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For questions about the derived categories of various abelian categories and questions regarding the derived category construction itself.

4 votes
0 answers
372 views

Representing $j_*\mathcal{O}_U$ as filtered colimit of perfect complexes

Let $X$ be a quasi-compact and quasi-separated scheme, and $U\subseteq X$ be a quasi-compact open subscheme. Then we can consider $Rj_*\mathcal{O}_U$ the (derived) pushforward of the structure sheaf o …
Denis Nardin's user avatar
  • 16.5k
13 votes
2 answers
1k views

When is the non-negative derived category compactly generated?

This question is strongly related to this question. However it seems to me sufficiently distinct to warrant asking it separately. Let $X$ be a quasi-compact, quasi-separated scheme. When is the ∞- …
Denis Nardin's user avatar
  • 16.5k
15 votes
Accepted

A concrete example of the deficiency of triangulated categories?

Since I have already given a similar answer recently, I don't want to be branded as the "anti-triangular" guy: the formalism of triangulated categories can be useful in certain settings. That said the …
Denis Nardin's user avatar
  • 16.5k
3 votes

Injective resolution for right derived functor

I think you have a little confusion between right and left derived functors. Let me repeat the definition using the language of Kan extensions. In the following for any abelian category $A$ we will wr …
Denis Nardin's user avatar
  • 16.5k
16 votes

Poincare duality on the level of complexes

One way of finding a "fully derived" version of Poincaré duality is Atiyah duality. This says that for any closed manifold $M$ there is an equivalence of spectra (in the sense of algebraic topology) $ …
Denis Nardin's user avatar
  • 16.5k
14 votes
Accepted

Is the derived category of perfect complexes idempotent complete?

The derived category of perfect complexes is idempotent complete, because it is the sub category of compact objects in the derived category of quasi coherent sheaves (which is idempotent complete by t …
Denis Nardin's user avatar
  • 16.5k