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    • Someone started a page called probability amplitudes but with a single word. I have changed that to say the page is empty. (which of course it is not!) as I did not feel competent to write even a stub on that topic.

    • created models in presheaf toposes with the statement of the fact that T-models in presheaves are presheaves of T-models, at least for T a geometric theory.

      Added a pointer to this from the corresponding discussion at group object.

    • There was some misnumbering (sometimes off by 1, sometimes reversed) at homotopy group#truncconn, which hopefully I've fixed.

    • added to odd line a brief remark on the nature of its automorphism super-group and the consequences, also added some relevant references.

      (I feel like I had added this statement to the nnLab elsewhere already long time ago, but can’t find it now.)

    • I was fixing some Spam at generator and noticed that Grothendieck category has a link to generator, but shouldn’t this be to separator? I have fixed it so that the term generator in Grothendieck category links to separator.

      I tried to clear up some formatting problems / typos at separator. (There is a query near the bottom of the page that seems to still be unanswered.) Can someone glance at the entry to check my reformatting is right as I was on autopilot when doing it!

    • Just now I needed a definition and discussion of term algebra for the new entry on Lindenbaum-Tarski algebra. I noted we have Lindenbaum algebra in several places with no explanation. I am no logician and have very few logic books available. Are these the same and what generality should be used for the term algebra.

      I also looked at the entry on Boolean algebra and was a bit surprised to find there was no elementary algebraic version given. This is the (for dummies) version perhaps, but seeing one of the usual algebraic description and examples (although these are in the Wikipedia page I’m sure) might enable the ideas about Heyting algebras, lattices, etc., there to be more useful. I’m not sure what level to pitch any additions to that entry, any ideas or thoughts anyone?

    • I am going to rewrite a part of the Baer sum, the section “On short exact sequences”, partly following S. MacLane, Homology, 1963 (he does the version for extensions of RR-modules). I am not fully understanding and would like to discuss the issue, but I think the current notation is a bit hiding. So here is the version of the section before my update, so it can be reversed if somebody not happy:

      For 0→A→G^ i→G→00 \to A \to \hat G_{i} \to G \to 0 for i=1,2i = 1,2 two short exact sequences of abelian groups, their Baer sum is

      G^ 1+G^ 2≔+ *Δ *G^ 1×G^ 2 \hat G_1 + \hat G_2 \coloneqq +_* \Delta^* \hat G_1 \times \hat G_2

      The first step forms the pullback of the short exact sequence along rhe diagonal on GG:

      A⊕A → A⊕A ↓ ↓ Δ *(G^ 1⊕G^ 2) → G^ 1⊕G^ 2 ↓ ↓ G →Δ G G⊕G \array{ A \oplus A &\to& A \oplus A \\ \downarrow && \downarrow \\ \Delta^* (\hat G_1 \oplus \hat G_2) &\to& \hat G_1 \oplus \hat G_2 \\ \downarrow && \downarrow \\ G &\stackrel{\Delta_G}{\to}& G\oplus G }

      The second forms the pushout along the addition map on AA:

      A⊕A →+ A ↓ ↓ Δ *(G^ 1⊕G^ 2) → + *Δ *(G^ 1⊕G^ 2) ↓ ↓ G → G \array{ A \oplus A &\stackrel{+}{\to}& A \\ \downarrow && \downarrow \\ \Delta^* (\hat G_1 \oplus \hat G_2) &\to& +_* \Delta^*(\hat G_1 \oplus \hat G_2) \\ \downarrow && \downarrow \\ G &\to& G }

    • I’ve changed Postnikov system definition 2

      the part saying

      “The map X→im n(f)X \to im_n(f) induces an epimorphism on connected components”

      to

      “The map X→im n(f)X \to im_n(f) induces an epimorphism on homotopy groups in degree n−1n-1”.

      This was a small issue that confused me.

    • I've seen two meanings for this term, and they are both at limit point, along with a family of other terms for various arity classes.

    • I saw that one of the classical arity classes didn't have a name, so I named it ‘subunary’.

    • I just deleted the query

      Did you do these edits attributed to ’Ronald null Brown’? —Toby

      at Ronnie Brown.

    • added an entry for the Kan Thurston Theorem.
      http://ncatlab.org/nlab/show/Kan-Thurston+Theorem

    • A few grad students and I are starting a reading group on the Firewall problem and related aspects, so I’ve created a page in the nLab with a bunch of relevant papers:

      (not yet a complete list.)

      The goal will be to develop the page into a introduction to the problem, and the resolutions proposed, etc.

    • you all knew it was about to happen, and now it did: I have created a table-of-contents page for inclusion as “floating TOC” in the relevant entries:

    • added to limit in a quasi-category (in the Properties-section) more details on how the definition in terms of over over-categories is equivalent to the one in terms of homs. But still not done.

    • added the definition of relative (infinity,1)-limit, because I need to point to it from elsewhere.

      (Somehow the cache bug, or a new version of it kicked in, and there is now also relative (∞,1)-limit, which I won’t try to fight with just right now…)

    • Someone (probably in Gottingen) created a slideshow page. I renamed it Slideshow sandbox and removed its contents which were

      www.math.columbia.edu/~woit/notes16.pdf

      That was the old name as well.

    • Euclid (Εὐκλείδης) was the ancient Greek version of Bourbaki.

    • Urs created submersion and I added a little more. Still a bit stubby, though.

    • I have added the Nadler’s today’s paper at Waldhausen S-construction. It would perhaps make sense to quote it in some more entries.

    • Someone has made a change to the page on Aleksandr Aleksandrov, but there are some characters in the Cyrillic form of his name that are not coming out. Does anyone know how to fix this?

    • am starting to make some basic notes on Gysin/Umkehr/pushforward maps in KK-theory, currently in fiber integration in the section In KK-theory. But still with some gaps.

    • started stub for Chow group

      hoping I got this right...

    • I created the page

      h-topology

      (just a stub right now).

    • Started smooth loop space, initially just a stub. Partly to contain some bits of general theory relating to which smooth paths do I use (davidroberts) and partly to start transferring some notes on the differential topology of loop spaces over to the nLab.

      In looking for somewhere to graft it on to the current nLab tree, I encountered loop space object. It seemed to me that the smooth loop space is not a loop space object, so I commented as such (thus also creating the link to smooth loop space which was my real intent). Someone who knows these things better than I do should check this.

    • created product law, since I wanted to be able to link to it…

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