Mathematical research traditionally involves a small number of professional mathematicians working closely on difficult problems. However, I have long believed that there is a complementary way to do mathematics, in which one works with a broad community of mathematically minded people on problems which may not be as deep as the problems one traditionally works on, but still are of mathematical interest; and that modern technologies, including AI, are more suitable for contributing the latter type of workflow. The “Polymath projects” were one example of this broad type of collaboration, where internet platforms such as blogs and wikis were used to facilitate such collaboration. Some years later, collaborative formalization projects (such as the one to formalize the Polynomial Freiman–Ruzsa conjecture of Marton, discussed previously on this blog here) became popular in some circles. And in 2024, I launched the Equational Theories Project (ETP) (discussed on this blog here and here), combining the rigor of Lean formalization with “good old fashioned AI” (in the form of automated theorem provers) to settle (with formal verification) over 22 million true-false problems in universal algebra.

Continuing in this spirit, Damek Davis and I are launching a new project, in the form of an experimental competitive challenge hosted by the SAIR Foundation (where I serve as a board member, and which is supplying technical support and compute). The idea of this challenge, motivated in part by this recent paper of Honda, Murakami, and Zhang, is to measure the extent to which the 22 million universal algebra true-false results obtained by the ETP can be “distilled” into a short, human-readable “cheat sheet”, similar to how a student in an undergraduate math class might distill the knowledge learned from that class into a single sheet of paper that the student is permitted to bring into an exam.

Here is a typical problem in universal algebra that the ETP was able to answer:

Problem 1 Suppose that {*: M \times M \rightarrow M} is a binary operation such that {x * (y * z) = (z * w) * w} for all {x,y,z,w}. Is it true that {x * (y * x) = (x * y) * z} for all {x,y,z}?

Such a problem can be settled either by algebraically manipulating the initial equation to deduce the target equation, or by finding a counterexample to the target equation that still satisfies the initial equation. There are a variety of techniques to achieve either of these, but this sort of problem is difficult, and even undecidable in some cases; see this paper of the ETP collaborators for more discussion. Nevertheless, many of these problems can be settled with some effort by humans, by automated theorem provers, or by frontier AI systems; here for instance is an AI-generated solution to the above problem.

However, these AI models are expensive, and do not reveal much insight as to where their answers come from. If one instead tries a smaller and cheaper model, such as one of the many open-source models available, it turns out that these models basically perform no better than random chance, in that when asked to say whether the answer to a question such as the above is true or false, they only answer correctly about 50% of the time.

But, similarly to how a student struggling with the material for a math class can perform better on an exam when provided the right guidance, it turns out that such cheap models can perform at least modestly better on this task (with success rates increasing to about 55%-60%) if given the right prompt or “cheat sheet”.

“Stage 1” of the distillation challenge, which we launched today, asks for contestants to design a cheat sheet (of at most 10 kilobytes in size) that can increase the performance of these models on the above true-false problems to as high a level as possible. We have provided a “playground” with which to test one’s cheat sheet (or a small number of example cheat sheets) some cheap models against a public set of 1200 problems (1000 of which were randomly selected, and rather easy, together with 200 “hard” problems that were selected to resist the more obvious strategies for resolving these questions); a brief video explaining how to use the playground can be found here.

Submissions stage will end on April 20, after which we will evaluate the submissions against a private subset of test questions. The top 1000 submissions will advance to a second stage which we are currently in the process of designing, which will involve more advanced models, but also the more difficult task of not just providing a true-false answer, but also a proof or counterexample to the problem.

The competition will be coordinated on this Zulip channel, where I hope there will be a lively and informative discussion.

My hope is that the winning submissions will capture the most productive techniques for solving these problems, and/or provide general problem-solving techniques that would also be applicable to other types of mathematical problems. We started with the equational theory project data set for this pilot competition due to its availability and spectrum of difficulty levels, but if this type of distillation process leads to interesting results, one could certainly run in on many other types of mathematical problem classes to get some empirical data on how readily they can be solved, particularly after we learn from this pilot competition on how to encourage participation and share of best practices.

SAIR will also launch some other mathematical challenges in the coming months that will be of a more cooperative nature than this particular competitive challenge; stay tuned for further announcements.

[This post is written in my capacity as Vice-Chair of the Board of Trustees of SLMath. -T.]

SLMath, formerly MSRI, has launched the search for the next Deputy Director. This key position is a close advisor to the Director and shares in the internal management of the scientific team and programs at SLMath. This position is ideal for an experienced professional with a PhD in mathematical sciences seeking a new opportunity to leverage their strengths in program and grant management, financial management, and people management.

Just a brief announcement that I have been working with Quanta Books to publish a short book in popular mathematics entitled “Six Math Essentials“, which will cover six of the fundamental concepts in mathematics — numbers, algebra, geometry, probability, analysis, and dynamics — and how they connect with our real-world intuition, the history of math and science, and to modern practice of mathematics, both in theory and in applications. The scheduled publication date is Oct 27, but it is currently available for preorder.

(Sharing this in my capacity of director of special projects at IPAM.)

IPAM is holding an Industrial Short Course on Generative AI Algorithms on March 5-6, 2026.

The short course is aimed at people from industry or government who want to get started in deep learning, apply deep learning to their projects, learn how to code deep learning algorithms, and upgrade their skills to the latest AI algorithms, including generative AI. The course will be taught be Professor Xavier Bresson from the Department of Computer Science at the National University of Singapore (NUS).

The course will be limited to 25 participants. The fee for this course is $2,500 for participants. Registration closes soon (Feb 5); we still have a few spots available.

Thomas Bloom’s Erdös problem site has become a real hotbed of activity in recent months, particularly as some of the easiest of the outstanding open problems have turned out to be amenable to various AI-assisted approaches; there is now a lively community in which human contributions, AI contributions, and hybrid contributions are presented, discussed, and in some cases approved as updates to the site.

One of the lessons I draw from this is that once a well curated database of precise mathematical problems is maintained, it becomes possible for other parties to build upon it in many ways (including both AI-based and human-based approaches), to systematically make progress on some fraction of the problems.

This makes me wonder what other mathematical databases could be created to stimulate similar activity. One candidate that came to mind are “optimization constants” – constants {C} that arise from some mathematical optimization problem of interest, for instance finding the best constant {C} for which a certain functional inequality is satisfied.

I am therefore proposing to create a crowdsourced repository for such constants, to record the best upper and lower bounds known for any given such constant, in order to help encourage efforts (whether they be by professional mathematicians, amateur mathematicians, or research groups at a tech company) to try to improve upon the state of the art.

There are of course thousands of such constants one could consider, but just to set the discussion going, I set up a very minimal, proof of concept Github repository holding over 20 constants including:

  1. {C_{1a}}, the constant in a certain autocorrelation quantity relating to Sidon sets. (This constant seems to have a surprisingly nasty optimizer; see this tweet thread of Damek Davis.)
  2. {C_{1b}}, the constant in Erdös’ minimum overlap problem.

Here, I am taking inspiration from the Erdös problem web site and arbitrarily assigning a number to each constant, for ease of reference.

Even in this minimal state I think the repository is ready to start accepting more contributions, in the form of pull requests that add new constants, or improve the known bounds on existing constants. (I am particularly interested in constants that have an extensive literature of incremental improvements in the lower and upper bounds, and which look at least somewhat amenable to computational or AI-assisted approaches.) But I would be interested to hear feedback on how to improve the repository in other ways.

Update: Paata Ivanisvili and Damek Davis have kindly agreed to help run and expand this repository.

A basic problem in sieve theory is to understand what happens when we start with the integers {{\bf Z}} (or some subinterval of the integers) and remove some congruence classes {a_i \pmod{q_i}} for various moduli {q_i}. Here we shall concern ourselves with the simple setting where we are sieving the entire integers rather than an interval, and are only removing a finite number of congruence classes {a_1 \pmod{q_1}, \ldots, a_k \pmod{q_k}}. In this case, the set of integers that remain after the sieving is periodic with period {Q = \mathrm{lcm}(q_1,\dots,q_k)}, so one work without loss of generality in the cyclic group {{\bf Z}/Q{\bf Z}}. One can then ask: what is the density of the sieved set

\displaystyle  \{ n \in {\bf Z}/Q{\bf Z}: n \neq a_i \hbox{ mod } q_i \hbox{ for all } i=1,\ldots,k \}? \ \ \ \ \ (1)

If the {q_i} were all coprime, then it is easy to see from the Chinese remainder theorem that the density is given by the product

\displaystyle  \prod_{i=1}^k \left(1 - \frac{1}{q_i}\right).

However, when the {q_i} are not coprime, the situation is more complicated. One can use the inclusion-exclusion formula to get a complicated expression for the density, but it is not easy to work with. Sieve theory also supplies one with various useful upper and lower bounds (starting with the classical Bonferroni inequalities), but do not give exact formulae.

In this blog post I would like to note one simple fact, due to Rogers, that one can say about this problem:

Theorem 1 (Rogers’ theorem) For fixed {q_1,\dots,q_k}, the density of the sieved set is maximized when all the {a_i} vanish. Thus,

\displaystyle  |\{ n \in {\bf Z}/Q{\bf Z}: n \neq a_i \hbox{ mod } q_i \hbox{ for all } i=1,\ldots,k \}|

\displaystyle \leq |\{ n \in {\bf Z}/Q{\bf Z}: n \neq 0 \hbox{ mod } q_i \hbox{ for all } i=1,\ldots,k \}|.

Example 2 If one sieves out {1 \pmod{2}}, {1 \pmod{3}}, and {2 \pmod{6}}, then only {0 \pmod{6}} remains, giving a density of {1/6}. On the other hand, if one sieves out {0 \pmod{2}}, {0 \pmod{3}}, and {0 \pmod{6}}, then the remaining elements are {1} and {5 \pmod{6}}, giving the larger density of {2/6}.

This theorem is somewhat obscure: its only appearance in print is in pages 242-244 of this 1966 text of Halberstam and Roth, where the authors write in a footnote that the result is “unpublished; communicated to the authors by Professor Rogers”. I have only been able to find it cited in three places in the literature: in this 1996 paper of Lewis, in this 2007 paper of Filaseta, Ford, Konyagin, Pomerance, and Yu (where they credit Tenenbaum for bringing the reference to their attention), and is also briefly mentioned in this 2008 paper of Ford. As far as I can tell, the result is not available online, which could explain why it is rarely cited (and also not known to AI tools). This became relevant recently with regards to Erdös problem 281, posed by Erdös and Graham in 1980, which was solved recently by Neel Somani through an AI query by an elegant ergodic theory argument. However, shortly after this solution was located, it was discovered by KoishiChan that Rogers’ theorem reduced this problem immediately to a very old result of Davenport and Erdös from 1936. Apparently, Rogers’ theorem was so obscure that even Erdös was unaware of it when posing the problem!

Modern readers may see some similarities between Rogers’ theorem and various rearrangement or monotonicity inequalites, suggesting that the result may be proven by some sort of “symmetrization” or “compression” method. This is indeed the case, and is basically Rogers’ original proof. We can modernize a bit as follows. Firstly, we can abstract {{\bf Z}/Q{\bf Z}} into a finite cyclic abelian group {G}, with residue classes now becoming cosets of various subgroups of {G}. We can take complements and restate Rogers’ theorem as follows:

Theorem 3 (Rogers’ theorem, again) Let {a_1+H_1, \dots, a_k+H_k} be cosets of a finite cyclic abelian group {G}. Then

\displaystyle  |\bigcup_{j=1}^k a_j + H_j| \geq |\bigcup_{j=1}^k H_j|.

Example 4 Take {G = {\bf Z}/6{\bf Z}}, {H_1 = 2{\bf Z}/6{\bf Z}}, {H_2 = 3{\bf Z}/6{\bf Z}}, and {H_3 = 6{\bf Z}/6{\bf Z}}. Then the cosets {1 + H_1}, {1 + H_2}, and {2 + H_3} cover the residues {\{1,2,3,4,5\}}, with a cardinality of {5}; but the subgroups {H_1,H_2,H_3} cover the residues {\{0,2,3,4\}}, having the smaller cardinality of {4}.

Intuitively: “sliding” the cosets {a_i+H_i} together reduces the total amount of space that these cosets occupy. As pointed out in comments, the requirement of cyclicity is crucial; four lines in a finite affine plane already suffice to be a counterexample otherwise.

By factoring the cyclic group into p-groups, Rogers’ theorem is an immediate consequence of two observations:

Theorem 5 (Rogers’ theorem for cyclic groups of prime order) Rogers’ theorem holds when {G = {\bf Z}/p^n {\bf Z}} for some prime power {p^n}.

Theorem 6 (Rogers’ theorem preserved under products) If Rogers’ theorem holds for two finite abelian groups {G_1, G_2} of coprime orders, then it also holds for the product {G_1 \times G_2}.

The case of cyclic groups of prime order is trivial, because the subgroups of {G} are totally ordered. In this case {\bigcup_{j=1}^k H_j} is simply the largest of the {H_j}, which has the same size as {a_j + H_j} and thus has lesser or equal cardinality to {\bigcup_{j=1}^k a_j + H_j}.

The preservation of Rogers’ theorem under products is also routine to verify. By the coprime orders of {G_1,G_2} and standard group theoretic arguments (e.g., Goursat’s lemma, the Schur–Zassenhaus theorem, or the classification of finite abelian groups), one can see that any subgroup {H_j} of {G_1 \times G_2} splits as a direct product {H_j = H_{j,1} \times H_{j,2}} of subgroups of {G_1,G_2} respectively, so the cosets {a_j + H_j} also split as

\displaystyle  a_j + H_j = (a_{j,1} + H_{j,1}) \times (a_{j,2} + H_{j,2}).

Applying Rogers’ theorem for {G_2} to each “vertical slice” of {G_1 \times G_2} and summing, we see that

\displaystyle  |\bigcup_{j=1}^k (a_{j,1} + H_{j,1}) \times (a_{j,2} + H_{j,2})| \geq |\bigcup_{j=1}^k (a_{j,1} + H_{j,1}) \times H_{j,2}|

and then applying Rogers’ theorem for {G_1} to each “horizontal slice” of {G_1 \times G_2} and summing, we obtain

\displaystyle  |\bigcup_{j=1}^k (a_{j,1} + H_{j,1}) \times H_{j,2}| \geq |\bigcup_{j=1}^k H_{j,1} \times H_{j,2}|.

Combining the two inequalities, we obtain the claim.

Like many other areas of modern analysis, analytic number theory often relies on the convenient device of asymptotic notation to express its results. It is common to use notation such as {X = O(Y)} or {X \ll Y}, for instance, to indicate a bound of the form {|X| \leq C Y} for some unspecified constant {C}. Such implied constants {C} vary from line to line, and in most papers, one does not bother to compute them explicitly. This makes the papers easier both to write and to read (for instance, one can use asymptotic notation to conceal a large number of lower order terms from view), and also means that minor numerical errors (for instance, forgetting a factor of two in an inequality) typically has no major impact on the final results. However, the price one pays for this is that many results in analytic number theory are only true in asymptotic sense; a typical example is Vinogradov’s theorem that every sufficiently large odd integer can be expressed as the sum of three primes. In the first few proofs of this theorem, the threshold for “sufficiently large” was not made explicit.

There is however a small portion of the analytic number theory devoted to explicit analytic number theory estimates, in which all constants are made completely explicit (and many lower order terms are retained). For instance, whereas the prime number theorem asserts that the prime counting function {\pi(x)} is asymptotic to the logarithmic integral {\mathrm{Li}(x) = \int_2^x \frac{dt}{\log t}}, in this recent paper of Fiori, Kadiri, and Swidinsky the explicit estimate

\displaystyle  |\pi(x) - \mathrm{Li}(x)| \leq 9.2211 x \sqrt{\log x} \exp(- 0.8476 \sqrt{\log x} )

is proven for all {x \geq 2}.

Such explicit results follow broadly similar strategies of proof to their non-explicit counterparts, but require a significant amount of careful book-keeping and numerical optimization; furthermore, any given explicit analytic number theory paper is likely to rely on the numerical results obtained in previous explicit analytic number theory papers. While the authors make their best efforts to avoid errors and build in some redundancy into their work, there have unfortunately been a few cases in which an explicit result stated in the published literature contained numerical errors that placed the numerical constants in several downstream applications of these papers into doubt.

Because of this propensity for error, updating any given explicit analytic number theory result to take into account computational improvements in other explicit results (such as zero-free regions for the Riemann zeta function) is not done lightly; such updates occur on the timescale of decades, and only by a small number of specialists in such careful computations. This leads to authors needing such explicit results to often be forced to rely on papers that are a decade or more out of date, with constants that they know in principle can be improved by inserting more recent explicit inputs, but do not have the domain expertise to confidently update all the numerical coefficients.

To me, this situation sounds like an appropriate application of modern AI and formalization tools – not to replace the most enjoyable aspects of human mathematical research, but rather to allow extremely tedious and time-consuming, but still necessary, mathematical tasks to be offloaded to semi-automated or fully automated tools.

Because of this, I (acting in my capacity as Director of Special Projects at IPAM) have just launched the integrated explicit analytic number theory network, a project partially hosted within the existing “Prime Number Theorem And More” (PNT+) formalization project. This project will consist of two components. The first is a crowdsourced formalization project to formalize a number of inter-related explicit analytic number theory results in Lean, such as the explicit prime number theorem of Fiori, Kadiri, and Swidinsky mentioned above; already some smaller results have been largely formalized, and we are making good progress (especially with the aid of modern AI-powered autoformalization tools) on several of the larger papers. The second, which will be run at IPAM with the financial and technical support of Math Inc., will be to extract from this network of formalized results an interactive “spreadsheet” of a large number of types of such estimates, with the ability to add or remove estimates from the network and have the numerical impact of these changes automatically propagate to other estimates in the network, similar to how changing one cell in a spreadsheet will automatically update other cells that depend on it. For instance, one could increase or decrease the numerical threshold to which the Riemann hypothesis is verified, and see the impact of this change on the explicit error terms in the prime number theorem; or one could “roll back” all the literature to a given date, and see what the best estimates on various analytic number theory expressions could still be derived from the literature available at that date. Initially, this spreadsheet will be drawn from direct adaptations of the various arguments from papers formalized within the network, but in a more ambitious second stage of the project we plan to use AI tools to modify these arguments to find more efficient relationships between the various numerical parameters than were provided in the source literature.

These more ambitious outcomes will likely take several months before a working proof of concept can be demonstrated; but in the near term I will be grateful for any contributions to the formalization side of the project, which is being coordinated on the PNT+ Zulip channel and on the github repository. We are using a github issues based system to coordinate the project, similar to how it was done for the Equational Theories Project. Any volunteer can select one of the outstanding formalization tasks on the Github issues page and “claim” it as a task to work on, eventually submitting a pull request (PR) to the repository when proposing a solution (or to “disclaim” the task if for whatever reason you are unable to complete it). As with other large formalization projects, an informal “blueprint” is currently under construction that breaks up the proofs of the main results of several explicit analytic number theory papers into bite-sized lemmas and sublemmas, most of which can be formalized independently without requiring broader knowledge of the arguments from the paper that the lemma was taken from. (A graphical display of the current formalization status of this blueprint can be found here. At the current time of writing, many portions of the blueprint are disconnected from each other, but as the formalization progresses, more linkages should be created.)

One minor innovation implemented in this project is to label each task by a “size” (ranging from XS (extra small) to XL (extra large)) that is a subjective assessment of the task difficulty, with the tasks near the XS side of the spectrum particularly suitable for beginners to Lean.

We are permitting AI use in completing the proof formalization tasks, though we require the AI use to be disclosed, and that the code is edited by humans to remove excessive bloat. (We expect some of the AI-generated code to be rather inelegant; but no proof of these explicit analytic number theory estimates, whether human-generated or AI-generated, is likely to be all that pretty or worth reading for its own sake, so the downsides of using AI-generated proofs here are lower than in other use cases.) We of course require all submissions to typecheck correctly in Lean through Github’s Continuous Integration (CI) system, so that any incorrect AI-generated code will be rejected. We are also cautiously experimenting with ways in which AI can also automatically or semi-automatically generate the formalized statements of lemmas and theorems, though here one has to be significantly more alert to the dangers of misformalizing an informally stated result, as this type of error cannot be automatically detected by a proof assistant.

We also welcome suggestions for additional papers or results in explicit analytic number theory to add to the network, and will have some blueprinting tasks in addition to the formalization tasks to convert such papers into a blueprinted sequence of small lemmas suitable for individual formalization.

Update: a personal log documenting the project may be found here.

Asgar Jamneshan, Or Shalom and I have uploaded to the arXiv our paper “ Polynomial towers and inverse Gowers theory for bounded-exponent groups“. This continues our investigation into the ergodic-theory approach to the inverse theory of Gowers norms over finite abelian groups {G}. In this regard, our main result establishes a satisfactory (qualitative) inverse theorem for groups {G} of bounded exponent:

Theorem 1 Let {G} be a finite abelian group of some exponent {m}, and let {f: G \rightarrow {\bf C}} be {1}-bounded with {\|f\|_{U^{k+1}(G)} > \delta}. Then there exists a polynomial {P: G \rightarrow {\bf R}/{\bf Z}} of degree at most {k} such that

\displaystyle  |\mathop{\bf E}_{x \in G} f(x) e(-P(x))| \gg_{k,m,\delta} 1.

This type of result was previously known in the case of vector spaces over finite fields (by work of myself and Ziegler), groups of squarefree order (by work of Candela, González-Sánchez, and Szegedy), and in the {k \leq 2} case (by work of Jamneshan and myself). The case {G = ({\bf Z}/4{\bf Z})^n}, for instance, is treated by this theorem but not covered by previous results. In the aforementioned paper of Candela et al., a result similar to the above theorem was also established, except that the polynomial {P} was defined in an extension of {G} rather than in {G} itself (or equivalently, {f} correlated with a projection of a phase polynomial, rather than directly with a phase polynomial on {G}). This result is consistent with a conjecture of Jamneshan and myself regarding what the “right” inverse theorem should be in any finite abelian group {G} (not necessarily of bounded exponent).

In contrast to previous work, we do not need to treat the “high characteristic” and “low characteristic” cases separately; in fact, many of the delicate algebraic questions about polynomials in low characteristic do not need to be directly addressed in our approach, although this is at the cost of making the inductive arguments rather intricate and opaque.

As mentioned above, our approach is ergodic-theoretic, deriving the above combinatorial inverse theorem from an ergodic structure theorem of Host–Kra type. The most natural ergodic structure theorem one could establish here, which would imply the above theorem, would be the statement that if {\Gamma} is a countable abelian group of bounded exponent, and {X} is an ergodic {\Gamma}-system of order at most {k} in the Host–Kra sense, then {X} would be an Abramov system – generated by polynomials of degree at most {k}. This statement was conjectured many years ago by Bergelson, Ziegler, and myself, and is true in many “high characteristic” cases, but unfortunately fails in low characteristic, as recently shown by Jamneshan, Shalom, and myself. However, we are able to recover a weaker version of this statement here, namely that {X} admits an extension which is an Abramov system. (This result was previously established by Candela et al. in the model case when {\Gamma} is a vector space over a finite field.) By itself, this weaker result would only recover a correlation with a projected phase polynomial, as in the work of Candela et al.; but the extension we construct arises as a tower of abelian extensions, and in the bounded exponent case there is an algebraic argument (hinging on a certain short exact sequence of abelian groups splitting) that allows one to map the functions in this tower back to the original combinatorial group {G} rather than an extension thereof, thus recovering the full strength of the above theorem.

It remains to prove the ergodic structure theorem. The standard approach would be to describe the system {X} as a Host–Kra tower

\displaystyle  Z^{\leq 0}(X) \leq Z^{\leq 1}(X) \leq \dots \leq Z^{\leq k}(X) = X,

where each extension {Z^{\leq j+1}(X)} of {Z^{\leq j}(X)} is a compact abelian group extension by a cocycle of “type” {j}, and them attempt to show that each such cocycle is cohomologous to a polynomial cocycle. However, this appears to be impossible in general, particularly in low characteristic, as certain key short exact sequences fail to split in the required ways. To get around this, we have to work with a different tower, extending various levels of this tower as needed to obtain additional good algebraic properties of each level that enables one to split the required short exact sequences. The precise properties needed are rather technical, but the main ones can be described informally as follows:

  • We need the cocycles to obey an “exactness” property, in that there is a sharp correspondence between the type of the cocycle (or any of its components) and its degree as a polynomial cocycle. (By general nonsense, any polynomial cocycle of degree {\leq d-1} is automatically of type {\leq d}; exactness, roughly speaking, asserts the converse.) Informally, the cocycles should be “as polynomial as possible”.
  • The systems in the tower need to have “large spectrum” in that the set of eigenvalues of the system form a countable dense subgroup of the Pontryagin dual of the acting group {\Gamma} (in fact we demand that a specific countable dense subgroup {\tilde \Gamma} is represented).
  • The systems need to be “pure” in the sense that the sampling map {\iota_{x_0} P(\gamma) := P(T^\gamma x_0)} that maps polynomials on the system to polynomials on the group {\Gamma} is injective for a.e. {x_0}, with the image being a pure subgroup. Informally, this means that the problem of taking roots of a polynomial in the system is equivalent to the problem of taking roots of the corresponding polynomial on the group {\Gamma}. In low characteristic, the root-taking problem becomes quite complicated, and we do not give a good solution to this problem either in the ergodic theory setting or the combinatorial one; however, purity at least lets one show that the two problems are (morally) equivalent to each other, which turns out to be what is actually needed to make the arguments work. There is also a technical “relative purity” condition we need to impose at each level of the extension to ensure that this purity property propagates up the tower, but I will not describe it in detail here.

It is then possible to recursively construct a tower of extensions that eventually reaches an extension of {X}, for which the above useful properties of exactness, large spectrum, and purity are obeyed, and that the system remains Abramov at each level of the tower. This requires a lengthy process of “straightening” the cocycle by differentiating it, obtaining various “Conze–Lesigne” type equations for the derivatives, and then “integrating” those equations to place the original cocycle in a good form. At multiple stages in this process it becomes necessary to have various short exact sequences of (topological) abelian groups split, which necessitates the various good properties mentioned above. To close the induction one then has to verify that these properties can be maintained as one ascends the tower, which is a non-trivial task in itself.

I’ve just uploaded to the arXiv my preprint The maximal length of the Erdős–Herzog–Piranian lemniscate in high degree. This paper resolves (in the asymptotic regime of sufficiently high degree) an old question about the polynomial lemniscates

\displaystyle  \partial E_1(p) := \{ z: |p(z)| = 1\}

attached to monic polynomials {p} of a given degree {n}, and specifically the question of bounding the arclength {\ell(\partial E_1(p))} of such lemniscates. For instance, when {p(z)=z^n}, the lemniscate is the unit circle and the arclength is {2\pi}; this in fact turns out to be the minimum possible length amongst all (connected) lemniscates, a result of Pommerenke. However, the question of the largest lemniscate length is open. The leading candidate for the extremizer is the polynomial

\displaystyle  p_0(z)= z^n-1

whose lemniscate is quite convoluted, with an arclength that can be computed asymptotically as

\displaystyle  \ell(\partial E_1(p_0)) = B(1/2,n/2) = 2n + 4 \log 2 + O(1/n)

where {B} is the beta function.

Image

(The images here were generated using AlphaEvolve and Gemini.) A reasonably well-known conjecture of Erdős, Herzog, and Piranian (Erdős problem 114) asserts that this is indeed the maximizer, thus {\ell(\partial E_1(p)) \leq \ell(\partial E_1(p_0))} for all monic polynomials of degree {n}.

There have been several partial results towards this conjecture. For instance, Eremenko and Hayman verified the conjecture when {n=2}. Asympotically, bounds of the form {\ell(\partial E_1(p)) \leq (C+o(1)) n} had been known for various {C} such as {\pi}, {2\pi}, or {4\pi}; a significant advance was made by Fryntov and Nazarov, who obtained the asymptotically sharp upper bound

\displaystyle  \ell(\partial E_1(p)) \leq 2n + O(n^{7/8})

and also obtained the sharp conjecture {\ell(\partial E_1(p)) \leq \ell(\partial E_1(p_0))} for {p} sufficiently close to {p_0}. In that paper, the authors comment that the {O(n^{7/8})} error could be improved, but that {O(n^{1/2})} seemed to be the limit of their method.

I recently explored this problem with the optimization tool AlphaEvolve, where I found that when I assigned this tool the task of optimizing {\ell(\partial E_1(p))} for a given degree {n}, that the tool rapidly converged to choosing {p} to be equal to {p_0} (up to the rotation and translation symmetries of the problem). This suggested to me that the conjecture was true for all {n}, though of course this was far from a rigorous proof. AlphaEvolve also provided some useful visualization code for these lemniscates which I have incorporated into the paper (and this blog post), and which helped build my intuition for this problem; I view this sort of “vibe-coded visualization” as another practical use-case of present-day AI tools.

In this paper, we iteratively improve upon the Fryntov-Nazarov method to obtain the following bounds, in increasing order of strength:

  • (i) {\ell(\partial E_1(p)) \leq 2n + O(n^{1/2})}.
  • (ii) {\ell(\partial E_1(p)) \leq 2n + O(1)}.
  • (iii) {\ell(\partial E_1(p)) \leq 2n + 4 \log 2 + o(1)}.
  • (iv) {\ell(\partial E_1(p)) \leq \ell(\partial E_1(p_0))} for sufficiently large {n}.
In particular, the Erdős–Herzog–Piranian conjecture is now verified for sufficiently large {n}.

The proof of these bounds is somewhat circuitious and technical, with the analysis from each part of this result used as a starting point for the next one. For this blog post, I would like to focus on the main ideas of the arguments.

A key difficulty is that there are relatively few tools for upper bounding the arclength of a curve; indeed, the coastline paradox already shows that curves can have infinite length even when bounded. Thus, one needs to utilize some smooth or algebraic structure on the curve to hope for good upper bounds. One possible approach is via the Crofton formula, using Bezout’s theorem to control the intersection of the curve with various lines. This is already good enough to get bounds of the form {\ell(\partial E_1(p)) \leq O(n)} (for instance by combining it with other known tools to control the diameter of the lemniscate), but it seems challenging to use this approach to get bounds close to the optimal {\sim 2n}.

Instead, we follow Fryntov–Nazarov and utilize Stokes’ theorem to convert the arclength into an area integral. A typical identity used in that paper is

\displaystyle  \ell(\partial E_1(p)) = 2 \int_{E_1(p)} |p'|\ dA - \int_{E_1(p)} \frac{|p\varphi|}{\varphi} \psi\ dA

where {dA} is area measure, {\varphi = p'/p} is the log-derivative of {p}, {\psi = p''/p'} is the log-derivative of {p'}, and {E_1(p)} is the region {\{ |p| \leq 1 \}}. This and the triangle inequality already lets one prove bounds of the form {\ell(\partial E_1(p)) \leq 2\pi n + O(n^{1/2})} by controlling {\int_{E_1(p)} |\psi|\ dA} using the triangle inequality, the Hardy-Littlewood rearrangement inequality, and the Polya capacity inequality.

But this argument does not fully capture the oscillating nature of the phase {\frac{|\varphi|}{\varphi}} on one hand, and the oscillating nature of {E_1(p)} on the other. Fryntov–Nazarov exploited these oscillations with some additional decompositions and integration by parts arguments. By optimizing these arguments, I was able to establish an inequality of the form

\displaystyle  \ell(\partial E_1(p)) \leq \frac{1}{\pi} \int_{E_2(p)} |\psi|\ dA + O(X_1+X_2+X_3+X_4+X_5) \ \ \ \ \ (1)

where {E_2(p) = \{ |p| \leq 2\}} is an enlargement of {E_1(p)} (that is significantly less oscillatory, as displayed in the figure below), and {X_1,\dots,X_5} are certain error terms that can be controlled by a number of standard tools (e.g., the Grönwall area theorem).

One can heuristically justify (1) as follows. Suppose we work in a region where the functions {\psi}, {p} are roughly constant: {\psi(z) \approx \psi_0}, {p(z) \approx c_0}. For simplicity let us normalize {\psi_0} to be real, and {c_0} to be negative real. In order to have a non-trivial lemniscate in this region, {c_0} should be close to {-1}. Because the unit circle {\partial D(0,1)} is tangent to the line {\{ w: \Re w = -1\}} at {-1}, the lemniscate condition {|p(z)|=1} is then heuristically approximated by the condition that {\Re (p(z) + 1) = 0}. On the other hand, the hypothesis {\psi(z) \approx \psi_0} suggests that {p'(z) \approx A e^{\psi_0 z}} for some amplitude {z}, which heuristically integrates to {p(z) \approx c_0 + \frac{A}{\psi_0} e^{\psi_0 z}}. Writing {\frac{A}{\psi_0}} in polar coordinates as {Re^{i\theta}} and {z} in Cartesian coordinates as {x+iy}, the condition {\Re(p(z)+1)=0} can then be rearranged after some algebra as

\displaystyle  \cos (\psi_0 y + \theta) \approx -\frac{1+c_0}{Re^{\psi_0 x}}.

If the right-hand side is much larger than {1} in magnitude, we thus expect the lemniscate to be empty in this region; but if instead the right-hand side is much less than {1} in magnitude, we expect the lemniscate to behave like a periodic sequence of horizontal lines of spacing {\frac{\pi}{\psi_0}}. This makes the main terms on both sides of (1) approximately agree (per unit area).

A graphic illustration of (1) (provided by Gemini) is shown below, where the dark spots correspond to small values of {\psi} that act to “repel” (and shorten) the lemniscate. (The bright spots correspond to the critical points of {p}, which in this case consist of six critical points at the origin and one at both of {+1/2} and {-1/2}.)

Image

By choosing parameters appropriately, one can show that {X_1,\dots,X_5 = O(\sqrt{n})} and {\frac{1}{\pi} \int_{E_2(p)} |\psi|\ dA \leq 2n + O(1)}, yielding the first bound {\ell(\partial E_1(p)) \leq 2n + O(n^{1/2})}. However, by a more careful inspection of the arguments, and in particular measuring the defect in the triangle inequality

\displaystyle  |\psi(z)| = |\sum_\zeta \frac{1}{z-\zeta}| \leq \sum_\zeta \frac{1}{|z-\zeta|},

where {\zeta} ranges over critical points. From some elementary geometry, one can show that the more the critical points {\zeta} are dispersed away from each other (in an {\ell^1} sense), the more one can gain over the triangle inequality here; conversely, the {L^1} dispersion {\sum_\zeta |\zeta|} of the critical points (after normalizing so that these critical points have mean zero) can be used to improve the control on the error terms {X_1,\dots,X_5}. Optimizing this strategy leads to the second bound

\displaystyle \ell(\partial E_1(p)) \leq 2n + O(1).

At this point, the only remaining cases that need to be handled are the ones with bounded dispersion: {\sum_\zeta |\zeta| \leq 1}. In this case, one can do some elementary manipulations of the factorization

\displaystyle  p'(z) = n \prod_\zeta (z-\zeta)

to obtain some quite precise control on the asymptotics of {p(z)} and {p'(z)}; for instance, we will be able to obtain an approximation of the form

\displaystyle  p(z) \approx -1 + \frac{z p'(z)}{n}

with high accuracy, as long as {z} is not too close to the origin or to critical points. This, combined with direct arclength computations, can eventually lead to the third estimate

\displaystyle \ell(\partial E_1(p)) \leq 2n + 4 \log 2 + o(1).

The last remaining cases to handle are those of small dispersion, {\sum_\zeta |\zeta| = o(1)}. An extremely careful version of the previous analysis can now give an estimate of the shape

\displaystyle \ell(\partial E_1(p)) \leq \ell(\partial E_1(p_0)) - c \|p\| + o(\|p\|)

for an absolute constant {c>0}, where {\|p\|} is a measure of how close {p} is to {p_0} (it is equal to the dispersion {\sum_\zeta |\zeta|} plus an additional term {n |1 + p(0)|^{1/n}} to deal with the constant term {p(0)}). This establishes the final bound (for {n} large enough), and even shows that the only extremizer is {p_0} (up to translation and rotation symmetry).

Matthew Bolan, Joachim Breitner, Jose Brox, Nicholas Carlini, Mario Carneiro, Floris van Doorn, Martin Dvorak, Andrés Goens, Aaron Hill, Harald Husum, Hernán Ibarra Mejia, Zoltan Kocsis, Bruno Le Floch, Amir Livne Bar-on, Lorenzo Luccioli, Douglas McNeil, Alex Meiburg, Pietro Monticone, Pace P. Nielsen, Emmanuel Osalotioman Osazuwa, Giovanni Paolini, Marco Petracci, Bernhard Reinke, David Renshaw, Marcus Rossel, Cody Roux, Jérémy Scanvic, Shreyas Srinivas, Anand Rao Tadipatri, Vlad Tsyrklevich, Fernando Vaquerizo-Villar, Daniel Weber, Fan Zheng, and I have just uploaded to the arXiv our preprint The Equational Theories Project: Advancing Collaborative Mathematical Research at Scale. This is the final report for the Equational Theories Project, which was proposed in this blog post and also showcased in this subsequent blog post. The aim of this project was to see whether one could collaboratively achieve a large-scale systematic exploration of a mathematical space, which in this case was the implication graph between 4694 equational laws of magmas. A magma is a set {G} equipped with a binary operation {\diamond: G \times G \rightarrow G} (or, equivalently, a {G \times G} multiplication table). An equational law is an equation involving this operation and a number of indeterminate variables. Some examples of equational laws, together with the number that we assigned to that law, include

Up to relabeling and symmetry, there turn out to be 4694 equational laws that involve at most four invocations of the magma operation {\diamond}; one can explore them in our “Equation Explorer” tool.

The aim of the project was to work out which of these laws imply which others. For instance, all laws imply the trivial law {E1}, and conversely the singleton law {E2} implies all the others. On the other hand, the commutative law {E43} does not imply the associative law {E4512} (because there exist magmas that are commutative but not associative), nor is the converse true. All in all, there are {22,028,942} implications of this type to settle; most of these are relatively easy and could be resolved in a matter of minutes by an expert in college-level algebra, but prior to this project, it was impractical to actually do so in a manner that could be feasibly verified. Also, this problem is known to become undecidable for sufficiently long equational laws. Nevertheless, we were able to resolve all the implications informally after two months, and have them completely formalized in Lean after a further five months.

After a rather hectic setup process (documented in this personal log), progress came in various waves. Initially, huge swathes of implications could be resolved first by very simple-minded techniques, such as brute-force searching all small finite magmas to refute implications; then, automated theorem provers such as Vampire or Mace4 / Prover9 were deployed to handle a large fraction of the remainder. A few equations had existing literature that allowed for many implications involving them to be determined. This left a core of just under a thousand implications that did not fall to any of the “cheap” methods, and which occupied the bulk of the efforts of the project. As it turns out, all of the remaining implications were negative; the difficulty was to construct explicit magmas that obeyed one law but not another. To do this, we discovered a number of general constructions of magmas that were effective at this task. For instance:

  • Linear models, in which the carrier {G} was a (commutative or noncommutative) ring and the magma operation took the form {x \diamond y = ax + by} for some coefficients {a,b}, turned out to resolve many cases.
  • We discovered a new invariant of an equational law, which we call the “twisting semigroup” of that law, which also allowed us to construct further examples of magmas that obeyed one law {E} but not another {E'}, by starting with a base magma {M} that obeyed both laws, taking a Cartesian power {M^n} of that magma, and then “twisting” the magma operation by certain permutations of {\{1,\dots,n\}} designed to preserve {E} but not {E'}.
  • We developed a theory of “abelian magma extensions”, similar to the notion of an abelian extension of a group, which allowed us to flexibly build new magmas out of old ones in a manner controlled by a certain “magma cohomology group {H^1_E(G,M)}” which were tractable to compute, and again gave ways to construct magmas that obeyed one law {E} but not another {E'}.
  • Greedy methods, in which one fills out an infinite multiplication table in a greedy manner (somewhat akin to naively solving a Sudoku puzzle), subject to some rules designed to avoid collisions and maintain a law {E}, as well as some seed entries designed to enforce a counterexample to a separate law {E'}. Despite the apparent complexity of this method, it can be automated in a manner that allowed for many outstanding implications to be refuted.
  • Smarter ways to utilize automated theorem provers, such as strategically adding in additional axioms to the magma to help narrow the search space, were developed over the course of the project.

Even after applying all these general techniques, though, there were about a dozen particularly difficult implications that resisted even these more powerful methods. Several ad hoc constructions were needed in order to understand the behavior of magmas obeying such equations as E854, E906, E1323, E1516, and E1729, with the latter taking months of effort to finally solve and then formalize.

A variety of GUI interfaces were also developed to facilitate the collaboration (most notably the Equation Explorer tool mentioned above), and several side projects were also created within the project, such as the exploration of the implication graph when the magma was also restricted to be finite. In this case, we resolved all of the {22,028,942} implications except for one (and its dual):

Problem 1 Does the law {x = y \diamond (x \diamond ((y \diamond x) \diamond y))} (E677) imply the law {x = ((x \diamond x) \diamond x) \diamond x} (E255) for finite magmas?

See this blueprint page for some partial results on this problem, which we were unable to resolve even after months of effort.

Interestingly, modern AI tools did not play a major role in this project (but it was largely completed in 2024, before the most recent advanced models became available); while they could resolve many implications, the older “good old-fashioned AI” of automated theorem provers were far cheaper to run and already handled the overwhelming majority of the implications that the advanced AI tools could. But I could imagine that such tools would play a more prominent role in future similar projects.

Archives