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- Discussion Type
- discussion topicconcept with an attitude
- Category Latest Changes
- Started by Urs
- Comments 21
- Last comment by Oscar_Cunningham
- Last Active Feb 7th 2020

This is maybe mainly for entertainment. But don’t forget that for newcomers there is a real issue here which may well be worth explaining:

In mathematics it happens at times that one and the same concept is given two different names to indicate a specific perspective, a certain attitude as to what to do whith such objects.

Here are examples:

A

*quiver*is just a directed graph (pseudograph, to be explicit). But one says*quiver*instead of*directed graph*when one is interested in studying*quiver representations*: functors from the free category on that graph to the category of finite-dimensional vector spaces.A

*presheaf*is just a contravariant functor. But one says*presheaf*instead of*contravariant functor*when one is interested in studying its sheafification, or even if one is just intersted in regarding the category of functors with its structure of a topos: the presheaf topos.

(…)

- Discussion Type
- discussion topicJens Eisert
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 7th 2020

brief

`category:people`

-entry for hyperlinking references at*tensor network*and at*holographic entanglement entropy*

- Discussion Type
- discussion topicholographic entanglement entropy
- Category Latest Changes
- Started by Urs
- Comments 10
- Last comment by Urs
- Last Active Feb 7th 2020

created a stub for

*holographic entanglement entropy*in reaction to this MO question.

- Discussion Type
- discussion topicRoman Orus
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 7th 2020

brief

`category:people`

-entry for hyperlinking references at*tensor network*

- Discussion Type
- discussion topicstring diagram
- Category Latest Changes
- Started by nLab edit announcer
- Comments 30
- Last comment by nLab edit announcer
- Last Active Feb 7th 2020

- Discussion Type
- discussion topicUli Wagner
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 7th 2020

brief

`category:people`

-entry for hyperlinking references at*computational topology*

- Discussion Type
- discussion topicBruhat-Tits tree
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 7th 2020

a stub for the moment just so as to give a home to

- Bill Casselman,
*The Bruhat-Tits tree of $\mathrm{SL}(2)$*, 2014 (pdf, CasselmanOnBruhatTitsTree2014.pdf:file)

and to cross-link with

*p-adic AdS/CFT correspondence*and*tensor network states*.- Bill Casselman,

- Discussion Type
- discussion topiclambda-ring
- Category Latest Changes
- Started by Stephan A Spahn
- Comments 7
- Last comment by nLab edit announcer
- Last Active Feb 7th 2020

I edited lambda-ring, added a definition from the thesis of John R. Hopkins. Later on I will add the definitions of Hazewinkel, too. This entry has a long (and very instructive) idea-section. Maybe I find time to fill in some more details to these ideas.

- Discussion Type
- discussion topiccosmic inflation
- Category Latest Changes
- Started by Urs
- Comments 15
- Last comment by Urs
- Last Active Feb 7th 2020

stub for

*cosmic inflation*(for the moment just to record some references)

- Discussion Type
- discussion topicJoseph Polchinski
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 7th 2020

added pointer to today’s

- Raphael Bousso, Fernando Quevedo, Steven Weinberg,
*Joseph Polchinski: A Biographical Memoir*(arXiv:2002.02371)

- Raphael Bousso, Fernando Quevedo, Steven Weinberg,

- Discussion Type
- discussion topicAdS2-CFT1 -- references
- Category Latest Changes
- Started by Urs
- Comments 3
- Last comment by Urs
- Last Active Feb 6th 2020

- Discussion Type
- discussion topicquasicrystal
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 6th 2020

- Discussion Type
- discussion topictranscendental ideal
- Category Latest Changes
- Started by Thomas Holder
- Comments 1
- Last comment by Thomas Holder
- Last Active Feb 6th 2020

- Discussion Type
- discussion topicwell group
- Category Latest Changes
- Started by Urs
- Comments 2
- Last comment by Urs
- Last Active Feb 6th 2020

- Discussion Type
- discussion topicbooks about string theory
- Category Latest Changes
- Started by Urs
- Comments 4
- Last comment by Urs
- Last Active Feb 6th 2020

at books about string theory I have added some paragraphs with descriptions of books in the first section (“Mathematically inclined monographs about string theory”)

- Discussion Type
- discussion topicstrange metal
- Category Latest Changes
- Started by Urs
- Comments 3
- Last comment by Urs
- Last Active Feb 6th 2020

- Discussion Type
- discussion topicknot invariant
- Category Latest Changes
- Started by Urs
- Comments 5
- Last comment by Urs
- Last Active Feb 6th 2020

I see that Ben Webster was so kind to start knot invariant.

That nicely supplies linkes for Bruce's recent Chern-Simons theory

- Discussion Type
- discussion topicHubert Wagner
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 6th 2020

brief

`category:people`

-entry for hyperlinking references at*cohomotopy*

- Discussion Type
- discussion topicAdS-CFT in condensed matter physics
- Category Latest Changes
- Started by Urs
- Comments 6
- Last comment by Urs
- Last Active Feb 6th 2020

- Discussion Type
- discussion topicfuzzy sphere
- Category Latest Changes
- Started by Urs
- Comments 12
- Last comment by Urs
- Last Active Feb 5th 2020

- Discussion Type
- discussion topicChristopher Herzog
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 5th 2020

- Discussion Type
- discussion topicsuperconductivity
- Category Latest Changes
- Started by Urs
- Comments 2
- Last comment by Urs
- Last Active Feb 5th 2020

added pointer to:

- Sean Hartnoll, Andrew Lucas, Subir Sachdev, Section 6.3 of:
*Holographic quantum matter*, MIT Press 2018 (arXiv:1612.07324, publisher)

- Sean Hartnoll, Andrew Lucas, Subir Sachdev, Section 6.3 of:

- Discussion Type
- discussion topicprobability theory
- Category Latest Changes
- Started by David_Corfield
- Comments 3
- Last comment by nLab edit announcer
- Last Active Feb 5th 2020

Strangely, we don’t seem to have an nForum discussion for probability theory.

I added a reference there to

- Chris Heunen, Ohad Kammar, Sam Staton, Hongseok Yang,
*A Convenient Category for Higher-Order Probability Theory*, (arXiv:1701.02547)

It replaces the category of measurable spaces, which isn’t cartesian closed, with the category of quasi-Borel spaces, which is. As they point out in section IX, what they’re doing is working with concrete sheaves on an established category of spaces, rather like the move to diffeological spaces.

[Given the interest in topology around these parts at the moment, we hear of ’C-spaces’ as generalized topological spaces arising from a similar sheaf construction in C. Xu and M. Escardo, “A constructive model of uniform continuity,” in Proc. TLCA, 2013.]

- Chris Heunen, Ohad Kammar, Sam Staton, Hongseok Yang,

- Discussion Type
- discussion topicmulti-trace operator
- Category Latest Changes
- Started by Urs
- Comments 5
- Last comment by Urs
- Last Active Feb 5th 2020

- Discussion Type
- discussion topicnaturalness
- Category Latest Changes
- Started by Urs
- Comments 2
- Last comment by Urs
- Last Active Feb 5th 2020

on the occasion of adding one more recent reference (Wells 18) I gave the paragraphs criticizing the concept their own subsection

*Problems with the concept*.And then I took the liberty to add what I think is the key problem, which is however generally overlooked in these discussions, away from the small community of mathematical field theorists:

*Dependence on the renormalization scheme*

- Discussion Type
- discussion topicmonoidal monad
- Category Latest Changes
- Started by Todd_Trimble
- Comments 6
- Last comment by Sam Staton
- Last Active Feb 4th 2020

Started an article on monoidal monad. An earlier redirect had sent it over to Hopf monad which is something that Zoran was working on, but I think it deserves an article to itself, with discussion of the relation to commutative monads, etc. (which I have started).

- Discussion Type
- discussion topicBousfield–Kan spectral sequence
- Category Latest Changes
- Started by DavidJaz
- Comments 1
- Last comment by DavidJaz
- Last Active Feb 3rd 2020

- Discussion Type
- discussion topictensor product of algebras over a commutative monad
- Category Latest Changes
- Started by PaoloPerrone
- Comments 5
- Last comment by PaoloPerrone
- Last Active Feb 3rd 2020

- Discussion Type
- discussion topicSachdev-Ye-Kitaev model
- Category Latest Changes
- Started by Urs
- Comments 16
- Last comment by Urs
- Last Active Feb 3rd 2020

- Discussion Type
- discussion topicAndrew Lucas
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active Feb 3rd 2020

brief

`category:people`

-entry for hyperlinking references at AdS/CFT in condensed matter physics