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groen moet!

One week to go before the regional and European elections and tension is rising. For me there are two crucial questions : will a racist party get more than 20% of the votes? and will the green party get over the electoral threshold of 5%? If you are not Flemish both probably require some explanation.

A month ago, the extreme right party ‘Vlaams Blok’ was convicted in court for racism and discrimination. They can still participate in the elections because they appealed and Belgian courts are extremely slow. Many people think that this conviction only applies to the party and not to people voting for it. To me, anyone still voting for a party convicted for racism says “I don’t care about society, values and the law!”

Sadly, I wouldn’t be surprised if more than 20% of the electorate will broadcast that message next week. But let us remain optimistic and look at the Vlaams Blog weblogs and their posters ridiculing the Vlaams Blok propaganda.

Then there is the Flemish green party groen!.

Usually they got between 5% and 8% of the votes with one exception in 1999 when they obtained 11%. In 1999 they went into government and among major environmental accomplishments they also voted silly laws such as introducing an electoral threshold of 5%. In last year’s elections they were the first party to be hurt by this when they dived under 4% and had not a single member of parliament left.

I have voted green at every election with one exception : early 80ties the Americans wanted to install cruise missiles in Belgium and with my twenties-naivety I thought to be able to avoid this by casting a strategic (socialist) vote. A traumatic experience because soon afterwards the missiles were flown in…

To me this partly explains the reluctance of groen! to form an alliance with the socialist party as (sadly enough) groen! is run by people of my generation (or older).

Still, in the long run there is no alternative but to form one progressive green-red party. So, I hope that, whatever happens, after the elections competent youngsters such as Tinne Van der Straeten and Els Keytsman will take control of the green party and find equally driven people in the socialist party (not entirely trivial as they seem to specialize in babes whose major accomplishment is the introduction of the sleeveless shirt ministerial look).

In case you wonder : I will vote Tinne Van der Straeten for Europe and Lieve Stallaert for the Flemish

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capita selecta

Rather than going to the NOG
III Workshop
I think it is more fun to give a talk for the Capita
-course for 2nd year students on “Monstrous Moonshine”. If
I manage to explain to them at least something, I think I am in good
shape for next year\’s Baby Geometry (first year) course. Besides,
afterwards I may decide to give some details of Borcherds\’ solution next year in my 3rd year
Geometry-course…(but this may just be a little bit
Anyway, this is what I plan to do in my
lecture : explain both sides of the McKay-observation

196 884 = 196 883 + 1

that is, I\’ll give
the action of the modular group on the upper-half plane and prove that
its fundamental domain is just C using the modular j-function (left hand
side) and sketch the importance of the Monster group and its
representation theory (right hand side). Then I\’ll mention Ogg\’s
observation that the only subgroups Gamma(0,p)+ of SL(2,Z)
for which the fundamental domain has genus zero are the prime divisors
p of teh order of the Monster and I\’ll come to moonshine
conjecture of Conway and Norton (for those students who did hear my talk
on Antwerp sprouts, yes both Conway and Simon Norton (via his
SNORT-go) did appear there too…) and if time allows it, I\’ll sketch
the main idea of the proof. Fortunately, Richard Borcherds has written
some excellent expository papers I can use (see his papers-page and I also discovered a beautiful
moonshine-page by Helena Verrill which will make my job a lot
Btw. yesterday\’s Monster was taken from her other monster story…

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25 years monstrous moonshine

Writing a survey paper is a highly underestimated task. I once
tried it out with \’Centers of generic division algebras : the
rationality problem 1965-1990\’ and it took me a lot of time and that
was on a topic with only 10 to 15 key papers to consider… The task of
writing a survey paper on a topic with any breadth must be much more
difficult. Last week, Terry Gannon posted a survey paper on the arXiv :
Monstrous Moonshine : The first twenty-five years
which gives a very readable introduction to this exciting topic. It has
a marvelous opening line :

It has been approximately
twenty-five years since John McKay remarked that

196 884 = 196 883 +

Anyone who is puzzled by this line (“So what?”)
should definitely have a go at this paper! Still not convinced? Here is
the second sentence :

That time has seen the discovery of
important structures, the establishment of another deep connection
between number theory and algebra, and a reinforcement of a new era of
cooperation between pure mathematics and mathematical

For the remaining sentences (quite a few, the paper
is 33 pages long) I happily refer you to the paper.

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artistic and other frustrations

Yesterday, PD1 exhibited some of her paintings in the Antwerp Museum for Photography. Over breakfast this morning she was in a rare angry mood.

No, she was satisfied with the responses she got on her work, the room was not ideal (lighting etc.) but that was not what mattered…

Me : So?

She : There was this other work, a video-performance. I once saw by accident on Arte a short-film and this performance stole the whole idea of that film, from start to finish! The whole idea was nicked!

Me : Wake up! That’s the majority way of creating art, or science for that matter.

She : But it is so unfair! Why do people steal ideas ?

Me : Maybe they don’t see it as stealing. Maybe they believe they do a better thing with the original idea than the person who invented it.

She : Nothing can beat the original! Anyway, I find the most rewarding thing about art to come up with an original idea and work it out. It cannot be rewarding to steal other people\’s ideas.

Me (dry) : I think such people are after other rewards…

She : The same thing happens at school. Sometimes I come up with a suggestion to use a different technique or material and then a few weeks later, half of my class seems
to have worked this out too.

Me : So ? You still had the idea.

She : Yes, but the Jury doesn’t know that!

Me : So ? After the Jury you can still be confident to come up with new ideas, these others may fear they will only be able to repeat themselves.

She : But is it so unfair!

Me : What’s the alternative ? Are you going to lock yourself up in your room to
paint and let nobody see the result?

She : No, but I prefer to do my painting here at home, on my own with nobody looking over my shoulder constantly to see whether they can use some of my ideas. I will
paint on my own and only when it is fully finished they may see the result!

Me : That’s the spirit girl! You are much cleverer than I will ever be…

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a spider for Paul Smith’s list

of the best collections of links to homepages of people working in
non-commutative algebra and/or geometry is maintained by Paul Smith. At regular intervals I use it to check
up on some people, usually in vain as nobody seems to update their
homepage… So, today I wrote a simple spider to check for updates in
this list. The idea is simple : it tries to get the link (and when this
fails it reports that the link seems to be broken), it saves a text-copy
of the page (using lynx) on disc which it will check on a future
check-up for changes with diff. Btw. for OS X-people I got
lynx from the Fink Project. It then collects all data (broken
links, time of last visit and time of last change and recent updates) in
RSS-feeds for which an HTML-version is maintained at the geoMetry-site, again
using server side includes. If you see a 1970-date this means that I
have never detected a change since I let this spider loose (today).
Also, the list of pages is not alphabetic, even to me it is a surprise
how the next list will look. As I check for changes with diff the
claimed number of changed lines is by far accurate (the total of lines
from the first change made to the end of the file might be a better
approximation of reality… I will change this soon).
all of this is still experimental so please give me feedback if you
notice something wrong with these lists. Also I plan to extend this list
substantially over the next weeks (for example, Paul Smith himself is
not present in his own list…). So, if you want your pages to be
included, let me know at
For those on Paul\’s list, if you looked at your log-files today
you may have noticed a lot of traffic from as
I was testing the script. I\’ll keep my further visits down to once a
day, at most…

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arxiv RSS feeds available

you are interested in getting daily RSS-feeds of one (or more) of the
following arXiv
sections : math.RA, math.AG, math.QA and
math.RT you can point your news-aggregator to Most of the solution to my first
Perl-exercise I did explain already yesterday but the current program
has a few changes. First, my idea was to scrape the recent-files
from the arXiv, for example for math.RA I would get but this
contains only titles, authors and links but no abstracts of the papers.
So I thought I had to scrape for the URLs of these papers and then
download each of the abstracts-files. Fortunately, I found a way around
this. There is a lesser known way to get at all abstracts from
math of the current day (or the few last days) by using the Catchup interface. The syntax of this interface is
as follows : for example to get all math-papers with
posted on April 2, 2004 you have to get the page with

so in order to use it I had
to find a way to parse the present day into a numeric
day,month,year format. This is quite easy as there is the very
well documented Date::Manip-module in Perl. Another problem with
arXiv is that there are no posts in the weekend. I worked around
this by requesting the Catchup starting from the previous
business day
(an option of the DateCalc-function. This means
that over the weekend I get the RSS feeds of papers posted on Friday, on
Monday I\’ll get those of Friday&Monday and for all other days I\’ll get
those of today&yesterday. But it is easy to change the script to allow
for a longer period so please tell me if you want to have RSS-feeds for
the last 3 or 4 days. Also, if you need feeds for other sections that
can easily be done, so tell me.
Here are the URLs to give to
your news-aggregator for these sections :

math.RA at
math.QA at
math.RT at
math.AG at

your news-aggregator is not clever then you may have to add an
additional index.xml at the end. If you like to use these feeds
on a Mac, a good free news-aggregator is NetNewsWire Lite. To get at the above feeds, click on the Subscribe
and copy one of the above links in the pop-up window. I
don\’t think my Perl-script breaks the Robots Beware rule of the arXiv. All it does it to download one page a day
using their Catchup-Method. I still have to set up a cron-job to
do this daily, but I have to find out at which (local)time at night the
arXiv refreshes its pages…

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my first scraper

far as I know (but I am fairly ignorant) the arXiv does not
provide RSS feeds for a particular section, say mathRA. Still it would be a good idea for anyone
having a news aggregator to follows some weblogs and
news-channels having RSS syndication. So I decided to write one as my
first Perl-exercise and to my own surprise I have after a few hours work
a prototype-scraper for math.RA. It is not yet perfect, I still
have to convert the local URLs to global URLs so that they can be
clicked and at the moment I have only collected the titles, authors and
abstract-links whereas it would make more sense to include the full
abstract in the RSS feed, but give me a few more days…
basic idea is fairly simple (and based on an O\’Reilly hack).
One uses the Template::Extract module to
extract the goodies from the arXiv\’s template HTML. Maybe I am still
not used to Perl-documentation but it was hard for me to work out how to
do this in detail either from the hack or the online
module-documentation. Fortunately there is a good Perl Advent
page giving me the details that I needed. Once one has this
info one can turn it into a proper RSS-page using the XML::RSS-module.
In fact, I spend far
more time trying to get XML::RSS installed under OS X than
writing the code. The usual method, that is via

lieven$ sudo /usr/bin/perl -MCPAN -e shell Terminal does not support
AddHistory. cpan shell -- CPAN exploration and modules installation
(v1.76) ReadLine support available (try \'install
Bundle::CPAN\') cpan> install XML::RSS 

failed and even a
manual install for which the drill is : download the package from CPAN, go to the
extracted directory and give the commands

sudo /usr/bin/perl sudo make sudo make test sudo make

failed. Also a Google didn\’t give immediate results until
I did find this ADC page which set me on the right track.
It seems that the problem is in installing the XML::Parser for which one first need expat
to be installed. Now, the generic sourceforge page contains a
version for Linux but fortunately it is also part of the Fink
so I did a

sudo fink install expat

which worked
without problems but afterwards I still was not able to install
XML::Parser because Fink installs everything in the /sw
tree. But after

sudo perl EXPATLIBPATH=/sw/lib

I finally got the manual installation
going. I will try to tidy up the script over the weekend…

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just finished the formal lecture-part of the course Projects in
non-commutative geometry
(btw. I am completely exhausted after this
afternoon\’s session but hopeful that some students actually may do
something with my crazy ideas), springtime seems to have arrived and
next week the easter-vacation starts so it may be time to have some fun
like making a new webpage (yes, again…). At the moment the main page is not really up to standards
and Raf and Hans will be using it soon for the information about the
Liegrits-project (at the moment they just have a beautiful logo). My aim is to make the main page to be the
starting page of the geoMetry site
(guess what M stands for ?) on which I want
to collect as much information as possible on non-commutative geometry.
To get at that info I plan to set some spiders or bots or
scrapers loose on the web (this is just an excuse to force myself
to learn Perl). But it seems one has to follow strict ethical guidelines
in doing so. One of the first sites I want to spider is clearly the arXiv but they have
a scary Robots Beware page! I don\’t know whether their
robots.txt file will allow me to get at any of
their goodies. In a robots.txt file the webmaster can put the
directories on his/her site which are off limits to robots and as I
don\’t want to do anything that may cause that the arXiv is no longer
available to me (or even worse, to the whole department) I better follow
these guidelines. First site on my list to study tomorrow will be The
Web Robots Pages

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Borcherds’ monster papers

Yesterday morning I thought that I could use some discussions I had a
week before with Markus Reineke to begin to make sense of one
sentence in Kontsevich’ Arbeitstagung talk Non-commutative smooth
spaces :

It seems plausible that Borcherds’ infinite rank
algebras with Monstrous symmetry can be realized inside Hall-Ringel
algebras for some small smooth noncommutative

However, as I’m running on a 68K RAM-memory, I
didn’t recall the fine details of all connections between the monster,
moonshine, vertex algebras and the like. Fortunately, there is the vast
amount of knowledge buried in the arXiv and a quick search on Borcherds gave me a
list of 17 papers. Among
these there are some delightful short (3 to 8 pages) expository papers
that gave me a quick recap on things I once must have read but forgot.
Moreover, Richard Borcherds has the gift of writing at the same time
readable and informative papers. If you want to get to the essence of
things in 15 minutes I can recommend What
is a vertex algebra?
(“The answer to the question in the title is
that a vertex algebra is really a sort of commutative ring.”), What
is moonshine?
(“At the time he discovered these relations, several
people thought it so unlikely that there could be a relation between the
monster and the elliptic modular function that they politely told McKay
that he was talking nonsense.”) and What
is the monster?
(“3. It is the automorphism group of the monster
vertex algebra. (This is probably the best answer.)”). Borcherds
maintains also his homepage on which I found a few more (longer)
expository papers : Problems in moonshine and Automorphic forms and Lie algebras. After these
preliminaries it was time for the real goodies such as The
fake monster formal group
, Quantum vertex algebras and the like.
After a day of enjoyable reading I think I’m again ‘a point’
wrt. vertex algebras. Unfortunately, I completely forgot what all this
could have to do with Kontsevich’ remark…

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chicken of the VNC

If I
ever get our home automation system configured I’ll use my (partly
broken) old iBook as my Indigo-server (or my MisterHouse-server when I brush up my
Perl-knowledge). It should then run quietly put away somewhere and I
don’t want to take it out every time I want to add another routine to
the program.
Fortunately there is a way to do this by turning
the iBook into a VNC-server, where VNC stands for
Virtual Network Computer. Here is how RealVNC describes

VNC (Virtual Network Computing) software makes it
possible to view and fully-interact with one computer from any other
computer or mobile device anywhere on the Internet. VNC software is
cross-platform, allowing remote control between different types of
computer. For ultimate simplicity, there is even a Java viewer, so that
any desktop can be controlled remotely from within a browser without
having to install software.

But can all this be done under
Mac OS X without too much hassle? The first step is to download
OSXvnc and install it on the iBook. Some of the
sourceforge-sites do not seem to have this package, but fortunately some
still do. Installation is no problem and when you fire OSXvnc up
you have to fill in a password which you need later to connect to your
OSXvnc-server (the iBook). Most other options one can leave at their
default values but in the Startup-pane it is useful to click on
the Configure Startup Item button. When all this is done, press
the Start button to launch the VNC-server.
Next step is
to go to the computer you want to use to control the VNC-server (an iMac
in my case). On it one needs to install the Chicken of the VNC software which makes the iMac
into a VNC-client. Fire it up and fill out the Host (the name of
your OSXvnc-server, iBookLieven.local in my case) and the
Password (the one of the OSXvnc-server program), press the
Connect button and the screen of your VNC-server will appear
which you can control with your mouse as if you were actually working on
the thing. Very handy as I managed to break the touch-control on my
iBook when installing a new hard-drive and I need the only USB-port to
connect to the X10-network…

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