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lieven lebruyn
Works at University of Antwerp
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Lives in Antwerp,Belgium
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lieven lebruyn

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wOZ declares 2015 mathematically sound!

“2015 is mathematically sound.
20 is 4*5 and 15 is 3*5. 2015 is 5*13*31. 13 and 31 are reversed digit prime numbers.
In binary 2015 is 11111011111, a palindrome.
2015 is also 3737 in base 8 (octal) and 37 is the most special number of all in my opinion. For one thing, it’s the best age. For another, it’s the first irregular prime number!"

a math-happy 2015 :: lieven.
Woz wishes us all a 'mathematically sound' New Year
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The 'avis de décès' released by Grothendieck's family and friends, published in the local French newspaper 'La Depeche', on saturday november 15th.

It announces Grothendieck's cremation, on november 17th at 11.30h in the village of Pamiers, bordering the 'Camp du Vernet', where Grothendieck's father Sasha was imprisoned, before being deported to Auschwitz and murdered by the Nazis in 1942. 
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Please keep an eye on the GrothendieckCircle for updates

+Leila Schneps invested a lot of time over the years setting up the Grothendieck Circle website

Some material had to be removed a few years ago as per Groth's request.

I'm sure many of you will be as thrilled as I was to get this message from Leila:

"I have already started modifying the Grothendieck circle website and it will of course eventually return completely.  Plus many things will be added, as we will now have access to Grothendieck's correspondence and many other papers."

Leila already began to update the site, for example there's this new page on Groth's life in Lasserre:

I understand Leila is traveling to Lasserre tomorrow, presumably for Grothendieck's funeral. Hopefully she will eventually post something about it on the GrothendieckCircle (or, why not here on G+).

The village of Lasserre - 200 residents - where Grothendieck lived as a recluse for over 23 years. The house where he lived. He took loving care of the plants and flowers, bringing shoots indoors to nourish them in individual pots. He made soup from his dandelions and once, long ago, ...
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+Felipe Voloch : settled now. perhaps they took the site offline over the weekend to update some pages. The Lasserre-page sure has been updated.
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Grothendieck's last hideout

The past ten days I've been up in the French mountains (without internet access), not that far from the Ariege, so I'm just now catching up with all (blog)posts related to Grothendieck's death.
At our place, the morning of thursday november 13th was glorious!
Even though FranceInter kept telling horror stories about flooding in more southern departements, I can only hope that Grothendieck passed away in that morning sun.
About a year ago, on the occasion of Groth's 85th birthday, I ran a series of posts on places where he used to live, ending with his last known hideout:
At the time I didn't include the precise location of his house, but now that pictures of it are in the French press I feel free to suggest (if you are interested to know where Grothendieck spend his later years) to point your Google-earth or Google-maps (in streetview!) to:
lat 43.068254  lon 1.169080
Certains le considèrent comme «le plus grand mathématicien du XXe siècle». Alexandre Grothendieck est décédé jeudi. Il s'était installé à Lasserre pour s'isoler. Les habitants connaissaient l'existence de cet homme discret, sans le fréquenter. ...
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lieven lebruyn

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For the few persisting  #Mochizuki  watchers: there's some activity at the twitter feed
Chung Pang Mok is touring Universities with an "introductory" talk to IUTeich. he's scheduled at University of British Columbia, Duke, UCSC, MSRI, possibly others.
If someone attended and saw a glimpse of light towards the end of the tunnel, please share!
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Grothendieck's café

“A story says that in a Paris café around 1955 Grothendieck asked his friends “what is a scheme?”. At the time only an undefined idea of “schéma” was current in Paris, meaning more or less whatever would improve on Weil’s foundations.” (Colin McLarty)

Finding that particular café in Paris, presumably in the 5th arrondissement, seemed like looking for a needle in a haystack. Until now.
There's this riddle in Bourbaki’s death announcement: "A reception will be held at the Bar ‘The Direct Products’, at the crossroads of the Projective Resolutions (formerly Koszul square)", and I'm pretty certain that Bar is none other than Roubaud's Café Plantin on the crossroads of rue Lhomond and rue d'Ulm.

From the correspondence between Serre and Grothendieck it is also possible to date the "What is a scheme?" story.

It happened on monday december 12th 1955 and it was Pierre Cartier who was able to answer Grothendieck's question.

Full details on my blog:

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hello! Support us we are new Belgian Invention! 
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lieven lebruyn

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the state of European mathematics in 1927

This map, from the Rockefeller foundation, gives us the top 3 mathematical institutes in 1927 : Goettingen, Paris and ... Rome.
The pie-charts per university show that algebra was a marginal topic then (wondering how a similar map might look today).

More details, including a link to the map of US-mathematics 1927, can be found on my new blog:
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+lieven lebruyn still, this ( did not appear out of a void. E.g. Łukasiewicz (of "Polish notation" fame) was already very well-known. Reminds me of modern "university rankings" stupidity a quite bit :-)
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Have him in circles
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Mochizuki in denial

From M's 2014 IUTeich-Progress-Report (17 pages, the 2013-edition was only 7 pages long):

"Activities surrounding IUTeich appears to be in a stage of transition from a focus on verification to a focus on dissemination."

If only... 

He further lists hypotheses as to why nobody (apart from his 3 disciples Yamashita,Saidi and Hoshi) makes a serious effort to  "study the theory carefully and systematically from the beginning":

1. it is too long (1500-2500 pages)
2. there's lack of textbooks on anabelian geometry
3. we are obsessed with the Langlands program
4. there's little room for generalisations
5. it may not be directly useful for our own research

But then, why should anyone make such an effort, as:

"With the exception of the handful of researchers already involved in the verification activities concerning IUTeich, every researcher in arithmetic geometry throughout the world is a complete novice with respect to the mathematics surrounding IUTeich, and hence, in particular, is simply not qualified to issue a definite judgment concerning the validity of IUTeich on the basis of a 'deep understanding' arising from his/her previous research achievements."

No Mochizuki, the next phase will not be dissemination, it will be denial.

Other remarkable sentences are:

"IUTeich is 'the correct theory' in the sense that it leads one to doubt the existence of any sort of 'alternative proof', i.e. via essentially different techniques, of the ABC Conjecture."


"the status of IUTeich in the field of arithmetic geometry constitutes a sort of faithful miniature model of the status of pure mathematics in human society."

Already looking forward to the 2015 'progress' report...


#Mochizuki, #IUTeich  
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+john iskra​ I would say that Lieven did some work to illuminate the concept of Frobenioid, with the view to IUTT, rather that the IUTT itself (and by his own admission, if I recall correctly). Minyong's MO postings are the only 'independent' exposition of the ideas M uses that I know of.
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#Grothendieck   #Bourbaki  
Nicolas Bourbaki is temporarily resurrected to announce the death of Grothendieck in the French newspaper Le Monde.
You may recall that Bourbaki passed away on november 11th 1968, see +Peter Luschny's post on his death announcement here :
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Mormoiron and Lasserre acknowledge Grothendieck

In the series of post on Grothendieck-places I wrote a year ago (see and links at the end) I tried to convince these French villages to update their Wikipedia page to acknowledge the existence of Grothendieck under the heading 'Personnalités liées à la commune', without much success.

Today it is nice to see that Lasserre added Grothendieck to their page ( :
"Alexandre Grothendieck (1928-2014), considéré comme un des plus grands mathématiciens du xxe siècle, y a vécu en quasi-ermite de 1990 à sa mort."

Also Mormoiron, where Grothendieck lived in the 80ties (see picture below) has updated its page (
"Alexandre Grothendieck a habité temporairement à Mormoiron ("Les Aumettes")"

French villages who still have to follow suit:
- Vendargues :
- Massy :
- Olmet-et-Villecun :

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+guy yak I would understand this from Lasserre's POV as he lived there until his death last thursday, but what about the other villages where he has lived for years in a far and distant past? 
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lieven lebruyn

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Fresh(wo)men's course on Foundations

In two months I’ll be teaching ‘Logic and Set Theory’ for the first time, a first year, first semester course on Foundations. And no (though I considered it for a nanosecond) I will not trow HoTT at them…

There are few thing I like more than composing a new course. In the Belgian (university) system, a teacher is completely free to decide the content of his/her course. Clearly, there are the expectations of colleagues on what the course should (minimally) contain.

For this first semester, first year course I know I have to tell them about sets, maps, relations, truth tables, quantifiers, real numbers, and, perhaps, something about the axiom of choice and Zorn’s lemma. Btw.the guy in the picture  is Anders Zorn.

Earlier this week I began LaTeXing the notes, starting with the naive view on sets and their operations (intersection, union, subsets, power sets, products,…) and maps (images, inverse images, injective, surjective, bijective,…) but got quickly bored, as would be the students I guess.

The plan now will be to end this first 2 hour block with something a bit more fun: the notion of cardinality, proving that Q can be enumerated, Cantor’s diagonal argument that R cannot and, as a possible application of power sets, that here will always be a still higher cardinality.

I chuckled while typing the final line of that first session: “Nobody knows whether c=aleph1, that’s called the continuum hypothesis”… Hope this will blow their minds out, the first week of math-school.

The present plan of the other lessons can found on my new blog

All suggestions are welcome!

(Added august 3): Oops added a photograph of the wrong Zorn, Anders the artist, not Max the mathematician....
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+Toby Bartels "and furthermore we can PROVE that nobody knows! " : nice suggestion!
Anyway, im now TeXing completeness and compactness of propositional calculus, perhaps someone should clarify/clean up the mess Wikipidia makes of this.
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lieven lebruyn

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the 'Cemetery for Random Functions

N. Bourbaki was declared death (somewhat prematurely) in november 1968 by Jacques Roubaud (mathematician&Oulipo-poet). 

The announcement contains  a lot of mathematical jargon as well as a couple of riddles. I'm running a series of posts on them at my new blog.

Today I tried to decrypt this one:

The burial will take place in the cemetery for Random Functions (metro stations Markov and Godel) on Saturday November 23rd, 1968 at 3 o’clock in the afternoon.

the (or rather 'a') solution is here:

in a previous post there's an english translation of the announcement with links to all the obvious mathematics.

if you're in for a math-history puzzle, all corrections, suggestions or other solutions are appreciated!

Thanks to +Peter Luschny for posting the original of the death announcement here on G+ :
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Have him in circles
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Mathematician at UA
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mathematician by day, blogger by night
early adopter of noncommutative geometry, sceptic evangelist of the 'field with one element', passionate about a 400 year old chestnut farm somewhere in the Cevennes.
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