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    • Look at what has been happening at derivator. The entry was erased and various things put there by an Anonymous Coward. Another one has reinstated the original one!! Has anyone noticed this? I was travelling about the time it happened so my usual check did not occur.

      At triangle identities something similar had started. I have rolled back.

    • Was this meant to be Planck Collaboration? I have renamed it!

    • I moved much of material from Hopf algebroid to Hopf algebroid over a commutative base, where both groupoid convolution algebras and group function algebras belong there. Most of the difference is seen already at the level of bialgebroid, the stuff about antipode in general case is to be written. Some more changes to both entries.

    • For some reason, we never had map redirect to function, but now we do. Same with mapping.

      This may or may not be the best behaviour. We might actually want a page on how people distinguish these words, such as in topology (‘map’ = continuous map but ‘function’ = function, maybe).

    • started field (physics).

      So far there is an Idea-section, a general definition with some remarks, and the beginning of a list of examples, which after the first spelled out (gravity) becomes just a list of keywords for the moment.

      More later.

    • Created binary Golay code. The construction is a little involved, and I haven’t put it in yet, because I think I can nut out a nicer description. The construction I aim to describe, in slightly different notation and terminology is in

      R. T. Curtis (1976). A new combinatorial approach to M24. Mathematical Proceedings of the Cambridge Philosophical Society, 79, pp 25-42. doi:10.1017/S0305004100052075.

    • added to some relevant entries a pointer to

    • added to Hilbert bimodule a pointer to the Buss-Zhu-Meyer article on their tensor products and induced 2-category structure.

    • I have now created relative category.

      Question: Does the transferred model structure on RelCat\mathbf{RelCat} resolve Rezk’s [2001] conjecture that the classification diagram of a model category is weakly equivalent to its simplicial localisation? The N ξN_\xi functor looks very close to computing the hammock localisation to me…

    • I have added to groupoid convolution algebra the beginning of an Examples-section titled Higher groupoid convolution algebras and n-vector spaces/n-modules.

      Conservatively, you can regard this indeed as just some examples of applications of the groupoid convolution algebra construction. But the way it is presented is supposed to be suggestive of a “higher C*-algebra” version of convolution algebras of higher Lie groupoids.

      I have labelled it as “under construction” to reflect the fact that this latter aspect is a bit experimental for the moment.

      The basic idea is that to the extent that we do have groupoid convolution as a (2,1)-functor

      C:GrpdAlg b op2Mod C \colon Grpd \to Alg_{b}^{op} \simeq 2Mod

      (as do do for discrete geometry and conjecturally do for smooth geometry), then this immediately means that it sends double groupoids to convolution sesquialgebras, hence to 3-modules with basis (3-vector spaces).

      As the simplest but instructive example of this I have spelled out how the ordinary dual(commutative and non-co-commutative) Hopf algebra of a finite group arises this way as the “horizontally constant” double groupoid incarnation of BG\mathbf{B}G, while the convolution algebra of GG is the algebra of the “vertically discrete” double groupoid incarnation of BG\mathbf{B}G.

      But next, if we simply replace the bare Alg b op2ModAlg_b^{op} \simeq 2 Mod with the 2-category C *Alg bC^\ast Alg_b of C *C^\ast-algebras and Hilbert bimodules between them and assume (as seems to be the case) that C *C^\ast-algebraic groupoid convolution is a 2-functor

      LieGrpd C *Alg n op LieGrpd_{\simeq} \to C^\ast Alg_n^{op}

      then the same argument goes through as before and yields convolution “C *C^\ast-2-algebras” that look like Hopf-C*-algebras. Etc. Seems to go in the right direction…

    • seeing the announcement of that diffiety summer school made me think that we should have a dedicated entry titled cohomological integration which points to the aspects of this discussed already elswhere on the nLab, and which eventually lists dedicated references, if any. So I created a stub.

      Does anyone know if there is a published reference to go with the relevant diffiety-school page ?

    • dropped some lines into a new Properties-section in the old and neglected entry bibundle. But not for public consumption yet.

    • I felt we were lacking an entry closure operator. I have started one, but don’t have more time now. It’s left in a somewhat sad incomplete state for the moment.

    • I could have sworn that we already had entries like “topological ring”, “topological algebra” or the like. But maybe we don’t, or maybe I am looking for the wrong variant titles.

      I ended up creating a stub for topological algebra now…

    • I have added to C-star algebra the statement that the image of a C *C^\ast-algebra under an *\ast-homomorphism is again C *C^\ast.

      Also reorganized the Properties-section a bit and added more references.

    • the entry groupoid could do with some beautifying.

      I have added the following introductory reference:

      • Alan Weinstein, Groupoids: Unifying Internal and External Symmetry – A Tour through some Examples, Notices of the AMS volume 43, Number 7 (pdf)
    • I have started adding some references to

      on modules (C *C^\ast-modules) of (continuous, etc..) convolution algebras of topological/Lie groupoids.

      I still need to look into this more closely. A motivating question for this kind of thing is:

      what’s the right fine-tuning of the definition of modules over twisted Lie groupoid convolution algebras such that for centrally extended Lie groupoids it becomes equivalent to the corresponding gerbe modules?

      This seems fairly straightforward, but there are is some technical fine-tuning to deal with. I was hoping this is already stated cleanly in the literature somewhere. But maybe it is not. Or maybe I just haven’t seen it yet.

    • Wrote a quick note at centrally extended groupoid and interlinked a little, for the moment just motivated by having the link point somwhere.

    • as mentioned in another thread, I have expanded the Idea-section at polarization in order to highlight the relation to canonical momenta (which I also edited accordingly).

    • felt like making a terminological note on phase and phase space in physics (and linked to it from the relevant entries).

      If anyone has more information on the historical origin of the term “phase space”, please let me know.

    • started a dismabiguation page for phase. Feel invited to add further meanings.

    • Just in case you see me editing in the Recently Revised list and are wondering:

      I have created and have started to fill some content into semiclassical state. But I am not done yet and the entry is not in good shape yet. So don’t look at yet it unless in a mood for fiddling and editing.

    • I started an entry classical-to-quantum notions - table for inclusion in “Related concepts”-sections in the relevant entries.

      This is meant to clean up the existing such “Related concepts”-lists. But I am not done yet with the cleaning-up…

    • New entry semiclassical approximation. It requires a careful choice of references. The ones at the wikipedia article are catastrophically particular, 1-dimensional, old and non-geometric and hide the story more than reveal. Stub Maslov index containing the main references for Maslov index.