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(Co)chain complexes, abelian Categories, (pre)sheaves, (co)homology in various (possibly highly generalized) settings, spectra, derived functors, resolutions, spectral sequences, homotopy categories. Chain complexes in an abelian category form the heart of homological algebra.

11 votes
1 answer
263 views

What are the projective dimensions of big fraction fields?

Let $A$ be an integral domain, $B$ is its fraction field. Can the projective dimension of the $A$-module $B$ be greater than $1$? This surely cannot happen if the spectrum of $A$ is countable (since t …
Mikhail Bondarko's user avatar
4 votes
2 answers
349 views

Are hearts of all $t$-structures on smashing triangulated categories closed with respect to ...

Let $T$ be a triangulated category closed with respect to (small) coproducts, and $t$ be (an arbitrary!) a $t$-structure on $T$. I have noted that the heart $\underline{Ht}$ of $t$ is closed with wit …
Mikhail Bondarko's user avatar
6 votes
1 answer
240 views

For which exact couples do associated spectral sequences degenerate at $E_1$?

It is well known that a bigraded exact couple of objects of an abelian category yields a spectral sequence (cf. https://ncatlab.org/nlab/show/exact+couple#SpectralSequencesFromExactCouples). My questi …
Mikhail Bondarko's user avatar
5 votes
0 answers
518 views

Spectral sequences coming from filtrations (Postnikov systems) in triangulated categories: r...

Let $c^i: M^{\ge i+1}\to M^{\ge i}$ for $i\in \mathbb{Z}$ be an sequence of morphisms in a triangulated category $C$ and assume that $M^{\ge i}$ are equipped with compatible morphisms into an object $ …
Mikhail Bondarko's user avatar
2 votes
Accepted

Is the dual of a compact generator also a compact generator of the derived category of a var...

Let me try to sketch an argument (though I am not quite sure in details). A theorem of Neeman implies that a compact object $M$ in a compactly generated triangulated category $T$ is a generator if an …
Mikhail Bondarko's user avatar
5 votes
2 answers
984 views

On various relations between "additional axioms" for AB4 and Grothendieck abelian categories

Let $A$ be an abelian category that has a generator and satisfies the AB4 axiom. I would like to understand (better) the relations between various additional "restrictions" on $A$. So here is my list …
Mikhail Bondarko's user avatar
5 votes
1 answer
365 views

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

Let $T$ be a small triangulated category. Under which conditions there exists a triangulated category $B$ closed with respect to (small) coproducts such that $T$ fully embedds into the subcategory of …
Mikhail Bondarko's user avatar
5 votes
0 answers
321 views

Do differential objects form triangulated categories?

Let $\mathcal{A}$ be a (fixed) additive category. To a differential object $(A,a)$ for $\mathcal{A}$ (so, $a:A\to A$ and $a^2=0$) one may associate an $\mathcal{A}$-complex $\dots \to A\stackrel{a}{\t …
Mikhail Bondarko's user avatar
3 votes
0 answers
188 views

Can one complete a morphism of commutative triangles to a "commutative cube" in a triangulat...

This question is a continuation of Can one extend a morphism of commutative triangles to a morphism of octahedral diagrams?. I am deeply grateful for the contributions there; they roughly say that gi …
Mikhail Bondarko's user avatar
1 vote
0 answers
70 views

On (universal) additive functors making a given complex contractible: examples?

Let $M=(M^i)$ be a (cohomological) complex of objects of some additive category $A$ (I am mostly interested in "short" complexes; yet one may also consider an unbounded $M$). I am interested in those …
Mikhail Bondarko's user avatar
5 votes
0 answers
225 views

Can triangulated categories be "approximated by countable subcategories" (that are triangula...

For a given (finite) set of (objects and) morphisms $f_i$ in a triangulated category $C$ I am interested in a (non-full!) triangulated subcategory $C'\subset C$ of "small size" that would contain them …
Mikhail Bondarko's user avatar
4 votes
0 answers
162 views

When there exists some "cone" of a morphism of (ind-representable) cohomological functors?

I am interested in cohomological functors from a certain small triangulated category $C$ to abelian groups. The question is: given a tranformation $F\to G$ of two functors of this sort, is it possibl …
Mikhail Bondarko's user avatar
1 vote

A conservative, non faithful functor between triangulated categories

You can start with the derived category of graded polarizable Hodge structures or with the category of Hodge modules (over a complex variety $X$). These categories possess natural weight structures (a …
Mikhail Bondarko's user avatar
6 votes
1 answer
237 views

Left orthogonals to compact objects in triangulated categories: existence and "control"?

Let $C$ be a compactly generated triangulated category. Can it contain a non-zero object $M$ such that there are no non-zero morphisms FROM $M$ into compact objects? I would be grateful for any exampl …
Mikhail Bondarko's user avatar
5 votes
1 answer
833 views

Extension-closed subcategories of triangulated categories as "almost exact" categories

Did anybody study those subcategories of triangulated categories that are closed with respect to "extensions" (in the sense of distinguished triangles; in particular, any such $B$ is additive)? If we …
Mikhail Bondarko's user avatar

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