Moose are sensible creatures. I suspect that white moose do not believe they are superior to brown ones.

## Friday, August 18, 2017

### I Hope it is not an Alt-Right Moose

## Thursday, August 17, 2017

### Eclipses

### A Civil War Monument We Should Leave Up

## Friday, July 14, 2017

### Powers With Repetitions

^{3}expressed in base 12400?

And why is something like that really rare?

For the answer, you'll have to read my latest paper, co-written with Andrew Bridy, Robert J. Lemke Oliver, and Arlo Shallit.

## Wednesday, July 05, 2017

### Using a Decision Method to Prove a New Theorem in Number Theory

But Hilbert's dream was killed by Kurt Gödel and Alan Turing in the early 20th century. Gödel showed that, given any sufficiently powerful axiom system (roughly speaking, it's enough to be able to define addition and multiplication of integers), there would be true results lacking any formal proof. And Turing showed that, even if we restrict ourselves to *provable* results, there is no algorithm that, given a mathematical statement, will always halt and correctly report "provable" or "unprovable".

Nevertheless, there are some logical theories in which (a) every well-formed statement is provable or disprovable and (b) there is, in fact, an algorithm to find a proof or disproof. Such a theory is sometimes called *decidable* and the corresponding algorithm is called a *prover*. The first-order theory of the natural numbers with addition, often called Presburger arithmetic, is one such theory; it has a prover. Unfortunately, Presburger arithmetic is not very powerful, and although it has some practical applications, I am not aware of a single significant mathematical theorem proved using a Presburger prover.

However, when Presburger arithmetic is augmented with a certain additional function on natural numbers called *V*_{k}, for a fixed integer *k* ≥ 2, it remains decidable. And now it is powerful enough to prove things people really want to prove! My former master's student, Hamoon Mousavi, wrote a prover called Walnut for this bigger theory, and with it we have proven many new theorems of genuine mathematical interest. And we also reproved many results in the literature for which the only proofs previously known were long, tedious, and case-based.

Recently, my co-authors Aayush Rajasekaran and Tim Smith used a different method to algorithmically prove a new result in number theory. It concerns *palindromes*, which are numbers that, when considered as a string of digits in some integer base *b* ≥ 2, read the same forward and backwards. For example, the number 717 is a palindrome in base 10, but it is also a palindrome in base 2, since in binary it is 1011001101.

Last year, the number theorist William D. Banks started studying the additive number theory of palindromes. He proved that every natural number is the sum of at most 49 decimal palindromes. More recently, this result was improved by Florian Luca, Lewis Baxter, and the late Javier Cilleruelo, who proved that every natural number is the sum of at most 3 palindromes in base *b*, for all *b* ≥ 5. However, it seems that so far, nobody proved any bound at all for bases *b* = 2, 3, 4.

Here is our result: every natural number is the sum of at most 9 binary palindromes. The bound "9" is probably not the best possible result, as empirical results suggest the best possible bound is probably 4. Probably somebody will improve our bound soon! What makes our result interesting, though, is *how* we did it. Instead of the heavily case-based approach of Banks and Cilleruelo-Luca-Baxter, we used a decision method: we recoded the problem as a formal language theory problem, and then used the fact that this formalism has a decidable logical theory associated with it. Then we used publicly-available software to prove our result.

Here are the details: we created a certain kind of automaton, called a nondeterministic nested-word automaton, that takes integers *n*, represented in base 2, as input. Given an input representing an integer *n*, our automaton "guesses" a possible representation as a sum of palindromes, and then "verifies" that its guess is correct. Here the "verifies" means checking that the summands are indeed palindromes (read the same forwards and backwards) and that they sum to *n*. If the guess succeeds, the automaton accepts the input. Then the "sum of palindromes" theorem we want to prove amounts to claiming that the automaton accepts every possible natural number as input.

Luckily for us, the so-called "universality problem" (does a given automaton accept every input?) is actually decidable for nested word automata, a result proved by Alur and Madhusudan. We used the ULTIMATE automata library to then check the universality of the automaton we created. For more details, see our preprint.

Could other theorems in number theory be proved using this method? Yes, we proved a few more in our preprint. The holy grail would be a decidable logical theory strong enough to express traditional theorems about primes. If such a theory existed, we could, at least in theory, prove statements like Goldbach's conjecture (every even number > 2 is the sum of two primes) purely mechanically, by expressing them in the proper formalism and then running a prover. But currently we do not even know whether Presburger arithmetic, together with a predicate for primality, is decidable.

What's next? Well, a lot! But that will be the subject of Aayush's master's thesis, so you'll have to wait to find out.

## Saturday, July 01, 2017

### Bloom's Bizarro World

In today's visit, let us read this piece by one Nathan Schlueter, an academic so forgettable that I have already forgotten how to spell his last name. Prof. Schlueter is under the delusion that Allan Bloom's *The Closing of the American Mind* is not only an important book, it's so important that 30 years after its publication, it merits an entire *symposium*.

I read *The Closing of the American Mind* back in 2000, after someone recommended it to me. It was, to put it simply, a disaster. Bloom was a professor at the University of Chicago; we overlapped teaching there for a few years. At the time, focused on my own research, my only knowledge of him was the unflattering stories about him that I had heard from students.

It was apparent from nearly the first page of *Closing* that Bloom was a deeply troubled individual. His book, ostensibly a critique of higher education, was so clearly a rant based on Bloom's own intellectual and sexual insecurities that I found it almost painful to read. I wrote the following review for amazon back then, and here it is again, cleaned up a little:

*
This is not just a bad book. It is a sick one.
*

*
Bloom's obsessions are clear on almost every page: sex and rock music. Although clothed in a pretentious philosophical language, his objections betray what's really on his mind: he feels left out. The sexual revolution of the Sixties passed him by, and like the child whose playmates decide he's not good enough to get into the game, he retaliates by labelling everything about his opponents evil.
*

*
The poet Philip Larkin had Bloom's number when he wrote in his poem, Annus Mirabilis:
*

Sexual intercourse began

In nineteen sixty-three

(which was rather late for me)-

Between the end of the "Chatterley" ban

And the Beatles' first LP.
*
*

*
Like many neo-conservatives, Bloom doesn't really understand the principle of free speech. He says it "has given way to freedom of expression, in which the obscene gesture enjoys the same protected status as demonstrative discourse." In other words, freedom of speech should only apply to the stuff that Bloom approves of. (He also doesn't apparently know that the Canadian constitution guarantees "freedom of expression", precisely to avoid arbitrary Bloom-style distinctions.)
*

*
Like many professors in the humanities, he is deeply distrustful of science. And so he continues to push thinkers like Plato as essential to understanding the world, displaying no comprehension of the intellectual revolution brought by, for example, Charles Darwin. Is it still fruitful to read the Greeks? Certainly. But to pretend that we have learned nothing in 2000 years, that the insights of science play no part in an informed understanding of the world, is to play the part of the small child who insists, contrary to all evidence, that there is really is a Santa Claus.
*

*
Ultimately, this books tells us not about the mind of Americans, but rather the small, sanctimonious, and quite closed mind of one university professor named Allan Bloom.
*

*
*
It is no surprise at all that this Bloom Symposium is being published by Robert George's Witherspoon Institute, the very same place that funded and guided the Regnerus study on gay parents, a laughable piece of scholarship that just so happened to confirm Robert George's own negative view of homosexuality.

These folks have *very* closed minds, and their natural habitat is a setting where their prejudices can be confirmed and clothed in academic respectability.

## Saturday, May 27, 2017

### I Am The Yeggman

According to the OED, a "yegg" is a burglar or safe-breaker, and its etymology is given as "Said to be the surname of a certain American burglar and safe-breaker."

The earliest citations given in the OED are

*1903 N.Y. Evening Post 23 June (Cent. D. Supp.), The prompt breaking up of the organized gangs of professional beggars and yeggs.
*

*
1905 N.Y. Times 2 Jan. (Cent. Dict. Suppl.), Detective Sergeants..captured on the Bowery three men who, they say, are among the most successful ‘yeggmen’, or safe~crackers, in the business.
*

A related word is "yeggman":

*
1906 A. Stringer Wire Tappers 100 ‘Now, nitro-glycerine I object to, it's so abominably crude.’.. ‘And so odiously criminal!’ she interpolated. ‘Precisely. We're not exactly yeggmen yet.’
*

However, using a newspaper database, I found several earlier citations:

Minneapolis *Star-Tribune*, November 25 1899, p. 12: *...for Mr. Alness did not know until the detectives told him that "John Yegg & Co." is a bit of thieves' slang, "yegg" standing for one who is ready to beg or steal, stealing preferred as more honorable...
*

Bloomington, IL

*Pantagraph*, December 28 1899, p. 3:

*The gang ... numbers at least twenty-five members, who call themselves Yeggmen.*

New York

*Sun*, January 22 1900, p. 2:

*Four crooks, whom the Pinkerton agents describe as hobo safe burglars belonging to a new fraternity known as "Yeggs," were arrested in Newark last Thursday night...*

The uncommon words "yegg", "yeggs", "yeggman", "yeggmen" reached the zenith of their popularity around 1920-1935 and are only rarely used today. Here is a google ngram search:

## Monday, April 17, 2017

### Uncommon Descent Lies Again

*Uncommon Descent*is, of course, one of the two main propaganda arms of the intelligent design movement --- the other one being "Evolution News". Since the ID movement is essentially based on religious dogma and deception, it's no surprise that these blogs have a large amount of fake content. But I am always surprised at how

*shamelessly*they mislead.

One of the recent entries at *Uncommon Descent* is a good example. They refer to a 1980 article of Hamming entitled "The Unreasonable Effectiveness of Mathematics". It's not hard for anyone to verify that what I just wrote is the correct title of Hamming's article; indeed, the full text of the article is easily available online.

I am not going to criticize Hamming's article in much detail here. There is much that is good in it, but I feel his final conclusion is unmerited. On what rigorous basis can we measure how effective mathematics is, and on what basis are we allowed to conclude that the effectiveness we observe is "unreasonable"? It seems purely a matter of personal taste.

My own personal taste is that mathematics is remarkably *ineffective*, because the vast majority of events that we see in the physical world are quite difficult to model accurately. If we release a single tritium atom in a lecture hall at 10:00 AM, where will it be at 11:00 AM? No physicist in the world can tell you with very much precision.

Similarly, Hamming asks, "How can it be that simple mathematics, being after all a product of the human mind, can be so remarkably useful in so many widely different situations?" Well, lots of mathematics is *not* remarkably useful. Much of what I personally do has little real-life application. So how can we measure, in a precise way, when that usefulness is "remarkable" and when it is not? Hamming does not tell us. My own personal view is that humans tend to use what is effective and discard what is not. If, for example, dancing were more effective in describing the physical world, scientists would be ballerinas.

In any event, Hamming's observations are not my main point. My main point is that, at *Uncommon Descent* the title of Hamming's article has been altered from "The Unreasonable Effectiveness of Mathematics" to "The Unreasonable Effectiveness of Mathematics vs. Evolution". Whether this change is a matter of deliberate deception or pure incompetence, I am not certain. But it *is* part of a larger pattern that we see repeated.