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New math book rescues landmark topology proof

quantamagazine.org

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Re: New math book rescues landmark topology proof

#101
post #92

Earlier quoted context omitted.

Thanks for response! I will definitely read about Turing jumps :) I'm not sure I understand your 1. Reading the Halting problem undecidability proof, it goes like this: Suppose machine H can solve the halting problem. We construct special machine M which calls H(M), and negates the output. Then when we run H(M), it halts if M doesn't halt, and doesn't halt if M halts, hence M doesn't exist. On the other hand, if H co…

How do you generate the sequence H_0, H_1, ...? Specifically, is there a Turing machine G that can generate H_0, H_1, ..., onwards, perhaps taking in some input along the way? If so, then you can construct a self-contained Turing machine Z that takes a machine M as input, which works as follows: it calls G to generate H_0, runs H_0 for a bit on M, then calls G to generate H_1, runs H_1 for a bit on M, and so forth. T…

Thanks so much! This is fun.

I think, with your explanation, there's still a big handicap for the halting machine code.

To illustrate.. If I were to say to you: Is the correct answer yes or no, considering that later I will reverse my answer, and enforcing that you can't later change your answer? It's like, okay, of course, with that model, you can never win. I don't think it reveals any limitation of your understanding, you just got pulled into a game that you can't win.

The limitation that is put on the code and in your example too is, although the machine can take in extra input along the way, at a certain point the mathematician gets the last word.

If you have G(H,M) which at each point gives you [0|1]:H', a more interesting question is if what happens if you define M = "if H(M)[0]: print H(M)[1] and then loop". Then, does the printed out H(M)[1](M) produce any contradiction?

Hopefully I'm making sense here! Thanks again for engaging.

Re: New math book rescues landmark topology proof

#102

If I understand this article, it’s about a 500-page book that is devoted to one proof of one theorem in topology. I find that amazing. And cheers to Quantum Magazine for regularly publishing popularizations of research mathematics. I know many, at times, take issue with their simplifications and framing, but they’re trying, where almost no one else with their reach covers these areas at all.

I wonder how many other results in maths require an entire book length treatment (or multiple book length treatments)? The one that jumps out to my mind is Gödel's Incompleteness Theorem(s)[1]. I know there are at least a couple of complete books dealing exclusively with this result. [1]: https://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_...

I did a University module on Godel' Incompleteness theotem and the complete lecture notes which gave all the lead up, explanation and the proof itself along with lots of othet related material was only about 50 pages in total if I recall correctly.

Was a pleasure to do that module though!

Re: New math book rescues landmark topology proof

#103

Earlier quoted context omitted.

I suspect someone could write a book (or an HN comment at least) about the popular confusion about Godel's 1st incompleteness theorem. :-) In fact we (my brother and I) agreed that it bears a striking resemblance to Turing's halting problem: They both seem to show what computers or math can't do, but in fact both theorems only reveal limitations of certain models of computers and/or math. We both have undergrad degre…

I found this nice presentation about Godel's theorems. https://youtu.be/HeQX2HjkcNo?t=895 "There is no proof for the statement with Godel-number g". What I'm struggling with is trying to understand if self-reference can be formally represented by some symbol. Can it? Godel's proof seems to rely on a trick that allows a formal system to talk about itself but is that possible? There would need to be a symbol for that a…

Not every picture of a pipe is a pipe but it's at least conceivable that an actual working pipe can be constructed out of something which happens to be a picture of a pipe. Similarly Godel isn't proving that all statements in a system are paradoxically self-referential. Only that given any system of sufficient complexity, one can conceivably be constructed.

In any event, all of our mathematical proofs are predicated upon the idea that the representation of a mathematical object can be treated in terms of proof as equivalent to the mathematical object. Is "2" the number 2 or is it just a glyph that non-representationally depicts the successor of the first counting number? And if you believe the latter, then how do you go about proving anything about the actual successor of the first counting number without resorting to glyphs?

Re: New math book rescues landmark topology proof

#104

Earlier quoted context omitted.

There is a language called lean which is popular among mathematicians. Here is an article: https://www.quantamagazine.org/building-the-mathematical-lib... A more recent article as well: https://www.quantamagazine.org/lean-computer-program-confirm...

My question was specifically referring to these huge 500 proofs that only a handful of people have even attempted to understand. What is the upper limit of what our current state-of-the-art proof assistants can handle?

The problem is not the limit of what proof checkers can handle - that probably goes beyond all known math. The problem is that long standing theories that 500 page proof is based on are not yet transcribed into formal language, so you'd need to do them first.

Re: New math book rescues landmark topology proof

#105

I really wish I could get math to stick. I just finished my National 5 maths (rough equivalent of a US High School Diploma) night-class today and all I ever seem to understand is how, but not why. I'm the one asking "why is that that." And today was recapping on trinomial, simplifying fractions. Simple I expect to anyone with a mathematical mind, but to me, it's just an insane implosion which leaves me exhausted. I h…

You need to transition to learning math.

One possible starting point is Book of Proof by Richard Hammach[0]. It's free. It will show you the rudiments of how math is actually done and thought of. Another good choice is Mathematical Proofs: A Transition to Advanced Mathematics by Chartrand/Polimeni/Zhang. These books have no prerequisites(good to go if you know how to do arithmetic with fractions/decimals; not that these are strictly necessary, rather that's about the level of comfort with math one should posses). Search on Amazon and you'll see there are a ridiculous number of books on this subject of all varieties of ways of presentation. Almost every week a new book pops up, it seems. Note, intro-to-proofs books are not only for novices, though. There are kinds written for advanced undergrads and beginning grad students as well. For example: Mathematical Concepts by Jugen Jost. This speaks to the wealth of the kinds of math books available.

Concurrently and/or after that you can study introduction to any of linear algebra, discrete math, group theory, analysis of reals, combinatorics, number theory, graph theory, algorithms, probability, category theory...whatever. Each of these are very deep subjects and there exist hundreds(if not 1000s of books from the past, current and future) of every imaginable level, depth and presentational quirk. Again check Amazon for titles. Check libge*n for actual files.

The following intro books are so easy anyone and they momma can read these with utmost ease:

Discrete Math by Susanna Epp

How to Think about Analysis by Lara Alcock

Linear Algebra: Step by Step by Kuldeep Singh

Real Analysis: A Long-Form Mathematics Textbook by Jay Cummings

A Tour Through Graph Theory by Karin Saoub

The above mentioned books are a few examples of elementary books that you can get started with right this minute.

Note and remember the wealth of possible books, though. For example, consider the subject of math analysis.

We can break it into three general parts: real analysis, complex analysis, functional analysis. Each can be further taken apart into measure theory, vector spaces, topology etc. Further, topology alone branches out into point-set topology, algebraic topology, differential topology etc. Each of these fly under many different names. Say, vector spaces is a huge part of linear algebra. For the beginners, it's usually the finite dimensional vector spaces (aka the title of a famous linear algebra book) version whereas the infinite version will take you into func analysis. Vector spaces are also usually included as a chapter in books on abstract algebra as they are an algebraic structure just like groups, rings, modules. But if there is linear algebra, there must be non-linear algebra too. Well, yes. Roughly, it corresponds to what's called algebraic geometry. It never ends.

The point is every topic in math has loads of books dedicated to it. In turn every topic has a (sub)^{n}topic and there are tons of books on those. Each of the books come in elementary, quirky, armchair enthusiast, average undegrad student, middling grad student, kickazz graduate math aficionado, researcher, undergrad researcher wanna-be etc levels. There are also olden books, classics, those just published (say, at most 5 years ago) and up-and-coming ones. Also, each term in math has bagillion synonyms. So multiply the number of books above by n. I am not even gonna mention books written in different languages and lecture notes that are available for free online. A lot of published book often spend years as a free set of lecture notes before ending up on Amazon as a newly published book. There are also Olympiad books, proof compilations, capstone compilations, intro-to-research books, those that prove a single theorem and in the process go through tons of disparate math etc Take advantage of all of this.

[0] https://www.people.vcu.edu/~rhammack/BookOfProof/

Re: New math book rescues landmark topology proof

#106
post #74

I do find it amazing that mathematicians seem to have almost infinite time to work on problems, and so much freedom to choose what they're working on. How great that a big group of people can collectively decide to spend years creating a book like this.

What is amazing to me is that most people think they do not have such freedom.

Most people don’t as doing so requires a level of talent, intelligence, and work ethic/determination that’s in the upper tail of human distribution.

Paradoxically, many people who could probably do underestimate their talents while others who can’t/should t overestimate theirs. The universe is funny in that way.

Re: New math book rescues landmark topology proof

#107

If I understand this article, it’s about a 500-page book that is devoted to one proof of one theorem in topology. I find that amazing. And cheers to Quantum Magazine for regularly publishing popularizations of research mathematics. I know many, at times, take issue with their simplifications and framing, but they’re trying, where almost no one else with their reach covers these areas at all.

I wonder how many other results in maths require an entire book length treatment (or multiple book length treatments)? The one that jumps out to my mind is Gödel's Incompleteness Theorem(s)[1]. I know there are at least a couple of complete books dealing exclusively with this result. [1]: https://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_...

The incompleteness theorem can be proved in a few lines given the right definitions up front. It's basically the same as the undecidability of the halting problem, which has a proof that is written as a poem: https://introcs.cs.princeton.edu/java/54computability/haltin...

There is a wonderful book by Torkel Franzén about the incompleteness theorem that is 100+ pages, but it is not purely about the proof. It's a popularization that discusses bogus ways philosophers have interpreted the theorem, and stuff like that. It is called "Gödel's Theorem: An Incomplete Guide to its Use and Abuse".

Meanwhile Aschbacher and Smith's proof of the classification of quasithin groups really is a book of 1200+ pages: https://books.google.com/books?id=SbO2irSQHMEC

And of course the proof of the classification of finite simple groups has afaik never been published all in one place, though there are some book-length expositions of it referring back to the original papers. It is a set of papers spanning around 20 years and adding up to around 10,000 pages. It is sometimes called "the enormous theorem": https://en.wikipedia.org/wiki/Enormous_theorem

Re: New math book rescues landmark topology proof

#108

Earlier quoted context omitted.

I wonder how many other results in maths require an entire book length treatment (or multiple book length treatments)? The one that jumps out to my mind is Gödel's Incompleteness Theorem(s)[1]. I know there are at least a couple of complete books dealing exclusively with this result. [1]: https://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_...

I suspect someone could write a book (or an HN comment at least) about the popular confusion about Godel's 1st incompleteness theorem. :-) In fact we (my brother and I) agreed that it bears a striking resemblance to Turing's halting problem: They both seem to show what computers or math can't do, but in fact both theorems only reveal limitations of certain models of computers and/or math. We both have undergrad degre…

> I suspect someone could write a book (or an HN comment at least) about the popular confusion about Godel's 1st incompleteness theorem. :-)

That book has already been written: https://www.ams.org/notices/200703/rev-raatikainen.pdf

Re: New math book rescues landmark topology proof

#109

So who gets credit for proving it? Freedman, the original author from 1981; or the authors of this book? If Freedman's proof has so many gaps, should it be considered more of a proof outline, or a motivation for believing a conjecture, and the current book be considered the actual proof? Or does Freedman get the glory? In that case, there's not much incentive for people to do what these book authors did. Which I supp…

It's common for complicated proofs to have little gaps that got past the referees. The basic standard of whether the proof is valid is that if you do find a gap in the written version, the author can say "oh yeah, you can fix that by doing X", making some small patch. It's like finding a bug in a program that the author can fix right away once you file a bug report. If the author is unable to fix the bug despite a reasonable amount of effort, then there is a problem. You get credit if you can fix it where the author couldn't. Otherwise it's almost like trying to invalidate a proof over a misspelling.

In the case of Wiles' proof of FLT, someone found a bug, Wiles worked unsuccessfully for something like a year trying to fix it, basically concluded that FLT was not really completely proved after all (i.e. he had "merely" made enormous progress, but not actually closed the ticket). Then right after more or less giving up, he and Richard Taylor figured out how to fix the bug, so it came out ok after all. Of course Taylor now gets a slice of the FLT credit.

Re: New math book rescues landmark topology proof

#110
post #44

Earlier quoted context omitted.

> mathematics is not plagued with false "theorems." But you don't know that. There certainly were precedents: https://mathoverflow.net/questions/291158/proofs-shown-to-be...

The answer given there by Manuel Eberl is more or less what I was trying to get at (and he is far more knowledgeable about it than I am). Lots of mathematicians find that the existing level of rigor in the field is enough. Obviously the people who like proof assistants disagree, and they may be right. It could be that modern theorems are just too complicated to be adequately evaluated by unassisted humans. But mathem…

This is largely because in modern mathematics, people ignore or won't build on proofs that are too complicated for them to follow, and rely heavily on trust and networking effects for the remaining proofs that are too useful to ignore. Plenty of results (including big results) are published in mathematical journals each year, which are "known" to be flawed or sketchy, but never have a formal rebuttal, and if you want to build on a proof that doesn't have much followup work, and are having trouble understanding its argument, you're expected to ask around and find out whether the proof is worth pursuing or not. Proof assistants would enable people to trust much more complex proofs from much more junior mathematicians, rather than essentially requiring the community to reprove the same results over and over until they're satisfied, and IMO this is holding back mathematics more than many mathematicians realize.
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