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    • Added a reference to the Moerdijk and Weiss’s paper.

      diff, v2, current

    • stub entry, just to satisfy links

      v1, current

    • 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

    • Just some minimum, for completeness, to go in the list of constructions with Sullivan models

      v1, current

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

      v1, current

    • brief category:people-entry for hyperlinking references

      v1, current

    • a stub, just to make links work for the moment

      v1, current

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

      v1, current

    • I’ve started ordinal analysis, mostly because I was beginning to forget a lot of what I once knew, and I had occasion to look into it again.

      I mainly wanted to get the big table in there for future reference, but I tried to say few general remarks as well. I know there’s not much of an npov on ordinal analysis (yet), but it’s certainly of interest concerning strength of type theories for example.

      I may try to fill in more explanations of undefined terms later, but I’m done for today.

    • I was thinking/hoping now that a general approach to perturbative QFT should exist, where all Feynman amplitudes are regarded not as singular distributions on M nM^n, but as smooth differential forms on the FM-compactification of the configuration space of nn points. Mentioning this hunch to Igor Khavkine, he immediately recalled having heard Marko Berghoff speak about developing just that in his thesis Berghoff 14.

      v1, current

    • a bare minimum, just for completeness

      v1, current

    • In the entry spacetime there used to be a subsection on the “hole argument”. It started out with Tim van Beek recalling the “hole paradox” and then continuing with me adding a lengthy discussion, with the result being an organizational mess as far as the poor entry that hosted it was concerned.

      I have now moved that material into its own entry hole paradox, gave it a coherent and concise (I hope) idea-section, and cross-linked with general covariance.

      The section “The hole argument” there is what Tim had originally written, I think, whereas the section Discussion is what I had added back then.

      I am not claiming that that “discussion” of mine is necessarily particular well formulated, but I claim that it gets to the point.

      Looking around I see that one finds the weirdest things being said about the “hole paradox”. For instance the first sentence this article here.

      I am not proposing that we get into this. All I wanted to achieve here is to clean up the poor entry spacetime.

    • I’ve been confused about a search for “pullback lemma” not returning any results, hence this redirect to the proper page

      v1, current

    • I am planning to write a few things about Picard groupoids. For this purpose, I have removed a couple of redirects from Picard 2-group, added a new one which is a bit more precise, and tweaked the beginning of this page slightly. Feel free to edit further; I basically just wished to free up the page Picard groupoid.

    • I gave a short overview of the essay referenced to in the article mysticism. The focus of Russel’s essay is to achieve some compatibility of the approach of Kant’s transcendental aesthetic with geometric developments of his time.

      v1, current

    • Added statement and reference to the original paper

      diff, v2, current

    • Added some comments and updated the table of contents a bit.

      diff, v17, current

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

      Mike Pierce

      v1, current

    • Added a link to a draft version of my chapter for New Spaces in Mathematics and Physics.

      diff, v53, current

    • I added a little discussion of Bourbaki's formalism using the global choice operator choice operator.

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

      v1, current

    • added to coalgebra for an endofunctor the example of the real line as the terminal coalgebra for some endofunctor on Posets.

      There are more such characterizations of the real line, and similar. I can't dig them out right now as I am on a shky connection. But maybe somebody else can. Or I'll do it later.

    • The old webpage link seemed to be dead, so I have replaced it with both the HCM and the HIM links in Bonn.

      diff, v4, current

    • Add missing nullary condition; note unbiased version.

      diff, v2, current

    • starting something, not done yet but need to save

      v1, current

    • splitting this off for ease of hyperlinking. For the moment telegraphic, more later

      v1, current

    • expanded chain homotopy: added the usual non-commuting diagram, a discussion of chain homotopy equivalence and slightly expanded the description in terms of left homotopy

    • am starting something, but not done yet, nothing to be seen here for the moment

      v1, current

    • a stub, just for completeness of the list of proof assistants

      v1, current

    • A long time ago we had a discussion at graph about notions of morphism. I have written an article category of simple graphs which collects some properties of the category under one of those definitions (corresponding better, I think, to graph-theoretic practice).

    • starting something – not done yet, but need to save

      v1, current

    • a bare minimum, just to record the references

      v1, current

    • I just aadded a sentence about Yang-Mills theory to gauge group, but there are some aspects of that article I feel we might want to discuss:

      I don’t think that the statement “gauge groups encoded redundancies” of the mathematical description of the physics is correct. One hears this every now and then, and I suppose the idea is the observation that physical observables have to be in the trivial representation of the gauge group, but there is more to the gauge group than that.

      Notably Yang-Mills theory is a theory of connections on G-principal bundles. No mathematician would ever say that the group G in a G-principal bundle just encodes a redundancy of our descriptins of that bundle. And the reason is because it is true only locally: the thing is that BG={*→g∈G*}\mathbf{B}G = \{* \stackrel{g \in G}{\to} * \} has a single object and hence is connected , but it has higher homotopy groups, and that’s where all the important information encoded by the gauge group sits.

      So I would say that instead of being a redundancy of the description, instead the gauge group of Yang-Mills theory enocedes precisely the homotopy type of its moduli space. This is rather important.

      A different matter are global gauge symmetries such as those that the DHR-theory deals with.

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

      v1, current

    • SC LOL (182.55.198.94) started a page called e, which roughly makes sense.

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