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the n-category cafe

I’ve
often argued here that the only way to keep a mathematical blog going
over time is to change it into a group-blog. At times, I’ve even
approached some people directly asking them to contribute but with no
success, so far. (Btw. I’ve given up on this, but in case you changed
your mind, you know where to find me). Still, it
is nice to see that some people succeed where I’ve failed. For a few
weeks now, a brand-new group blog is producing posts at an amazing rate
: The n-category
cafe
. The contributors are John Baez (also known from his
This Week’s Finds in
Mathematical Physics
), David Corfield (also
known from his blog Philosophy of
Real Mathematics
) and Urs Schreiber (also
known as a contributor to The String Coffee Table ).
The blog’s subtitle ‘A group blog on math, physics and philosophy’
promises a wider range of topics than the mainly categorical stuff
posted so far (perhaps, they will open up their cafe at a later date to
others willing to contribute?)

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simple group of order 2

The Klein Four Group is an a
capella group from the maths department of Northwestern. Below a link to
one of their songs (grabbed from P.P. Cook’s Tangent Space
).

Finite
Simple Group (of order two)

A Klein Four original by
Matt Salomone


The path of love is never
smooth
But mine’s continuous for you
You’re the upper bound in the chains of my heart
You’re my Axiom of Choice, you know it’s true
But lately our relation’s not so well-defined
And
I just can’t function without you
I’ll prove my
proposition and I’m sure you’ll find
We’re a
finite simple group of order two
I’m losing my
identity
I’m getting tensor every day
And
without loss of generality
I will assume that you feel the same
way
Since every time I see you, you just quotient out
The faithful image that I map into
But when we’re
one-to-one you’ll see what I’m about
‘Cause
we’re a finite simple group of order two
Our equivalence
was stable,
A principal love bundle sitting deep inside
But then you drove a wedge between our two-forms
Now
everything is so complexified
When we first met, we simply
connected
My heart was open but too dense
Our system
was already directed
To have a finite limit, in some sense

I’m living in the kernel of a rank-one map
From my
domain, its image looks so blue,
‘Cause all I see are
zeroes, it’s a cruel trap
But we’re a finite simple
group of order two
I’m not the smoothest operator in my
class,
But we’re a mirror pair, me and you,
So
let’s apply forgetful functors to the past
And be a
finite simple group, a finite simple group,
Let’s be a
finite simple group of order two
(Oughter: “Why not
three?”)
I’ve proved my proposition now, as you
can see,
So let’s both be associative and free
And by corollary, this shows you and I to be
Purely
inseparable. Q. E. D.

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noncommutative Fourier transform

At the
noncommutative algebra program in MSRI 1999/2000, Mikhail Kapranov gave
an intriguing talk Noncommutative neighborhoods and noncommutative Fourier transform
and over the years I’ve watched the video of this talk a number
of times. The first part of the talk is about his work on Noncommutative geometry
based on commutator expansions
and as I’ve once worked through it
this part didn’t present problems. On the other hand, I’ve never
understood much from the second part of the talk which claims to relate
these noncommutative formal neighborhoods to _noncommutative Fourier
transforms_. The string coffee table has a post Kapranov
and Getzler on Higher Stuff
linking to two recent talks by Kapranov
on noncommutative Fourier transforms at the Streetfest. Marni
Sheppeard made handwritten notes available. I definitely should find the time
to get through them and have another go at the Kapranov-video…

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