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    • added to the people-entry Edward Witten a paragraph Fields medal work with a commented list of articles that according to Atiyah won Witten the Fields medal in 1990.

    • brief category:people-entry for hyperlinking references

      v1, current

    • brief category:people-entry for hyperlinking references

      v1, current

    • Page created, but author did not leave any comments.

      v1, current

    • added pointer to

      • Mikhail Katz, David Sherry, Leibniz’s Infinitesimals: Their Fictionality, Their Modern Implementations, And Their Foes From Berkeley To Russell And Beyond (arXiv:1205.0174)

      where on the bottom of p. 9 I find

      Leibniz rejects nilsquare and nilcube infinitesimals, which are alto-gether incompatible with his approach to differential calculus,

      So if not Leibniz, who can be credited with first considering nilpotent infinitesimals?

      diff, v6, current

    • Brief idea of the E-string, pointer to and snippet from one reference that makes it nicely explicit.

      I am compiling this and related entries because we have a clean mathematical formalization of this zoo of structures now in terms of equivariant super homotopy theory (as surveyed here). Once everything is cleaned up and published, I will try to go through all the entries and accompany the vague Idea-sections with some solid mathematics.

      v1, current

    • Created page, more content to be added.

      v1, current

    • I have reorganized somewhat entry Maxim Kontsevich (with some new links and few bits of additional info) and created a related stub Vassiliev invariant, just to record a link to an impressive online bibliography maintained by Dror Bar-Natan and Sergei Duzhin, hosted at Duzhin's webpage at Russian Academy of Sciences.

    • Idea-section and one further reference at Thomason model structure.

      I remember Mike once said on the blog somewhere that there might be some problem with Thomason's original claim that cofibrant objects in this structure are posets. I made a brief remark on this, but I can't find Mike's original comment.

    • Kazama Suzuki models are a hallmark of constructing Superstring compactification with C=9, as required by internal consistency. Uses of it is varied, though a non-existing page of this topic on n Lab has surprised me.


      v1, current

    • I added the remark that the canonical model structure on Cat is the model structure obtained by transferring the projective model structure on bisimplicial sets.

    • I have touched H-space, slightly expanded here and there and slightly reorganized it.

    • Page created, but author did not leave any comments.

      v1, current

    • I noticed that the entry classifying space is in bad shape. I have added a table of contents and tried to structure it slightly, but much more needs to be done here.

      I have added a paragraph on standard classifying spaces for topological principal bundles via the geometric realization of the simplicial space associated to the given topological group.

      In the section “For crossed complexes” there is material that had been provided by Ronnie Brown which needs to be harmonized with the existing Idea-section. It proposes something like a general axiomatics on the notion of “classifying space” more than giving details on the geometric realization of crossed complexes

    • considerably expanded the entry strict 2-group.

      • Apart from adding an introductory discussion, and expanding the list of examples, in particular by adding that of automorphism 2-groups ...

      • ... I in particular give the detailed translation prescription for how to encode a 2-group by a crossed module at In terms of crossed modules

      This is to eventually serve as a supplement to the discussion at nonabelian group cohomology. So I spent some energy on disentangling the four different (though isomorphic) ways a crossed module gives rise to a 2-group (following my article with David Roberts).

    • I do think the phrasing “dense G δG_\delta set (i.e. a countable intersection of dense opens)” was a bit confusing, since “i.e.” means “in other words”, but here it applies only to the immediately preceding words “G δG_\delta set” rather than the entire phrase “dense G δG_\delta set”. So I changed it to “dense G δG_\delta set (i.e. a countable intersection of dense opens that is itself dense)”.

      diff, v13, current