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August 2025
Sun	Mon	Tue	Wed	Thu	Fri	Sat
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24	25	26	27	28	29	30
31

August 2025's Entries

Jack Morava
- Aug 2, 2025
- I hear that Jack Morava died on August 1, 2025.

Random Past Entries

TeXnical Issues
- September 2, 2006
- Sage advice on viewing this blog and posting comments thereon.
Probability in Amsterdam
- May 1, 2007
- Foundations of the Formal Sciences conference in Amsterdam.
Integral Octonions (Part 9)
- Nov 23, 2014
- Learn about using integral octonions and the E₈ lattice to construct the Leech lattice.
Large Sets 8
- Jul 2, 2021
- Some cardinal arithmetic.
Euler’s Continued Fraction Formula
- Aug 30, 2020
- A continued fraction for pi/4.
Research Fellowships in Representation Theory and/or Low Dimensional Topology at Leeds
- Jun 19, 2023
- Apply for a job in Leeds.

Recent Comments

Lawvere’s Work on Arms Control (11)
- Steve Huntsman
  - Jul 30, 2025 17:08
  - Barium meal test per Wikipedia
- Alex Shpilkin
  - Jul 30, 2025 13:25
  - The category Lawvere introduced in 1962 does indeed look the same as the one described by Chentsov (and presented by ...
- Steve Huntsman
  - Jul 30, 2025 13:02
  - In which wanting peace and thus preparing for war was so traumatic as to catalyze enthusiasm for the Great Leap ...
- Gavin Wraith
  - Jul 29, 2025 20:08
  - So many words enter the language as acronyms and thereafter different rules of capitalization apply. I am not sure whether ...
- John Baez
  - Jul 29, 2025 13:19
  - Thanks for telling us that! I was curious about the evolution of his attitude. So perhaps the RAND Corporation may ...

The Duflo Isomorphism and the Harmonic Oscillator Hamiltonian (6)
- Jacques Distler
  - Jul 29, 2025 13:20
  - I would argue (somewhat unconventionally) that the 12\tfrac{1}{2} is unnatural. Let’s generalize this slightly to nn identical harmonic oscillators. Passing ...
- John Baez
  - Jul 28, 2025 20:08
  - You’re right, I was wrong: the quantum harmonic oscillator Hamiltonian is not in the center of the universal enveloping algebra ...
- Peter Woit
  - Jul 28, 2025 19:21
  - Ignore my last comment, crossed yours. Will read your new Kepler problem post to see what you are really asking ...
- Peter Woit
  - Jul 28, 2025 19:17
  - Reading your question more carefully, I realize things to say are H isn’t in the center of the universal enveloping ...
- John Baez
  - Jul 28, 2025 19:06
  - I know how the extra 1/21/2 in the harmonic oscillator Hamiltonian is connected to the metaplectic group being a double ...

2-Rig Conjectures Proved? (5)
- John Baez
  - Jul 26, 2025 09:17
  - What we’re doing is sort of a categorification of that. A 2-rig contains some objects xx where the symmetry isomorphism ...
- John Baez
  - Jul 26, 2025 09:07
  - One way out, without changing any definitions, might be this: Show that Rep(M(n,k))\mathsf{Rep}(M(n,k)) is the free 2-rig on an object ...
- Jacques Distler
  - Jul 26, 2025 08:19
  - I know nothing about any of this. But in the more pedestrian world of ℤ 2\mathbb{Z}_2 graded-commutative algebras, there are ...
- John Baez
  - Jul 25, 2025 20:42
  - This is a great point. Unfortunately I have not yet carefully examined Coulembier’s paper, but now I have a great ...
- Mike Shulman
  - Jul 25, 2025 19:50
  - It’s curious to me to see something freely generated by something defined (partially) by a negative condition (an object has ...

The Clowder Project (3)
- Emily
  - Jul 25, 2025 19:39
  - Hey John, thanks again for the help with the post! I chose the name Clowder because it is the “collective ...
- Paolo Perrone
  - Jul 25, 2025 19:32
  - I suppose it’s as in “a clowder of cats”?
- John Baez
  - Jul 25, 2025 11:23
  - This is impressive—it’s already quite huge, and I hope more people join in. Here’s a dumb question: why “clowder”?

Tannaka Reconstruction and the Monoid of Matrices (14)
- John Baez
  - Jul 25, 2025 09:10
  - Kevin Coulombier has claimed a proof of the Conjecture described above—on the universal property of Rep(M(n,k))\mathsf{Rep}(\text{M}(n,k))—and also a new proof ...
- jack morava
  - Jun 8, 2025 14:58
  - I’ve been told that quasisymmetric functions are functions of countably many variables, almost all of which are zero. This has ...
- lambda
  - Jun 7, 2025 20:05
  - Doesn’t the character depend on which variable you set to 1? It doesn’t matter because they’re quasisymmetric. One way to ...
- John Baez
  - Jun 7, 2025 17:40
  - Thanks! That’s the best explanation of quasisymmetric functions that I’ve heard in my life. I will think about it. Then ...
- lambda
  - Jun 7, 2025 15:55
  - Quasisymmetric functions are categorified by representations of the 0-Hecke algebra, in the same way that symmetric functions are categorified by ...

How to Count n-Ary Trees (7)
- John Baez
  - Jul 25, 2025 08:34
  - I keep meaning to expand this article a bit so it shows how we get from the general formula for ...
- John Baez
  - Jul 8, 2025 18:40
  - I blogged about Aguilar and Ardila’s work here: More secrets of the associahedra, January 25, 2018. But now I am ...
- Kenneth
  - Jul 8, 2025 18:32
  - Here is perhaps one way to interpret Lagrange inversion from a different (deeper?) perspective, namely generalized permutahedra: Marcelo Aguiar and ...
- Tom Copeland
  - Jul 8, 2025 00:06
  - Should the reciprocity for the rising and falling factorials (−nk)=(−1) k(n+k−1k) \binom{-n}{k} = (-1)^k \binom{n+k-1}{k} arise in your machinations and/or ...
- Tom Copeland
  - Jul 7, 2025 21:39
  - The classic Lagrange inversion partition polynomials, giving the inverse of formal Taylor series, or exponential generating functions, are presented in ...

Comagnitude 1 (26)
- Tom Leinster
  - Jul 15, 2025 17:38
  - There’s a typo on the slide with the PDE on it, which I can’t fix just now. Where I’ve written ...
- John Baez
  - Jul 13, 2025 09:50
  - Cool! Good luck!
- Tom Leinster
  - Jul 13, 2025 09:36
  - I’m going to be speaking about this stuff at Category Theory 2025 next week. My talk is almost exclusively about ...
- Tom Leinster
  - Feb 25, 2025 20:20
  - That challenge of Terry’s is a great one! I think about it every now and then. But I haven’t thought ...
- David Corfield
  - Feb 15, 2025 12:54
  - Is a Categorified Two Cultures Challenge on the cards? For X,Y:A→FinSetX, Y: A \to FinSet, and FF a natural transformation ...

Counting with Categories (Part 3) (5)
- John Baez
  - Jul 2, 2025 18:39
  - Looking a bit more at the paper we’re talking about Marcelo Aguiar, Federico Ardila, Hopf monoids and generalized permutahedra. it’s ...
- John Baez
  - Jul 2, 2025 15:31
  - Good questions! I don’t really understand that formula for the compositional inverse of a formal power series in terms of ...
- Allen Knutson
  - Jul 2, 2025 15:23
  - Where does the tree-like structure story relate to Lagrange inversion, as in More secrets of the associahedra? Maybe I’m asking ...
- John Baez
  - Jul 2, 2025 05:59
  - When I first met James online on sci.math, he always typed in all caps. I eventually told him that made ...
- Allen Knutson
  - Jul 2, 2025 05:30
  - james dolan should complain that you misspelled generatingfunctionology as Generatingfunctionology. Say a species S has a generating function g, and ...

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August 2, 2025

Jack Morava

Posted by John Baez

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

Today I heard from David Benson that Jack Morava died yesterday. This comes as such a huge shock that I can’t help but hope Benson was somehow misinformed. Morava has been posting comments to the n-Café and sending emails to me even very recently.

This is all I know, now.

Posted at 12:22 PM UTC | Permalink | Post a Comment

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