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    • I am moving the following old query box exchange from orbifold to here.

      old query box discussion:


      I am confused by this page. It starts out by boldly declaring that “An orbifold is a differentiable stack which may be presented by a proper étale Lie groupoid” but then it goes on to talk about the “traditional” definition. The traditional definition definitely does not view orbifolds as stacks. Neither does Moerdijk’s paper referenced below — there orbifolds form a 1-category.

      Personally I am not completely convinced that orbifolds are differentiable stacks. Would it not be better to start out by saying that there is no consensus on what orbifolds “really are” and lay out three points of view: traditional, Moerdijk’s “orbifolds as groupoids” (called “modern” by Adem and Ruan in their book) and orbifolds as stacks?

      Urs Schreiber: please, go ahead. It would be appreciated.


      end of old query box discussion

    • I tried to explain what a superselection sector is which is less easy than one would think…of course what I would really like to do is to explain some DHR-superselection theory and there one can of course cite the mathematical definition without any further explanation of the origins :-)

    • Started pure subobject. I wish someone would tell me the intuitive reason for their importance though!

    • Comment about Ackermann function. I don’t know what Ackermann originally wrote, but most texts use A_0(m)=m+1, if I understand correctly.

      diff, v18, current

    • Edit to: intersecting D-brane model by Urs Schreiber at 2018-04-01 00:55:01 UTC.

      Author comments:

      hyperlinked pointer to textbook by Ibanez-Uranga

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

      • William Lawvere, Functional Remarks on the General Concept of Chaos , IMA reprint 87, 1984 (pdf)

      v1, current

    • just for completeness, and to make links work

      v1, current

    • Fixed pdf link to “Towards an understanding of Girard’s transcendental syntax”

      ALH

      diff, v6, current

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

      v1, current

    • some minimum, in order to give a home to today’s

      • Dong-Yang Wang, Ya-Dong Yang, Xing-Bo Yuan, bcτν¯b \to c \tau \bar \nu decays in supersymmetry with R-parity violation (arXiv:1905.08784)

      v1, current

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

      v1, current

    • to be !include-ed as a floating table of contents into relevant entries

      v1, current

    • bare minimum, for the moment just so as to record the basic references

      v1, current

    • a minimum, just for completeness

      v1, current

    • created hyperbolic manifold in order to record a reference on the relation between volumes of hyperbolic 3-folds and their Chern-Simons/Dijkgraaf-Witten invariants by Zickert.

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

      v1, current

    • it’s time to have a contents-table to be !includeed for cross-references in relevant entries

      v1, current

    • starting something, but just a stub for the moment

      v1, current