# Category: rants

I’m back in Antwerp for over a week now, and finally got hold of our copy of Shimura’s “Introduction to the arithmetic theory of automorphic functions”.

The sad story of disappearing libraries at our university, and possibly elsewhere (everywhere?).

Over 20 years ago our maths department shared a building with the language departments, as well as a library.

The ground floor was taken up by languages, science books were in the cellar. There were years I spend more time on the ground floor than in the maths section.

I must have read most of the Dutch novels published between 1980 and 2000. For some time I could even pass as a Joyce-scholar, at least to those interested in a tiny part of Finnegans Wake.

All that changed when they united the three different branches of Antwerp university and we had to move to another campus.

We were separated from the language departments (they moved to the center of town) and, sadly, also from their library.

On the positive side, we moved to a nice building with a gorgeous library. And, an added bonus, it was on the same floor as my office. To kill an hour it was fun to stroll over to the library and spend some time between books and journals.

Then, some years ago, they closed down the maths-library and moved a tiny fraction of it to the science-library (located at a different campus).

Administration argued that too few people visited the library to keep it open.

But more important, they needed the space to create what they call a ‘study landscape’: a lounge where students can hang out, having enough power outlets for all their computers and smartphones.

So, the maths-library had to go for a place where, during term, students can recharge their phones, and during examination periods like now, students can sit together to study.

It seems that millennials need to have visual confirmation that their fellow students are also offline.

Today even the science-library is transformed into such a study-landscape, and only a handful of math-books remain on the shelves (well-hidden behind another door).

For the few odd ones, like me, who still want to browse through a book occasionally, you have to request for it online.

A few days later you get an email saying that your request is granted (they make it sound as if this is a huge favour), and then they need some more days to get the book from the storehouse and deliver it (sometimes randomly) to one of the few remaining university libraries, sorry, study landscapes…

Smullyan found himself in a very strange country indeed!

All the inhabitants of this country are completely truthful – they always tell you honestly what they believe, but the trouble is that about half of the population are totally mad, and all their beliefs are wrong!

The other half are totally sane and accurate in their judgments, all their beliefs are correct.

Smullyan felt honoured to be invited by the Presidential couple.

The President was the only one who said anything, and what he said was:

“My wife once said that I believe that she believes I am mad.”

What can be deduced about the President’s sanity, and that of his wife?

Reference: This is a minor adaptation of Problem 4.5 in Raymond Smullyan‘s book Logical Labyrinths.

My one and only resolution for 2018: ban vampires from my life!

Here’s the story.

In the 1920’s, Montparnasse was at the heart of the intellectual and artistic life in Paris because studios and cafés were inexpensive.

Artists including Picasso, Matisse, Zadkine, Modigliani, Dali, Chagall, Miro, and the Romanian sculptor Constantin Brancusi all lived there.

You’ll find many photographs of Picasso in the company of others (here center, with Modigliani and Salmon), but … not with Brancusi.

From A Life of Picasso: The Triumphant Years, 1917-1932 (Vol 3) by John Richardson:

“Brancusi disapproved of one of of Picasso’s fundamental characteristics—one that was all too familiar to the latter’s fellow artists and friends—his habit of making off not so much with their ideas as with their energy. “Picasso is a cannibal,” Brancusi said. He had a point. After a pleasurable day in Picasso’s company, those present were apt to end up suffering from collective nervous exhaustion. Picasso had made off with their energy and would go off to his studio and spend all night living off it. Brancusi hailed from vampire country and knew about such things, and he was not going to have his energy or the fruits of his energy appropriated by Picasso.”

I learned this story via Austin Kleon who made this video about it:

Earlier today, John Duncan (of moonshine fame) emailed he was unable to post a comment to the previous post:

There’s little point in maintaining a self-hosted blog if people cannot comment on it. If you tried, you got this scary message:

Catchable fatal error: Object of class WP_Error could not be converted to string in /wp-includes/formatting.php on line 1031

The days I meddled with wordpress core php-files are long gone, and a quick Google search didn’t come up with anything helpful.

In despair, there’s always the database to consider.

Here’s a screenshot of this blog’s database in phpMyAdmin:

No surprise you cannot comment here, there isn’t even a wp_comments table in the database! (though surprisingly, there’s a table wp_commentmeta…)

Two weeks ago I moved this blog to a new iMac. Perhaps the database got corrupted in the process, or the quick export option of phpMyAdmin doesn’t include comments (unlikely), or whatever.

Here’s what I did to get things working again. It may solve your problem if you don’t have a backup of another wordpress-blog with a functional wp_comments table.

1. Set up a new WordPress blog in the usual way, including a new database, let’s call it ‘newblog’.

3. Export your blog’s database, say ‘oldblog’, via the ‘quick export’ option in phpMyAdmin to get a file oldblog.sql.

4. If this file is small you can use phpMyAdmin to import it into newblog. If not you need to do it with this terminal-command

mysql -h localhost -u root – p newblog < oldblog.sql

and have the patience for this to finish.

5. Change in your wp-config file the oldblog database to newblog.

Happy commenting!

Please allow for a couple of end-of-semester bluesy ramblings. I just finished grading the final test of the last of five courses I lectured this semester.

Most of them went, I believe, rather well.

As always, it was fun to teach an introductory group theory course to second year physics students.

Personally, I did enjoy our Lie theory course the most, given for a mixed public of both mathematics and physics students. We did the spin-group $SU(2)$ and its connection with $SO_3(\mathbb{R})$ in gruesome detail, introduced the other classical groups, and proved complete reducibility of representations. The funnier part was applying this to the $U(1) \times SU(2) \times SU(3)$-representation of the standard model and its extension to the $SU(5)$ GUT.

Ok, but with a sad undertone, was the second year course on representations of finite groups. Sad, because it was the last time I’m allowed to teach it. My younger colleagues decided there’s no place for RT on the new curriculum.

Soit.

The final lecture is often an eye-opener, or at least, I hope it is/was.

Here’s the idea: someone whispers in your ear that there might be a simple group of order $60$. Armed with only the Sylow-theorems and what we did in this course we will determine all its conjugacy classes, its full character table, and finish proving that this mysterious group is none other than $A_5$.

Right now I’m just a tad disappointed only a handful of students came close to solving the same problem for order $168$ this afternoon.

Clearly, I gave them ample extra information: the group only has elements of order $1,2,3,4$ and $7$ and the centralizer of one order $2$ element is the dihedral group of order $8$. They had to determine the number of distinct irreducible representations, that is, the number of conjugacy classes. Try it yourself (Solution at the end of this post).

For months I felt completely deflated on Tuesday nights, for I had to teach the remaining two courses on that day.

There’s this first year Linear Algebra course. After teaching for over 30 years it was a first timer for me, and probably for the better. I guess 15 years ago I would have been arrogant enough to insist that the only way to teach linear algebra properly was to do representations of quivers…

Now, I realise that linear algebra is perhaps the only algebra course the majority of math-students will need in their further career, so it is best to tune its contents to the desires of the other colleagues: inproducts, determinants as volumes, Markov-processes and the like.

There are thousands of linear algebra textbooks, the one feature they all seem to lack is conciseness. What kept me going throughout this course was trying to come up with the shortest proofs ever for standard results. No doubt, next year the course will grow on me.

Then, there was a master course on algebraic geometry (which was supposed to be on scheme theory, moduli problems such as the classification of fat points (as in the car crash post, etale topology and the like) which had a bumpy start because class was less prepared on varieties and morphisms than I had hoped for.

Still, judging on the quality of the papers students are beginning to hand in (today I received one doing serious stuff with stacks) we managed to cover a lot of material in the end.

I’m determined to teach that first course on algebraic geometry myself next year.

Which brought me wondering about the ideal content of such a course.

Half a decade ago I wrote a couple of posts such as Mumford’s treasure map, Grothendieck’s functor of points, Manin’s geometric axis and the like, which are still quite readable.

In the functor of points-post I referred to a comment thread Algebraic geometry without prime ideals at the Secret Blogging Seminar.

As I had to oversee a test this afternoon, I printed out all comments (a full 29 pages!) and had a good time reading them. At the time I favoured the POV advocated by David Ben-Zvi and Jim Borger (functor of points instead of locally ringed schemes).

Clearly they are right, but then so was I when I thought the ‘right’ way to teach linear algebra was via quiver-representations…

We’ll see what I’ll try out next year.

You may have wondered about the title of this post. It’s derived from a paper Raf Bocklandt (of the Korteweg-de Vries Institute in Amsterdam) arXived some days ago: Reflections in a cup of coffee, which is an extended version of a Brouwer-lecture he gave. Raf has this to say about the Brouwer fixed-point theorem.

“The theorem is usually explained in worldly terms by looking at a cup of coffee. In this setting it states that no matter how you stir your cup, there will always be a point in the liquid that did not change position and if you try to move that part by further stirring you will inevitably move some other part back into its original position. Legend even has it that Brouwer came up with the idea while stirring in a real cup, but whether this is true we’ll never know. What is true however is that Brouwers refections on the topic had a profound impact on mathematics and would lead to lots of new developments in geometry.”

I wish you all a pleasant end of 2016 and a much better 2017.

As to the 168-solution: Sylow says there are 8 7-Sylows giving 48 elements of order 7. The centralizer of each of them must be $C_7$ (given the restriction on the order of elements) so two conjugacy classes of them. Similarly each conjugacy class of an order 3 element must contain 56 elements. There is one conjugacy class of an order 2 element having 21 elements (because the centralizer is $D_4$) giving also a conjugacy class of an order 4 element consisting of 42 elements. Together with the identity these add up to 168 so there are 6 irreducible representations.