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Algebraic and topological K-theory, relations with topology, commutative algebra, and operator algebras
2
votes
homotopy groups for good rings
Perhaps an easier approach if you wanted to avoid going into the world of schemes would be to define orthogonal, symplectic, and unitary matrices over $R$ in analogy with the case when $R=\mathbb{C}$. …
8
votes
Representing KO-theory using Clifford algebras
I learned about this in a course taught by Mark Hovey, but we didn't use a book and his lecture notes are not available online. As I recall, you first understand how the signature of a quadratic form …
3
votes
Why is the flat cotorsion pair actually a cotorsion pair?
The proof is given on page 3 of Mark Hovey's paper "Cotorsion Pairs and Model Categories" http://homepages.math.uic.edu/~bshipley/hovey.pdf
After writing "It is not at all obvious that this is a coto …
1
vote
Accepted
Do limits in Waldhausen categories commute with ordinary limits?
Unless I'm misunderstanding your question, the answer is yes. Your second way of defining limits, via "the universal property of a diagram with some arrows in $\mathcal{F}$," is actually a special cas …
2
votes
How to define an equivariant Kasparov's KK-theory map?
Isn't this treated in Claude Schochet's 1992 paper "On Equivariant Kasparov Theory and Spanier-Whitehead Duality"? Also, if you want more references, I'd recommend using Google Scholar to see who cite …
5
votes
If $A$ is a cofibrant commutative dg-algebra over a commutative ring of characteristic $0$, ...
Fernando's answer tells you how to prove the statement directly. Alternatively, if you want a reference, this is proven in Corollary 3.6 of my PhD thesis paper (published in JPAA) Model Structures on …
2
votes
Accepted
Mapping cone and derived tensor product
The comment by skd basically answers your question. I am writing to flesh it out with references, so your question doesn't stay open forever. The derived category of $I$-complete $A$-modules has recen …
13
votes
Short exact sequences every mathematician should know
Short exact sequences form a bridge of sorts between homological algebra and representation theory. For example, Maschke's theorem is the statement that, if $G$ is a finite group and $k$ is a field wh …
41
votes
Short exact sequences every mathematician should know
An example of a short exact sequence satisfying your first desiderata, but one which you probably won't fully understand till you are further along in homological algebra, is the Universal Coefficient …
18
votes
Short exact sequences every mathematician should know
I guess the quintessential example, satisfying your second desiderata, is
$$
0 \rightarrow A \stackrel{f}{\rightarrow} B \rightarrow B/f(A) \rightarrow 0.
$$
For example, if $f = \mu_n: \mathbb{Z} \to …
6
votes
Model structures on the category of unbounded chain complexes
The literature about constructing model structures on abelian categories has grown significantly since Hovey's book came out. In particular, there is now a connection between this process and cotorsio …
6
votes
Accepted
Survey of Algebraic K-Theory Since 1980?
I recommend the Handbook of K-theory. It was published in 2005 and Part II seems to contain what you're looking for.
2
votes
Is there a notion of injective, projective, flat, dimension for a differential graded algebra?
The answer is yes, this theory has been worked out. As a topologist, my favorite reference is Christensen-Hovey "Quillen model structures for relative homological algebra," which works in extreme gene …
5
votes
Is every dg-coalgebra the colimit of its finite dimensional dg-subcoalgebras?
Yes. The category of $\mathbb{Z}$-coalgebras is locally presentable, and objects are filtered colimits of finite dimensional subobjects. See the appendix to Coalgebraic models for combinatorial model …
2
votes
Tensor product of mapping cones
Yes, there is a nice way. The mapping cone $C_i^*$ is the homotopy pushout of $\ast \gets A_i^* \to B_i^*$, and $-\otimes X$ is a monoidal left Quillen functor (symmetric if the underlying ring is com …