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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

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

      v1, current

    • apparently we didn’t have this. Am adding also a diambiguation page

      v1, current

    • I’ve created a page for quaternionic manifolds, linked from quaternion-Kähler page. Basic references and discussion of main definition re Cauchy-Feuter calculus. Comparison to hypercomplex structure.

      v1, current

    • starting something here. For the moment this is just the list of references which I had previously recorded at RR-field tadpole cancellation, now joined by a quick Idea-sentence and a minimal statement of the actual cancellation condition

      v1, current

    • created Einstein manifold

      (for the moment only to record the example of weak G 2G_2-manifolds…)

    • I corrected a couple of wrong claims and added the link to a counter-example

      AG

      diff, v9, current

    • Edit to: GUT by Urs Schreiber at 2018-04-01 01:21:13 UTC.

      Author comments:

      added pointer to textbook account

    • I fixed a broken link to Guy Moore’s lectures

      diff, v9, current

    • added a brief historical comment to Higgs field and added the historical references

    • Created Baire lattice abstracting the Baire category theorem.

      v1, current