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Algebraic and topological K-theory, relations with topology, commutative algebra, and operator algebras

22 votes
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Entering to the K-theory realm

I think that doing algebraic K-theory properly certainly requires a good background on stable homotopy theory, that is to say the homotopy theory of spectra. Unfortunately there are not many textbooks …
Denis Nardin's user avatar
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21 votes
Accepted

Why does K-theory need schemes to be Noetherian?

You don't need the Noetherianness hypothesis to talk about K-theory. But the definition you propose in your question is not suited for the most general case. From a notion of K-theory we want at least …
Denis Nardin's user avatar
  • 16.5k
19 votes
Accepted

Why not $\mathit{KSO}$, $\mathit{KSpin}$, etc.?

I am not sure if this is going to be a real answer to the question. However I believe these observations might be interesting. Let me briefly sketch a way to describe a $G$-structure in (excessively) …
Denis Nardin's user avatar
  • 16.5k
11 votes

Equivalent fomulations of Bott periodicity

The easy way for me to think about this things is via the Yoneda lemma. This works better with reduced $K$-theory. This is defined for a pointed space $X$ as $$ \tilde K^0 (X) := ker(K^0(X)\to K^0(*)) …
Denis Nardin's user avatar
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10 votes
Accepted

Reference request: mod 2 cohomology of periodic KO theory

Ravenel in his Complex Cobordism and Stable Homotopy Groups of Spheres attributes this result to Stong, in Determination of $H^*(BO(k,⋯,∞),Z_2)$ and $H^∗(BU(k,⋯,∞),Z_2)$, but looking at that paper (wh …
Denis Nardin's user avatar
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9 votes
Accepted

Reference request for K-Theory linearization

I claim that for every $A_\infty$-space $A$, there is a canonical $A_\infty$-ring structure on $\Omega^\infty\Sigma^\infty_+A$. First, $\Sigma^\infty_+$ from spaces to spectra is symmetric monoidal. …
Denis Nardin's user avatar
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8 votes

Good reference for topological Hochschild homology

As a first introduction I like these notes by Achim Krause and Thomas Nikolaus. They do require some familiarity with spectra and stable homotopy theory though.
Denis Nardin's user avatar
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8 votes
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On the definition of A-theory

Since the question remains unanswered, let me copy Tom Goodwillie's comment: If you allow finitely dominated instead of finite, it changes only π0. Analogously, in defining K(R) if you use finitely g …
5 votes
Accepted

Which triangulated categories are subcategories of compact objects "somewhere"?

I do not know of an answer for a general triangulated category (non-topological triangulated categories are very unusual), but as soon as you ask for some more structure the thesis follows very quickl …
Denis Nardin's user avatar
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