-to-use-vaccine-guidelines-from-non-government-groups/

2025-09-05 16:30:04 UTC

Its POKEWEED SEASON!
#itsAlwaysPOKEWEED
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2025-08-30 14:13:35 UTC

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I realised a couple of weeks ago that I had a belief that when these horse chestnut burrs matured they looked like this:
Which makes absolutely no sense, and is false. These are sweetgum burrs.
I think I might have conceived this theory as a small child and then retained it into middle age.
https://media.mathstodon.xyz/media_attachments/files/115/118/124/824/068/863/original/97d826b885a5b481.jpg

2025-08-30 14:06:37 UTC

Autumn, right on schedule, maybe even a couple weeks early for a change.
https://media.mathstodon.xyz/media_attachments/files/115/118/094/887/756/387/original/0437b78a1c894aa6.jpg

2025-08-29 04:34:57 UTC

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2025-08-29 04:34:37 UTC

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2025-08-26 19:29:37 UTC

I think many people misunderstand the purpose of code review. The purpose of code review is not for the reviewer to find bugs, and certainly not for them to ensure that the code is bug-free. Anyone who depends on code review to find bugs is living in a fool's paradise. As everyone should know by now, it is not in general possible to find bugs by examining the code.
The primary purpose of code review is to find code that will be _hard to maintain_. The reviewer looks at the code and tries to understand what it is doing and how. If they can't, that means it will be hard to maintain in the future, and should be fixed now, while the original author is still familiar with it.

2025-08-26 14:41:45 UTC

I've been writing automated tests for decades now. And I still find myself saying things like “oh, this is trivial, I don't need to write a test for it” or “oh, this is just a wrapper around X, and the tests for X pass, I don't need to write a test for it” and then I write the tests anyway and they fail because my trivial wrapper had a bug.
Most recently: A web app where an HTTP endpoint, `delete-player-data` looks up the player's record and passes it to a `delete_related_records` function that deletes some records. The `delete_related_records` function is well-tested and works properly when passed a player record. The tests for the HTTP endpoint will be almost the same: set up the same fixture data, and do the same checks that the data is really gone after the request is sent to the endpoint. Do I really have to do this?
Friends, the endpoint was wrong and its tests failed. I had forgotten to have the endpoint commit the transaction after calling `delete_related_records` before returning, so the changes were rolled back.
I have trained myself pretty well that when I have these thoughts—which is pretty often—another part of my brain yells
JUST WRITE THE TESTS, FOOL.

2025-08-24 14:03:53 UTC

Aha! Wish I'd thought of this before, it's the exact same idea but in a simpler version. It's the usual definition for an exponential object $ Z^Y$ in a category, except instead of considering arrows $ g': X\to Z^Y $ in general, we consider only the case $ X=1 $.
Easier to get my head around as a halfway step toward the full definition.
#categoryTheory
https://media.mathstodon.xyz/media_attachments/files/115/084/113/678/621/659/original/b95231ad48b48506.jpg

2025-08-21 21:21:42 UTC

Enjoy this artwork of _Hallucigenia_ being fitted for new socks. Last time, the sock lady tried to put the socks onto its dorsal spines. So embarrassing!
https://en.wikipedia.org/wiki/Hallucigenia
Original source:
https://www.pixiv.net/en/artworks/19114605
https://media.mathstodon.xyz/media_attachments/files/115/068/838/050/218/631/original/8fa3297efc0fee96.png

2025-08-21 21:07:54 UTC

NO RETROMINGENCY
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2025-08-21 20:52:25 UTC

@npub1ye2…wm6h I found this small tile mosaic out back of Christianne's Lyceum in Vancouver.
https://media.mathstodon.xyz/media_attachments/files/115/068/731/140/396/215/original/906450a69110654b.jpg

2025-08-19 18:09:10 UTC

#TilingTuesday
https://media.mathstodon.xyz/media_attachments/files/115/056/767/450/617/982/original/6eeec2f28526a52c.jpg

2025-08-19 16:48:39 UTC

#TilingTuesday
Two different kinds of dodecagons.
(One set is only kinda sorta dodecagons, but you can see what I mean.)
https://media.mathstodon.xyz/media_attachments/files/115/056/446/520/026/954/original/8e96d71c162ef59e.jpg
https://media.mathstodon.xyz/media_attachments/files/115/056/446/652/054/957/original/9bd4d6679086fa59.jpg

2025-08-19 03:48:31 UTC

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I tried a while back to get Claude to do some simple graph theory and was dismayed at how badly it did. It made many correct statements, but most were nonsequiturs.
https://blog.plover.com/tech/gpt/graph-theory.html
I've had good results from Claude, but not for anything like this. I think it might have worked better to have asked it to write a program to search for the solution.

2025-08-16 21:18:20 UTC

#mosstodon #lichenSubscribe
https://media.mathstodon.xyz/media_attachments/files/115/040/523/199/349/540/original/b0ad1f093f93bda8.jpg

2025-08-16 17:25:12 UTC

“Well, you see, the other two Brits died.”
https://media.mathstodon.xyz/media_attachments/files/115/039/607/885/961/412/original/043775e59f28afeb.jpg