Martins-Porter paper

Martins-Porter paper

[John Baez]

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Interesting letter from Grothendieck!

Ronnie Brown writes:

>A recent arXiv paper by Jo=E3o Faria Martins and Tim Porter
>math.QA/0608484
>Title: On Yetter's Invariant and an Extension of the Dijkgraaf-Witten
>Invariant to Categorical Groups
>
> seems also relevant to the theme of the Baez-Shulman notes.

Yes; we didn't get into TQFTs at all in our notes, but Martins
and Porter use the classifying space of a discrete 2-group
(=3D categorical group =3D crossed module =3D gr-category) in their
construction, and that's quite relevant.

I wrote a little introduction to the Martins-Porter paper and its
antecedents at the n-category cafe:

http://golem.ph.utexas.edu/category/2006/08/categorifying_the_dijkgraafwit.=
html

Best,
jb

Martins-Porter paper

[John Baez]

jim stasheff wrote:

> link didn't work
> even if I tacked the html onto the =

Sorry, the equals sign should not be there.  Here's the link
to the Martins-Porter paper on categorifying the Dijkgraaf-Witten
model:

http://golem.ph.utexas.edu/category/2006/08/categorifying_the_dijkgraafwit.html

and here, just for fun, is a letter from Grothendieck to Ronnie Brown:

http://golem.ph.utexas.edu/category/2006/08/letter_from_grothendieck.html

Best,
jb