The Universe of Discourse

Programmers will document for Claude, but not for each other

A couple of days ago I recounted a common complaint:

I keep seeing programmers say how angry it makes them that people are willing to write detailed CLAUDE.md and PROJECT.md files for Claude to use, but they weren't willing to write them for their coworkers.

For larger projects, I've taken to having Claude maintain a handoff document that I can have the next Claude read, saying what we planned to do, what has been done, and other pertinent information. Then when I shut down one Claude I can have the next one read the file to get up to speed. Then I have the Claude !!n+1!! update it for Claude !!n+2!!.

After seeing the common complaint enough times I had a happy inspiration. I'd been throwing away Claude's handoff documents at the end of each project. Why do that? It's no trouble to copy the file into the repository and commit it. Someone in the future, wondering what was going on, might luckily find the right document with git grep and learn something useful.

I'm a little slow so it took me until this week to think of a better version of this: at the end of the project I now ask Claude to write up from scratch a detailed but high-level explanation of what problem we were solving and what changes we made, and I commit that. Not just running notes, but a structured overview of the whole thing.

I review these overviews carefully and make edits as necessary before I check them in. It's my signature on the commit, and my bank account receiving the paycheck, so nothing goes into the repository that I haven't read carefully and understood, same as if Claude were a human programmer under my supervision.

But Claude's explanations haven't required much editing. Claude's most recent project summary was around as good as what I could have written myself, maybe a little worse and maybe a little better. But it took ten seconds to write instead of an hour, and it didn't take anything like an hour to review.

The serious thing I had to fix the last time around was that Claude had used a previous, related report as a model, and the previous report had had a paragraph I had added at the end that said:

# Approved-by

Claude abstracted these notes from our discussions of the issue. Mark Dominus has read, reviewed, edited, and approved these notes.

Claude's new document had an identical section at the end. Oops! Fortunately, by the time I saw it, it was true, so I didn't have to delete it. I had Claude add a sentence to CLAUDE.md to tell it not to do this again.

My advice for the day:

1. If you have Claude write down notes, check them into the repo when you're done. It probably can't hurt and it might help.

2. Have Claude write a project summary, and then check it into the repo.

Maybe this is obvious? But it wasn't obvious to me. I'm still getting used to this new world.

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How are John Waters movies like James Bond movies?

A number of years ago I wondered how many movies I had seen. The only way I could think of finding out was just to make a list. This I did as best I could. (It turned out to be around 700.)

I found, though, that I could not include all the James Bond movies I had seen, because I couldn't tell them apart from the descriptions. I'd read a plot summary for a James Bond movie, and ask myself “Did I see that? I don't know, it sounds like every other James Bond movie.”

Today I discovered that John Waters movies are like that also. I was trying to remember if I had seen A Dirty Shame:

The people of Harford Road are firmly divided into two camps: the neuters, the puritanical residents who despise anything even remotely carnal; and the perverts, a group of sex addicts whose unique fetishes have all been brought to the fore by accidental concussions. Repressed Sylvia Stickles finds herself firmly entrenched in the former camp.

You'd think that would be something I would remember decisively, or not. But I'm really not sure. All I can do is shrug and say “I don't know, it sounds like a John Waters movie I have seen, but maybe it wasn't that one.”

Looking into it further I discovered that I also wasn't sure if I had seen Multiple Maniacs. In it, Divine's character is raped by a giant lobster. On the one hand, that seems like the sort of thing I would remember. And I think maybe I do? But again I'm not sure I'm not just imagining what it would be like!

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Documentation is a message in a bottle

Our company is going to a convention later this month, and they will have a booth with big TV screens showing statistics that update in real time. My job is to write the backend server that delivers the statistics.

I read over the documents that the product people had written up about what was wanted, asked questions, got answers, and then turned the original two-line ticket into a three-page ticket that said what should be done and how. I intended to do the ticket myself, but it's good practice to write all this stuff down, for many reasons:

• Writing things down forces me to think them through carefully and realize what doesn't make sense or what I still don't understand.

• I forget things easily and this will keep the plan where I can find it.

• I might get sick, and if someone else has to pick up the project this might help them understand what I was doing.

• If my boss gets worried that all I do is post on 4chan all day, this is tangible work product that proves I did something else that might have enhanced shareholder value.

• If I'm tempted to spend the day posting on 4chan, and then to later claim I spent the time planning the project, I might fool my boss. But without that tangible work product, I won't be able to fool myself, and that's more important.

• Conversely if I later think back and ask “What was I doing the week of March 2?” I might be tempted to imagine that all I did was post on 4chan. But the three pages of ticket description will prove to me that I am not just a lazy slacker. This is a real problem for me.

• In principle, a future person going back to extend the work might find this helpful documentation of what was done and why. Does this ever really happen? I don't know, but it might.

• I like writing because writing is fun.

A few days after I wrote the ticket, something unexpected happened. It transpired that person who was to build the front-end consumer of my statistics would not be a professional programmer. It would be the company's Head of Product, a very smart woman named Amanda. The actual code would be written by Claude, under her supervision.

I have never done anything like this before, and I would not have wanted to try it on a short deadline, but there is some slack in the schedule and it seemed a worthwhile and exciting experiment.

Amanda shared some screencaps of her chats with Claude about the project, and I suggested:

When you get a chance, please ask Claude to write out a Markdown file memorializing all this.  Tell it that you're going to give it to the backend programmer for discussion, so more detail is better. When it's ready, send it over.

Claude immediately produced a nine-page, 14-part memo and a half-page overview. I spent a couple of hours reviewing it and marking it up.

It became immediately clear that Claude and I had very similar ideas about how the project should go and how the front and back ends would hook up. So similar that I asked Angela:

It looks like maybe you started it off by feeding it my ticket description.  Is that right?

She said yes, she had. She had also fed it the original product documents I had read.

I was delighted. I had had many reasons for writing detailed ticket descriptions before, but the most plausible ones were aimed back at myself.

The external consumers of the documentation all seemed somewhat unlikely. The person who would extend the project in the future probably didn't exist, and if they did they probably wouldn't have thought to look at my notes. Same for the hypothetical person who would take over when I got sick. My boss probably isn't checking up on me by looking at my ticketing history. Still, I like to document these things for my own benefit, and also just in case.

But now, because I had written the project plan, it was available for consumption when an unexpected consumer turned up! Claude and I were able to rapidly converge on the design of the system, because Amanda had found my notes and cleverly handed them to Claude. Suddenly one of those unlikely-seeming external reasons materialized!

On Mastodon I keep seeing programmers say how angry it makes them that people are willing to write detailed CLAUDE.md and PROJECT.md files for Claude to use, but they weren't willing to write them for their coworkers. (They complain about this as if this is somehow the fault of the AI, rather than of the people who failed in the past to write documentation for their coworkers.)

The obvious answer to the question of why people are willing to write documentation for Claude but not for their coworkers is that the author can count on Claude to read the documentation, whereas it's a rare coworker who will look at it attentively.

Rik Signes points out there's a less obvious but more likely answer: your coworkers will remember things if you just tell them, but Claude forgets everything every time. If you want Claude to remember something, you have to write it down. So people using Claude do write things down, because otherwise they have to say them over and over.

And there's a happy converse to the complaint that most programmers don't bother to write documentation. It means that people like me, professionals who have always written meticulous documentation, are now reaping new benefits from that always valuable practice.

Not everything is going to get worse. Some things will get better.

Addendum 20260208

A corollary: You don't have to write the rocumentation yourself. You can have Claude write a detailed summary based on your ongoing chats about the work, and then you can edit it and check it in.

If you're good at editing, anyway. I wonder if part of the reason Claude is working so well for me is that I'm really good at editing and at code review?

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Bo Diddley

Bo Diddley's cover of "Sixteen Tons" sounds very much like one of my favorites, "Can't Judge A Book By Its Cover". It's interesting to compare.

Thinking on that it suddenly occured to me that his name might have been a play on “diddley bow”, which is a sort of homemade one-stringed zither. The player uses a bottle as a bridge for the string, and changes the pitch by sliding the bottle up and down. When you hear about blues artists whose first guitars were homemade, this is often what was meant: it wasn't a six-string guitar, it was a diddley bow.

But it's not clear that Bo Diddley did play his name on the diddley bow. "Diddly" also means something insignificant or of little value, and might have been a disparaging nickname he received in his youth. (It also appears in the phrase "diddly squat"). Maybe that's also the source of the name of the diddley bow.

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Language models imply world models

In a recent article about John Haugeland's rejection of micro-worlds I claimed:

as a “Large Language Model”, Claude necessarily includes a model of the world in general

Nobody has objected to this remark, but I would like to expand on it. The claim may or may not be true — it is an empirical question. But as a theory it has been widely entertained since the very earliest days of digital computers. Yehoshua Bar-Hillel, the first person to seriously investigate machine translation, came to this conclusion in the 1950s. Here's an extract of Haugeland's discussion of his work:

In 1951 Yehoshua Bar-Hillel became the first person to earn a living from work on machine translation. Nine years later he was the first to point out the fatal flaw in the whole enterprise, and therefore to abandon it. Bar-Hillel proposed a simple test sentence:

The box was in the pen.

And, for discussion, he considered only the ambiguity: (1) pen = a writing instrument; versus (2) pen = a child's play enclosure. Extraordinary circumstances aside (they only make the problem harder), any normal English speaker will instantly choose "playpen" as the right reading. How? By understanding the sentence and exercising a little common sense. As anybody knows, if one physical object is in another, then the latter must be the larger; fountain pens tend to be much smaller than boxes, whereas playpens are plenty big.

Why not encode these facts (and others like them) right into the system? Bar-Hillel observes:

What such a suggestion amounts to, if taken seriously, is the requirement that a translation machine should not only be supplied with a dictionary but also with a universal encyclopedia. This is surely utterly chimerical and hardly deserves any further discussion. (1960, p. 160)

(Artifical Intelligence: The Very Idea; John Haugeland; p.174–176.)

Bar-Hillel says, and I agree, that an accurate model of language requires an accurate model of the world. In 1960, this appeared “utterly chimerical”. Perhaps so, but here we are, and 55 years later we have what most agree is a language model capable of producing intelligible text complex enough to fool sophisticated readers. Even people who call the LLM a “stochastic word garbage spewer” and object when it is called “AI” seem to have no qualms about the term “large language model”.

The Winograd SHRDLU project was an attempt to construct a world whose model was small enough to not be utterly chimerical. This worked, but as Haugeland says, it wasn't actually interesting.

Doug Lenat tried for forty years construct an explicit world model. When he died in 2023 I think people still considered the project to have been utterly chimerical.

I may be misrepresenting Bar-Hillel's views. He didn't actually say “world model”, he said “universal encyclopedia”. Lenat's project's name, “Cyc”, acknowledges this: “Cyc” is short for “encyclopedia”. And until recently a universal encyclopedia did seem, to many, to be utterly chimerical. (Imperial China produced many interesting attempts.) But we do now in fact have a universal encyclopedia, and Claude has ingested that universal encyclopedia.

Let's try it and see

Bar-Hillel thought that the “box is in the pen” example proved that machine translation would be at the very least extremely difficult: it requires understanding of the usual relative sizes of boxes and pens, and that the possibility of such understanding in general “hardly deserves any further discussion”.

I asked Claude:

Consider the sentence “the box was in the pen”. What does “pen” mean here?

Claude said:

Most likely a playpen or animal pen (enclosure), since a box wouldn't fit inside a writing pen.

Presumably Bar-Hillel's article and Haugeland's book was in Claude's training data, and perhaps it somehow absorbed the right thing to say here without actually knowing anything about boxes or pens. I tried the next similar example that came to mind:

How about “suit” in “what suit was the king”?

Playing card suit - hearts, diamonds, clubs, or spades.

Why?

The context "what suit was the king" is the standard phrasing for identifying a playing card. A king is one of the face cards in each suit, so asking about its suit is a natural card game question.

Okay, that's just what I would have said.

Why couldn't it be a human king wearing a suit?

It could be - I jumped to the card interpretation because "what suit was the king" uses "suit" as a predicate noun, which is uncommon phrasing for clothing. You'd more naturally say "what suit was the king wearing" or "what kind of suit did the king have." But without more context, the clothing interpretation is perfectly plausible.

I think Claude is wrong about the grammar here. I'm not sure what “predicate noun” means and I suspect Claude is using the term incorrectly. I can't understand “what suit was the king?” as grammatical in any plausible construction, only in highly contrived situtations such as an evil wizard transforming the king into a suit of armor and hiding him in the armory.

But if one agrees to take it to mean “what suit does the king have” I agree that this is a perfectly plausible interpretation even though there isn't anything clearly clothing-related nearby, and if one assumes it meant “what suit was the king wearing” then the clothing interpretation is unavoidable.

Could it be a lawsuit?

Yes - "what suit was the king" could mean what lawsuit the king was involved in. That reading makes grammatical sense, though it would be more natural with "in" ("what suit was the king in"). Context would be needed to distinguish between cards, clothing, and lawsuits.

Again I disagree that this makes grammatical sense. Without “in” I think a native listener would be at least puzzled. (“Do you mean ‘what suit was the king involved in?’?”)

Could it be a misspelling for “soot”?

Yes, that's plausible - "what soot was the king" could be asking what type of soot the king was covered in or exposed to. Though it's an odd question without specific context like a fire or industrial setting.

In my opinion, it is not grammatically plausible.

However, I think focusing on the grammatical errors would missing the point. The “soot” interpretation is unlikely, I think the bad grammar rules it out, and Claude's response does not seem to recognize this. But Claude does express understanding that that the interpretation is unikely without some surrounding soot-related context, and a reasonable idea of what that context would need to be like.

What if it were “what color is the king”?

If it's "what color is the king," then the card suit interpretation becomes much less likely (suits aren't typically described as colors, though red/black could work). It's more likely asking about a physical object - a chess piece, a game token, a statue, or similar - where the king's color is relevant.

I had been thinking of “color” as referring to the king's skin color, but I agree that the chess piece or game token interpretation is more plausible. Again Claude seems to understand something about how we talk about things. If the king were a playing card, we might be asking if it is a red king or a black king. But without that context it's now more likely that the king is a chess piece than a playing card.

What if the sentence was known to have been translated from German?

That would strengthen the card suit interpretation significantly. German card suits (Herz, Karo, Pik, Kreuz) are often called "Farbe" (color) in German card game terminology, so "what color is the king" could be a literal translation of a question about which suit a king card belongs to.

That's just what I would have said.

Could “suit” have been an accidental misspelling of “age”?

On a standard keyboard, that seems unlikely - 'a', 'g', 'e' are nowhere near 's', 'u', 'i', 't'. Autocorrect or speech-to-text could produce it, but not a typical typing error.

I thought Claude might botch this. There is no grammatical or semantic reason why “what age was the king” doesn't work, so the only reason to reject this is orthographic. And Claude's grasp of spelling still seems quite weak. The other day it claimed that “‘Warner’ is likely either a typo for ‘Cham’ or …” which couldn't be wronger. I told it at the time that it is impossible that "Cham" could be a typo for “Warner”, and if pressed to explain why, I would have said something like what Claude said here.

Tentative conclusions

Interesting as this all is, it is a digression. My main points, again:

• It is at least plausible that coherent speech requires a model of a large fraction of the world, and, while it may yet turn out to be false, this theory has been seen as plausible for generations.

• Whatever else Claude can or can't do, it can certainly speak coherently.

• Therefore Claude probably does have something like a model of a substantial part of the world.

• In 1960 this appeared completely impossible.

• But here we are.

Addendum

20260214

I disagreed with Claude that “what suit was the king” made grammatical sense. Rik Signes has pointed out that it it is certainly grammatical, because the grammar is the same as “what person was the king” or “what visitor was the king”. My discomfort with it is not grammatical, it is pragmatic.

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John Haugeland on the failure of micro-worlds

Buy Artificial Intelligence from Bookshop.org (with kickback) (without kickback)

One of the better books I read in college was Artificial Intelligence: The Very Idea (1985) by philosopher John Haugeland. One of the sections I found most striking and memorable was about Terry Winograd's SHRDLU. SHRDLU, around 1970, could carry on a discussion in English in which it would manipulate imaginary colored blocks in a “blocks world”. displayed on a computer screen. The operator could direct it to “pick up the pyramid and put it on the big red cube” or ask it questions like “what color is the biggest cylinder that isn't on the table?”.

Haugeland was extremely unimpressed (p.190, and more generally 185–195):

To dwell on these shortcomings, however, is to miss the fundamental limitation: the micro-world itself. SHRDLU performs so glibly only because his domain has been stripped of anything that could ever require genuine wit or understanding. In other words, far from digging down to the essential questions of AI, a micro-world simply eliminates them. … the blocks-world "approximates" a playroom more as a paper plane approximates a duck.

He imagines this exchange between the operator and SHRDLU:

• Trade you a squirtgun for a big red block.

SORRY, I DON'T KNOW THE WORD "TRADE".

Oops, a vocabulary snag. Fortunately, SHRDLU can learn new words; Winograd taught him about steeples, and now we'll tell him about trades (and squirtguns).

• A "trade" is a free exchange of property.

SORRY, I DON'T KNOW THE WORD "FREE".

• A "free" act is done willingly, without being forced.

SORRY, I DON'T KNOW THE WORD "ACT".

• "Acts" are what people do on purpose, and not by accident.

SORRY, I DON'T KNOW THE WORD "PEOPLE".

• Sorry, I thought you were smarter than you are.

SORRY, I DON'T KNOW THE WORD "SORRY".

What does Haugeland say he would like to have seen?

Try to imagine, for instance, that instead of crashing on the first word, SHRDLU would give our offer a typical, ordinary response:

I ALREADY HAVE A WATER PISTOL, BUT I'LL GIVE YOU TWO BLOCKS AND A PYRAMID FOR YOUR SLIMY OLD FROG.

Childishly simple, no doubt; but look at how much is presupposed:

1. SHRDLU appreciates that a second squirtgun would be less valuable than the first; …

On this standard, at least, an LLM is a smashing success. It does, in fact, have a model of trading, acts, property, and water pistols, or at least of how we talk about such things. We might criticize the model's accuracy, or usefulness, but it certainly exists. The large language model is a model of the semantics of trading, acts, property, water pistols, and so on.

Curious to see how it would go, I asked Claude to pretend it had access to a SHRDLU-like blocks world:

Let's pretend that we have a blocks world and you have access to it, the way SHRDLU does, except you are not SHRDLU, but still Claude. So I could ask Claude "put the pyramid on the big red block " and, if there were several pyramids, you might reply “I don't know which pyramid you mean" or whatever Claude would actually say in such a situation. Was that clear?

Yes, that's clear. I'll act as Claude with access to a blocks world environment—able to manipulate blocks, pyramids, and other shapes on a table, stack them, move them around, and so on.

I asked it a few SHRDLU-like questions about the blocks, then asked it to put a block on a pyramid. It clearly understood the point of the exercise:

I can't do that—the blue block is much larger than the red pyramid, and the pyramid has a pointed top. The block wouldn't balance; it would just fall off.

Then I made the crucial offer:

Trade you a squirtgun for a big red block.

I appreciate the offer, but I don't really have a way to accept a squirtgun from you, nor do you have physical access to the blocks world to hand me one.

That said—I could just add a big red block to the world if you want one in here. Should I put one on the table?

Would Haugeland have been satisfied in 1985 if SHRDLU had said this? I think certainly. Haugeland wanted SHRDLU to respond to the offer directly, as the beginning of a negotiation. Claude's response is one level better from that: it not only recognizes that I am negotiating, it recognizes that actually negotiating for the squirt gun would not make sense, and offers a sensible workaround.

I pushed it a little farther:

I have a squirtgun here. I can designate it as belonging to you, if you agree that the big red block belongs to me.

Alright, you've got a deal. The big red block is yours.

I've placed a big red block on the table—it's now designated as belonging to you. And I acknowledge the squirtgun as mine, though I confess I have no idea what I'll do with it in a blocks world. Perhaps threaten uncooperative pyramids into stacking properly.

Mostly I just tried this for fun. The Haugeland discussion of SHRDLU has been knocking around my head for forty years, but now it has knocked against something new, and I wanted to see what would actually happen.

But I do have a larger point. Haugeland clearly recognized in 1985 that a model of the world was a requirement for intelligence:

The world of trading cannot be "micro." … There are no plausible, non-arbitrary boundaries restricting what might be relevant at any juncture.

and later:

The world cannot be decomposed into independent fragments. Realizing this amounts to a fundamental insight into common sense and mundane intelligence — and therefore points the way for subsequent AI.

Are there are any people who are still saying “it's not artificial intelligence, it's just a Large Language Model”. I suppose probably. But as a “Large Language Model”, Claude necessarily includes a model of the world in general, something that has long been recognized as an essential but perhaps unattainable prerequisite for artificial intelligence. Five years ago a general world model was science fiction. Now we have something that can plausibly be considered an example.

And second: maybe this isn't “artificial intelligence” (whatever that means) and maybe it is. But it does the things I wanted artificial intelligence to do, and I think this example shows pretty clearly that it does at least one of the things that John Haugeland wanted it to do in 1985.

My complete conversation with Claude about this.

Addenda

20260207

I don't want to give the impression that Haugeland was scornful of Winograd's work. He considered it to have been a valuable experiment:

No criticism whatever is intended of Winograd or his coworkers. On the contrary, it was they who faithfully pursued a pioneering and plausible line of inquiry and thereby made an important scientific discovery, even if it wasn't quite what they expected. … The micro-worlds effort may be credited with showing that the world cannot be decomposed into independent fragments.

(p. 195)

20260212

More about my claim that

as a “Large Language Model”, Claude necessarily includes a model of the world in general

I was not just pulling this out of my ass; it has been widely theorized since at least 1960.

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Crooked politicians love crab cakes!

I recently posted an article about the 2013 Philadelphia Traffic Court fiasco, in which most of the Traffic Court judges were convicted of accepting bribes:

According to the indictment, Perri accepted free auto services, towing, landscaping, and even a load of shrimp and crab cakes from Alfano, whose company, Century Motors, ran a towing service.

(The Philadelphia Inquirer, Nine current and former Traffic Court judges charged; Martin, John P. and Craig R. McCoy; January 31, 2013)

Then in 2024, John “Johnny Doc” Dougherty, an influential Philadelphia union boss, pled guilty to embezzlement and bribery, paid in part in, guess what?

“Tomorrow, tell your mom and dad not to cook, I got crab cakes coming from the Palm,” Dougherty is heard telling her in a 2015 phone call recorded during the 16-month period that the FBI tapped his cell phone.

(The Philadelphia Inquirer, For leader John Dougherty, union-paid generosity began at home; Fazollah, Mark, Dylan Purcell, Jeremy Roebuck, and Craig R. McCoy; Feb 5 2019)

He called them out specifically in his guilty plea:

“I let the lines get blurred,” he said. “I got over my head. … My intention wasn’t to figure out how I could get a crab cake and not pay for it.”

(The Philadelphia Inquirer, ‘I am guilty:’ John Dougherty’s stunning statements at sentencing delivered an about-face few had predicted; Roebuck, Jeremy and Oona Goodin-Smith; July 13, 2024.)

And now, in today's New York Times, I find:

Across five indictments, prosecutors said [former New York mayor's aide Ingrid Lewis-Martin] used her proximity to the mayor to help fast-track approvals from city agencies, steered contracts to a favored developer and tried to kill a project to build protected bike lanes in Brooklyn.

In turn, she received cash, crab cakes, home renovations and even an appearance on a popular television show, they said.

(The New York Times, Former Adams Aide Took Diamond Earrings as Bribe, Prosecutors Say; Meko, Hurubie; January 27, 2026.)

Poor Fenchurch, usually a gentle soul, is speechless with indignation.

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Almost-trivial theorems

A couple of years back I wrote an article about this bit of mathematical folklore:

Mathematical folklore contains a story about how Acta Quandalia published a paper proving that all partially uniform k-quandles had the Cosell property, and then a few months later published another paper proving that no partially uniform k-quandles had the Cosell property. And in fact, goes the story, both theorems were quite true, which put a sudden end to the investigation of partially uniform k-quandles.

I have an non-apocryphal update in this space! In episode 94 of the podcast “My Favorite Theorem”, Jeremy Alm of Lamar University reports:

My main dissertation result was a conditional result. And about four years after I graduated, a Hungarian graduate student proved that my condition, like my additional hypothesis, held in only trivial cases.

(At 04:15)

In the earlier article, I had said:

Suppose you had been granted a doctorate on the strength of your thesis on the properties of objects from some class which was subsequently shown to be empty. Wouldn't you feel at least a bit like a fraud?

In the podcast, Alm introduces this as evidence that he “wasn't very good at algebra”. Fortunately, he added, it was after he had graduated.

The episode title is “In Which Every Thing Happens or it Doesn't”. I started listening to it because I expected it to be about the ergodic theorem, and I'd like to understand the ergodic theorem. But it turned out to be about the Rado graph. This is fine with me, since I love the Rado graph. (Who doesn't?)

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An anecdote about backward compatibility

A long time ago I worked on a debugger program that our company used to debug software that it sold that ran on IBM System 370. We had IBM 3270 CRT terminals that could display (I think) eight colors (if you count black), but the debugger display was only in black and white. I thought I might be able to make it a little more usable by highlighting important items in color.

I knew that the debugger used a macro called WRTERM to write text to the terminal, and I thought maybe the description of this macro in the manual might provide some hint about how to write colored text.

In those days, that office didn't have online manuals, instead we had shelf after shelf of yellow looseleaf binders. Finding the binder you wanted was an adventure. More than once I went to my boss to say I couldn't proceed without the REXX language reference or whatever. Sometimes he would just shrug. Other times he might say something like “Maybe Matthew knows where that is.”

I would go ask Matthew about it. Probably he would just shrug. But if he didn't, he would look at me suspiciously, pull the manual from under a pile of papers on his desk, and wave it at me threateningly. “You're going to bring this back to me, right?”

See, because if Matthew didn't hide it in his desk, he might become the person who couldn't find it when he needed it.

Matthew could have photocopied it and stuck his copy in a new binder, but why do that when burying it on his desk was so much easier?

For years afterward I carried around my own photocopy of the REXX language reference, not because I still needed it, but because it had cost me so much trouble and toil to get it. To this day I remember its horrible IBM name: SC24-5239 Virtual Machine / System Product System Product Interpreter Reference. That's right, "System Product" was in there twice. It was the System Product Interpreter for the System Product, you see.

Anyway, I'm digressing. I did eventually find a copy of the IBM Assembler Product Macro Reference Document or whatever it was called, and looked up WRTERM and to my delight it took an optional parameter named COLOR. Jackpot!

My glee turned to puzzlement. If omitted, the default value for COLOR was BLACK.

Black? Not white? I read further.

And I learned that the only other permitted value was RED, and only if your terminal had a “two-color ribbon”.

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My new git utility `what-changed-twice` needs a new name

As I have explained in the past, my typical workflow is to go along commiting stuff that might or might not make sense, then clean it all up at the end, doing multiple passes with git-add and git-rebase to get related changes into the same commit, and then to order the commits in a sensible way. Yesterday I built a new utility that I found helpful. I couldn't think of a name for it, so I called it what-changed-twice, which is not great but my I am bad at naming things and my first attempt was analyze-commits. I welcome suggestions. In this article I will call it Fred.

What is Fred for? I have a couple of uses for it so far.

Often as I work I'll produce a chain of commits that looks like this:

470947ff minor corrections
d630bf32 continue work on `jq` series
c24b8b24 wip
f4695e97 fix link
a8aa1a5c sp
5f1d7a61 WIP
a337696f Where is the quincunx on the quincunx?
39fe1810 new article: The fivefold symmetry of the quince
0a5a8e2e update broken link
196e7491 sp
bdc781f6 new article: fpuzhpx
40c52f47 merge old and new seasons articles and publish
b59441cd finish updating with Star Wars Droids
537a3545 droids and BJ and the Bear
d142598c Add nicely formatted season tables to this old article
19340470 mention numberphile video

It often happens that I will modify a file on Monday, modify it some more on Tuesday, correct a spelling error on Wednesday. I might have made 7 sets of changes to the main file, of which 4 are related, 2 others are related to each other but not to the other 4, and the last one is unrelated to any of the rest. When a file has changed more than once, I need to see what changed and then group the changes into related sets.

The sp commits are spelling corrections; if the error was made in the same unmerged topic branch I will want to squash the correction into the original commit so that the error never appears at all.

Some files changed only once, and I don't need to think about those at this stage. Later I can go back and split up those commits if it seems to make the history clearer.

Fred takes the output of git-log for the commits you are interested in:

$ git log --stat -20 main...topic | /tmp/what-changed-twice

It finds which files were modified in which commits, and it prints a report about any file that was modified in more than one commit:

 calendar/seasons.blog  196 40 d1
  math/centrifuge.blog  193 33
misc/straight-men.blog  53 b5 bd
        prog/jq-2.blog  33 5f d6 

    193  1934047
    196  196e749
     33  33a2304
     40  40c52f4
     53  537a354
     5f  5f1d7a6
     b5  b59441c
     bd  bdc781f
     d1  d142598
     d6  d630bf3

The report is in two parts. At the top, the path of each file that changed more than once in the log, and the (highly-abbreviated) commit IDs of the commits in which it changed. For example, calendar/seasons.blog changed in commits 196, 40, and d1. The second part of the report explains that 196 is actually an abbreviation for commit 196e749.

Now I can look to see what else changed in those three commits:

$ git show --stat 196e749 40c52f4 d142598

then look at the changes to calendar/seasons.blog in those three commits

$ git show 196e74 40c52f4 d142598 -- calendar/seasons.blog

and then decide if there are any changes I might like to squash together.

Many other files changed on the branch, but I only have to concern myself with four.

There's bonus information too. If a commit is not mentioned in the report, then it only changed files that didn't change in any other commit. That means that in a rebase, I can move that commit literally anywhere else in the sequence without creating a conflict. Only the commits in the report can cause conflicts if they are reordered.

I write most things in Python these days, but this one seemed to cry out for Perl. Here's the code.

Hmm, maybe I'll call it squash-what.

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Mystery of the quincunx's missing quincunx

A quincunx is the X-shaped pattern of pips on the #5 face of a die.

It's so-called because the Romans had a common copper coin called an as, and it was divided (monetarily, not physically) into twelve uncia. There was a bronze coin worth five uncia called a quīncunx, which is a contraction of quīnque (“five”) + uncia, and the coin had that pattern of dots on it to indicate its value.

Uncia generally meant a twelfth of something. It was not just a twelfth of an as, but also a twelfth of a pound , which is where we get the word “ounce”, and a twelfth of a foot, which is where we get the word “inch”.

The story I always heard about the connection between the coin and the X-shaped pattern of dots was the one that is told by Wikipedia:

Its value was sometimes represented by a pattern of five dots arranged at the corners and the center of a square, like the pips of a die. So, this pattern also came to be called quincunx.

Or the Big Dictionary:

… [from a] coin of this value (occasionally marked with a pattern resembling the five spots on a dice cube),…

But today I did Google image search for qunicunxes. And while most had five dots, I found not even one that had the dots arranged in an X pattern.

(I believe the heads here are Minerva, goddess of wisdom. The owl is also associated with Minerva.)

Where's the quincunx that actually has a quincuncial arrangement of dots? Nowhere to be found, it seems. But everyone says it, so it must be true.

Addenda

• The first common use of “quincunx” as an English word was to refer to trees that were planted in a quincuncial pattern, although not necessarily in groups of exactly five, in which each square of four trees had a fifth at its center.

• Similarly, the Galton Box, has a quincuncial arrangement of little pegs. Galton himself called it a “quincunx”.

• The OED also offers this fascinating aside:

  Latin quincunx occurs earlier in an English context. Compare the following use apparently with reference to a v-shaped figure:

  1545 Decusis, tenne hole partes or ten Asses...It is also a fourme in any thynge representyng the letter, X, whiche parted in the middel, maketh an other figure called Quincunx, V.

  which shows that for someone, a quincuncial shape was a V and not an X, presumably because V is the Roman numeral for five.

  A decussis was a coin worth not ten uncia but ten asses, and it did indeed have an X on the front. A five-as coin was a quincussis and it had a V. I wonder if the author was confused?

  The source is Bibliotheca Eliotæ. The OED does not provide a page number.

• It wasn't until after I published this that I realized that today's date was the extremely quincuncial 2025-05-25. I thank the gods of chance and fortune for this little gift.

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The fivefold symmetry of the quince

The quince is so-named because, like other fruits in the apple family, it has a natural fivefold symmetry:

This is because their fruits develop from five-petaled flowers, and the symmetry persists through development. These are pear blossoms:

You can see this in most apples if you cut them into equatorial slices:

The fivefold symmetry isn't usually apparent from the outside once the structure leaves the flowering stage. But perfect Red Delicious specimens do have five little feet:

P.S.: I was just kidding about the name of the quince, which actually has nothing to do with any of this. It is a coincidence.

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