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Homotopy theory, homological algebra, algebraic treatments of manifolds.

15 votes
1 answer
521 views

What are the advantages of various "models" for the motivic stable homotopy category

People use several distinct models for the motivic stable homotopy category (so, there are some choices for the underlying category and a collection of available model structures). I would like to ask …
Mikhail Bondarko's user avatar
12 votes
1 answer
403 views

Which statements and arguments of Hovey's "Model categories" fail without functorial factori...

I would like to study the homotopy theory of the category of pro-objects over a proper model category $M$. $Pro-M$ is endowed with the strict model structure; it seems that functorial functorizations …
Mikhail Bondarko's user avatar
11 votes
2 answers
725 views

Do there exist "topologically significant" (and not "algebraic") triangulated categories kil...

I have a somewhat vague question: does there exist a prime $p$ and a triangulated category killed by the multiplication by $p$ that would be "interesting for topologists"? This category would probably …
Mikhail Bondarko's user avatar
9 votes
3 answers
2k views

Applications for intersection (co)homology and for the Decomposition Theorem for students?

Which applications of intersection (co)homology and of the (Topological) Decomposition Theorem have most chances to be understood by students?
Mikhail Bondarko's user avatar
9 votes

Chain homotopy: Why du+ud and not du+vd?

Amusingly, I have considered the category of complexes where maps of the form du+vd are killed in: Weight structures vs. $t$-structures; weight filtrations, spectral sequences, and complexes (for mo …
Mikhail Bondarko's user avatar
8 votes
1 answer
1k views

Does one need to sheafify when defining the inverse image of a sheaf with respect to an embe...

This seems to be a rather simple (stupid?:)) question; yet I was not able to find an answer quickly. For a morphism $f:X\to Y$ of schemes (or topological spaces) and an (etale or topological) sheaf $ …
Mikhail Bondarko's user avatar
7 votes
1 answer
497 views

Ring structure for the motivic spectrum/complex that represents singular cohomology?

As the discussion here Is singular cohomology representable by a (Voevodsky's) motivic complex? shows, the singular cohomology of (smooth) complex varieties is represented by a motivic complex (and al …
Mikhail Bondarko's user avatar
7 votes
0 answers
265 views

Do there exist "non-algebraic tensor products" for "algebraic" triangulated categories?

Let us call a triangulated category algebraic if it admits a differential graded enhancement (i.e., an enrichment in complexes of abelian groups). Certainly, there is a notion of a tensor product on d …
Mikhail Bondarko's user avatar
7 votes

A toy example of a tensor triangulated category?

I think that the simplest example is $K(B)$ (the homotopy category of complexes; you can also consider $K^b(B)$) where $B$ is any tensor additive category. Certainly, this example is not independent f …
Mikhail Bondarko's user avatar
6 votes
4 answers
644 views

(Co)homological characterization of homotopy pullbacks

For a commutative square of spaces (of manifolds, or of simplicial sets): $$S=\left(\begin{array}{ccc} A & \to & B \newline \downarrow & & \downarrow \newline C & \to & D\end{array}\right)$$ I am tr …
Mikhail Bondarko's user avatar
6 votes
1 answer
535 views

Exceptional collections of objects in topological triangulated categories?

People often consider exceptional sets of objects (i.e. collections of objects satisfying certain strong orthogonality conditions: $Ext^{l}(P_i,P_j)$ should be zero for $l\neq 0$ + something else) in …
Mikhail Bondarko's user avatar
6 votes
1 answer
641 views

Where can I find basic "computations" of equivariant stable homotopy groups?

I am new to this subject; so please correct me if I will say something wrong or if you don't like my notation. In particular, I don't know whether it is reasonable to consider an infinite group $G$ (s …
Mikhail Bondarko's user avatar
5 votes

Computing fundamental groups and singular cohomology of projective varieties

First we assume that your equations have rational coefficients; if this is not so then you can probably 'approximate' your variety by a variety defined over rationals without changing its topology (th …
Mikhail Bondarko's user avatar
5 votes
2 answers
707 views

On triangulated categories of pro-objects

Which term is used for model categories whose homotopy categories are triangulated? Stable proper model categories? I want $Ho(Pro-M)$ to be triangulated ($Pro-M$ is the category of pro-objects of M) …
Mikhail Bondarko's user avatar
5 votes
1 answer
315 views

Expression of morphisms in motivic homotopy categories in terms of Nisnevich cohomology?

For a perfect field $k$ there is a collection of stable motivic homotopy categories equipped with the corresponding Morel's (homotopy) $t$-structures: $SH^{S^1}(k)$, $SH(k)$, $DA(k)$, and also modules …
Mikhail Bondarko's user avatar

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