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lieven lebruyn
mathematician by day, blogger by night
mathematician by day, blogger by night

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The nicest summary of today's evens is probably this tweet by +Emily Riehl

"Ageism is real (as is aging). It's shortsighted to respond with anything other than empathy. This is what I imagine for my future, should I be so lucky to still be here to live it:

"Let X equal the quantity of all quantities of X. Let X equal the cold...""

The quote comes, of course, from "Proof"

(1.26 into clip)
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after the #ABC, #IUTeich and #Mochizuki era, soon #RH and #Atiyah will be trending.
Monday september 25th Atiyah will present his proof of the Riemann hypothesis (at the Heidelberg laureate forum).
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2^77232917 - 1 is prime

It was discovered on December 26, 2017 by Jonathan Pace, and verified to be a prime by GIMPS using four different programs on four different hardware configurations.
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We're heading for a bad ending

Yesterday, my feeds became congested by (Japanese) news saying that Mochizuki's (claimed) proof of the abc-conjecture had been vetted and considered fit to be published in a respectable journal.

Today, long term supporters of M's case began their Echternachian-retreat after finding out that Mochizuki himself is the editor in charge of that respectable journal.

Attached is Ed Frenkel's retraction of his previous tweet. Also, Taylor Dupuy deemed the latest action a bridge too far:

Peter Woit did a great job in his recent post
pinpointing a critical argument in the 500-page long papers having as its "proof" that it followed trivially from the definitions...

I'd expect any board of editors to resign in such a case.
I fear this can only end badly.

#Mochizuki, #IUTT, #ABC-conjecture
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le Tour de France in Grothendieck's backyard

If you want to see the scenery Grothendieck enjoyed in his later years, watch the Tour de France tomorrow.
It starts in Saint-Girons where he went to the weekly market [0] (and died in hospital, november 13th 2014), ending in Foix with 3 category 1 climbs along the way (familiar to anyone familiar with Julia Stagg's expat-lit set at 'Fogas' [1],[2]).
It will not pass through Lasserre [3] (where G spend the final 20 years of his life) which is just to the north of Saint-Girons.

#Grothendieck #Ariege #France

[0] :
[1] :
[2] :
[3] :
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Buy a Grothendieck painting to get the Lasserre notes online!

As of yesterday, most of Grothendieck's Montpellier notes are freely available at
There's much to say about the presentation (eg. It is not possible to link directly to a given page/article, it is scanned at only 400 dpi etc. etc.) but hey, here they are at last, for everyone to study.
By far the most colourful (in my first browsing of the archive) is cote No. 154, on 'systeme de pseudo-droites'. You can download it in full (a mere 173 Mb).
As you know, the Montpellier notes are only a fraction of the material Grothendieck left behind. By far the largest (though probably not the most interesting, mathematically) are the Lasserre notes, which to the best of my knowledge are in the care of a Parisian bookseller.
Here's an idea:
almost every page of No. 154 (written on ancient computer-output) looks like a painting. No doubt, most math departments in the world would love to acquire one framed page of it. Perhaps this can raise enough money to safeguard the Lasserre notes...

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For all of you waiting for Grothendieck's Montpellier notes to be released tomorrow, the address is as of 18.00 GMT May 10th:

I've just received the following mail:

Chères toutes et tous,

J’ai le plaisir de vous annoncer qu’après des mois de négociations, nous allons être en mesure de diffuser une partie significative (18000 pages / 28000) du fonds d’archives Alexander Grothendieck de Montpellier. Une cérémonie / conférence de presse est prévue demain (mercredi 10 mai) en fin d’après-midi à l’Université de Montpellier.

L’adresse du site dédié est la suivante:

Pour l’instant l'accès est bloqué par un mot de passe, les 18000 pages seront consultables et téléchargeables librement dès demain 18h.

N’hésitez pas à communiquer cette information aux membres de vos laboratoires.

Bien amicalement,

Jean-Michel Marin
Directeur de l’Institut Montpelliérain Alexander Grothendieck
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Grothendieck's Montpellier notes will hit the net May 10th

At last there is an agreement between the university at Montpellier and Grothendieck's children to release the 'Montpellier gribouillis' (about 28000 pages will hit the net soon).
Another 65000 pages, found at Lasserre after Grothendieck's death, might one day end up at the IHES or the Bibliotheque Nationale.
If you are interested in the history of Grothendieck's notes, there is this old post on my blog:

(h/t Theo Raedschelders for the Liberation link)
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Nice Quanta-article on the cosmic Galois group.

Here's the arXiv paper by Francis Brown on which it is based:
Here's some info about the cosmic group at the nLab:
And an older arXiv note by Jack Morava:

Quanta: "Brown is looking to prove that there’s a kind of mathematical group — a Galois group — acting on the set of periods that come from Feynman diagrams. “The answer seems to be yes in every single case that’s ever been computed,” he said, but proof that the relationship holds categorically is still in the distance. “If it were true that there were a group acting on the numbers coming from physics, that means you’re finding a huge class of symmetries,” Brown said. “If that’s true, then the next step is to ask why there’s this big symmetry group and what possible physics meaning could it have.”

Among other things, it would deepen the already provocative relationship between fundamental geometric constructions from two very different contexts: motives, the objects that mathematicians devised 50 years ago to understand the solutions to polynomial equations, and Feynman diagrams, the schematic representation of how particle collisions play out. Every Feynman diagram has a motive attached to it, but what exactly the structure of a motive is saying about the structure of its related diagram remains anyone’s guess."
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