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February 2025's Entries

Backing Up US Federal Databases
- Feb 2, 2025
- If you want to help save US federal web pages and databases, here are some things to do.

Random Past Entries

TeXnical Issues
- September 2, 2006
- Sage advice on viewing this blog and posting comments thereon.
Inner Automorphisms of the Octonions
- Nov 22, 2022
- Apparently there are some nontrivial inner automorphisms of the octonions.
Group Cohomology and Homotopy Fixed Points
- Apr 28, 2020
- An explanation of crossed homomorphisms, leading up to a sketch proof of Hilbert’s Theorem 90.
Causality in Machine Learning
- Nov 8, 2021
- Introducing causality into machine learning
Arithmetic Gauge Theory
- Dec 21, 2017
- Arithmetic gauge theory
Jordan Algebras
- Jun 7, 2020
- What’s the conceptual meaning of the Jordan algebra axioms?

Recent Comments

The Dual Concept of Injection (17)
- Tom Leinster
  - Feb 3, 2025 11:53
  - Do the Dirichlet binomial coefficients have lots of nice algebraic properties, like the ordinary binomial coefficients?
- John Baez
  - Feb 1, 2025 18:43
  - The concept dual to injection, or more precisely the concept dual to taking a set SS and decomposing it as ...
- Tom Leinster
  - Jan 23, 2025 18:52
  - And a dual result holds too! In other words, for a finite acyclic quiver QQ, we can easily describe which ...
- Tom Leinster
  - Jan 23, 2025 14:49
  - I sat down and checked, and as I’d hoped, an exact analogue of the result you mention holds in the ...
- Tom Leinster
  - Jan 22, 2025 13:08
  - Excellent; thanks very much. That’s exactly the kind of thing I was hoping for, but I wouldn’t have known where ...

Comagnitude 1 (20)
- Sofia B
  - Feb 2, 2025 16:48
  - Regarding your formula for the discrepancy of the pushout, I’m reminded of the formula P(a∨b)+P(a∧b)=P(a)+P(b)P(a \vee b) + P(a \wedge ...
- Tom Leinster
  - Jan 29, 2025 08:25
  - Thanks for the ideas! It’s entirely possible I’ve overlooked something straightforward, but I don’t think I’ve omitted any assumptions. A ...
- product action
  - Jan 28, 2025 21:43
  - Did you maybe omit some assumptions in what you stated? I mean the idea I suggested does define an action ...
- Mike Shulman
  - Jan 28, 2025 08:53
  - That’s nicely explained, thanks. We didn’t actually say anything about Grothendieck constructions in our paper, because we were focused more ...
- product action
  - Jan 27, 2025 12:49
  - Thank you for your patience! One could try to construct an action of End I(A)×End J(A)End_{I}(A) \times End_{J}(A) on End ...

Comagnitude 2 (4)
- John Baez
  - Feb 1, 2025 18:03
  - Lior Yanovski told me that Berman himself informed him that Berman’s paper has a mistake, which is why it was ...
- Mike Shulman
  - Feb 1, 2025 16:08
  - Also, Lior Yanovski’s paper Homotopy Cardinality via Extrapolation of Morava-Euler Characteristics (2303.02603) has a related abstract: We answer a question ...
- Tom Leinster
  - Feb 1, 2025 09:01
  - Right, I should have emphasized those dualities that you emphasized! One piece of progress on homotopy cardinality that’s been made ...
- Mike Shulman
  - Feb 1, 2025 06:32
  - This is really interesting! I’m sure you know this, but I thought I would point out that althought the free ...

Random Permutations (Part 14) (23)
- Korepetytor Matematyki
  - Jan 22, 2025 19:54
  - Blog that draws the reader into the world of mathematical structures and their subtle properties. With elegance and precision, the ...
- Tom Leinster
  - Dec 21, 2024 23:16
  - I’m not sure it is either! In situations like this, I like to ask myself whether a proof could be ...
- John Baez
  - Dec 21, 2024 20:29
  - Nice! I’m not sure the relation “P instantly follows from Q” is transitive, but I will accept this as a ...
- Tom Leinster
  - Dec 21, 2024 17:07
  - John wrote: Corollary. Given a random permutation of an nn-element set, the expected number of points lying on kk-cycles is ...
- John Baez
  - Dec 21, 2024 01:40
  - I’ve polished up this blog article and turned it into a paper: Groupoid cardinality and random permutations. It’s the shortest ...

Martianus Capella (15)
- Mozibur Rahman Ullah
  - Jan 16, 2025 04:30
  - The Oxford calculators were mostly based at Merton college from what I can recall. Interestingly, they proved a mean speed ...
- Thomas
  - Jan 11, 2025 00:08
  - John’s description of the “Oxford Calculators” on Azimuth shows how interesting things can come from small groups which just vanish. ...
- Mozibur Rahman Ullah
  - Jan 7, 2025 13:37
  - I’ve dipped into Russo’s book but I found it a bit dry. I might give it another go. His theory ...
- John Baez
  - Jan 4, 2025 01:50
  - Lucio Rosso’s book is definitely worth reading! You don’t have to believe his whole hypothesis to enjoy reading about what ...
- Thomas
  - Jan 3, 2025 14:42
  - That only so few of the ancient texts survived caused speculations about a maybe forgotten revolution in analogy to the ...

Axiomatic Set Theory 2: The Axioms, Part One (17)
- Bowen
  - Jan 14, 2025 01:09
  - Hi, Prof. Leinster, Thanks for your reply. I can understand them now. I really enjoy this lecture notes, the proofs ...
- Tom Leinster
  - Jan 13, 2025 11:48
  - Hi! Hope you’re enjoying the notes. Yes, equality between functions (with the same domain and same codomain) is taken as ...
- Bowen
  - Jan 13, 2025 01:49
  - Also, it seems that you didn’t explicitly show that the existence of identity functions for every set, while in the ...
- Bowen
  - Jan 13, 2025 01:37
  - Hi, Prof. Leinster, I am reading the Chapter 2 of your lecture notes and I have question on axiom 1. ...
- David Roberts
  - Sep 30, 2024 07:51
  - Another thing to note for people ok with categories: assume we have the category Set, and are trying to instead ...

Wormholes and Entanglement (45)
- John Baez
  - Jan 7, 2025 07:11
  - Thanks for the heads-up! I’ll have to try reading this paper by Witten sometime.
- Blake Stacey
  - Jan 7, 2025 04:30
  - Chiming in many turbulent years later to note that Witten has suggested that in the presence of gravity, the algebra ...
- Jamie Vicary
  - Oct 24, 2014 16:55
  - You’re asking great questions about making my ‘sensors’ idea more precise. I haven’t really thought it through to the level ...
- Howard Barnum
  - Oct 23, 2014 21:31
  - Just correcting the spelling of the link associated with my name (i.e., to my website).
- Howard Barnum
  - Oct 17, 2014 18:59
  - Great question, Tobias; great answers, Jamie (and John, earlier). I have been wondering the same thing, on and off, about ...

Every Functor is a (Co)Reflection (2)
- Julius
  - Jan 3, 2025 14:22
  - Typo: “However, it is true that every functor can be made into a (co)relection by changing its domain.” -> “However, ...
- Tom Leinster
  - Sep 10, 2012 07:04
  - I don’t have another example to offer, but I do have what might be the seed of an idea. By ...

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February 2, 2025

Backing Up US Federal Databases

Posted by John Baez

$MathML-enabled post (click for more details).$

I hope you’ve read the news:

Ethan Singer, Thousands of U.S. government web pages have been taken down since Friday, New York Times, 2 Feburary 2025.

Many of the pages taken down mention DEI, but they also include research papers on optics, chemistry, medicine and much more. They may reappear, but at this time nobody knows.

If you want to help save US federal web pages and databases, here are some things to do.

Continue reading “Backing Up US Federal Databases” …

Posted at 11:40 PM UTC | Permalink | Post a Comment