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    • Kochmann should be Kochman:

      Presumably #Kochmann96 should be corrected to #Kochman96, but I haven’t changed this as I’m afraid I might break things.


      diff, v34, current

    • Attempt at making a page about defunctionalization. My first new page on nlab, I hope there are no faux pas’s. I noticed the resemblance to the adjoint functor theorem a while back, and several people seemed to find it interesting, so I thought I’d make a page.

      v1, current

    • I filled in a bit on the Wightman axioms. I also have a query there about adding an "axiom" environment to the LaTeX/CSS style sheets of nLab. I don't know how to do it on nLab but an axiom environment seems like it might be useful.
    • “Covariant presheaf” seems to be a more widely-used name than “copresheaf”, so it’s useful to document it here.

      diff, v4, current

    • created a minimum at function monad (aka “reader monad”, “environment monad”)

    • Create page, add some initial references. Referenced from the ’category theory’ page.

      v1, current

    • 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

    • Stub for associative n-categories.

      v1, current

    • Jamie Vicary is kindly adding information to the nnLab on the higher-category-theory-proof-assistant that he and collaborators are developing, at:

      I have added a few more hyperlinks to related nLab entries.

      And I have changed the page name from lower case “globular” to upper case “Globular” to fit our conventions on entry titles.

      Currently, lower case “globular” still redirects to the entry. But if anyone has links to the lower case version from elsewhere, please consider changing them, for eventually the lower case “globular” really ought to go to a page that disambiguates all sorts of globular-related entries on the nLab, such as globe and globular set, etc.

    • Created stub for Spin group. Made a mess of explaining why it is so named.

      -David Roberts
    • I am splitting off an entry classification of finite rotation groups from ADE classification in order to collect statements and references specific to the classification of finite subgroups of SO(3)SO(3) and SU(2)SU(2).

      Is there a canonical reference for the proof of the classification statement? I find lots of lecture notes that give the proof, but all of them without citing sources or original publications of proofs.

      v1, current

    • Forgot to mention that I started something on Coxeter group. A lot of it is examples, particularly finite reflection groups (where the classification was effectively stated). If someone knows how to draw Coxeter diagrams, those would be great to include.

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

      v1, current

    • added to icosahedral group discussion of the distinction of definitions as one moves up the Whitehead tower of O(3)O(3)

      String SU(2) 2I Spin(3)=SU(2) IA 5 SO(3) I hA 5×/2 O(3) \array{ \mathcal{I} &\hookrightarrow& String_{SU(2)} \\ \downarrow && \downarrow \\ 2 I &\hookrightarrow & Spin(3) = SU(2) \\ \downarrow && \downarrow \\ I \simeq A_5 &\hookrightarrow& SO(3) \\ \downarrow && \downarrow \\ I_h \simeq A_5\times \mathbb{Z}/2 &\hookrightarrow & O(3) }

      [edit: added analogous discussion to octahedral group and icosahedral group ]

    • a stub, trying to bring in infrastructure for discussion of the finite subgroups of O(5)O(5)

      v1, current

    • a stub, am trying to bring into place some infrastructure for discussion of the finite subgroups of O(5)O(5)

      v1, current

    • starting a stub, for the moment just collecting references.

      Which finite subgroup of SO(4)SO(4) corresponds to the 120-cell?

      v1, current

    • Created opetopic type theory with a bit of explanation based on what I understood based on what Eric Finster explained and demonstrated to me today.

      This is the most remarkable thing.

      I have added pointers to his talk slides and to his online opetopic type system, but I am afraid unguided exposition to either does not reveal at all the utmost profoundness of what Eric made me see when he explained and demonstrated OTT to me on his notebook. I hope he finds time and a way to communicate this insight.

    • created stub for étale morphism of E-∞ rings in order to record the theorem of essential uniqueness of lifts of étale morphism from underlying commutative rings to E E_\infty-rings (which is crucial for the characterization of the moduli stack of derived elliptic curves, and I have cross-linked with that). But otherwise no content yet, due to lack of leisure.