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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.

2 votes

Grade is not equal to injective dimension

https://math.stackexchange.com/questions/3459133/quotient-of-a-local-cohen-macaulay-ring-by-a-minimal-prime gives example of a local Gorenstein ring $R$ with a minimal prime ideal $P$ such that $R/P$ …
Alex's user avatar
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2 votes
0 answers
73 views

From exact triangles in the stable category of maximal Cohen--Macaulay modules to short exac...

Let $R$ be a local Gorenstein ring. Let $\underline{\text{CM}}(R)$ be the stable category of maximal Cohen--Macaulay modules, it is known to carry a triangulated structure. My question is: If $M\to N\ …
Alex's user avatar
  • 480
1 vote
0 answers
84 views

Is $(I(R:_{Q(R)} I))^n$ generated by $(fI)^n$ as $f$ varies over $(R:_{Q(R)} I)$?

Let $(R, \mathfrak m)$ be a Noetherian local domain of dimension $1$ which is not a UFD. Let $Q(R)$ be the fraction field of $R$. If $I\subsetneq \mathfrak m$ is a non-zero, non-principal ideal of $R$ …
Alex's user avatar
  • 480
1 vote
0 answers
53 views

contravariant finiteness and limit closure: is there dual to a result of Crawley-Boevey?

Let $\mathcal A$ be a locally finitely presented category. Theorem 4.2 of https://doi.org/10.1080/00927879408824927 says that given a full additive subcategory $\mathcal D$ of finitely presented objec …
Alex's user avatar
  • 480
2 votes
0 answers
72 views

Sum of Betti numbers and certain short exact sequence of modules of finite length over regul...

Let $N$ be a module of finite length over a regular local ring $R$ of characteristic $0$. Let $M$ be an $R$-module which fits into a short exact sequence $0\to N^{\oplus a}\to M \to N^{\oplus b}\to 0$ …
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  • 480
1 vote
0 answers
78 views

Localization of totally acyclic complex or projective modules remain totally acyclic?

Let $R$ be a commutative Noetherian ring. An acyclic complex $P$ of projective $R$-modules is called totally acyclic if for every projective $R$-module $Q$, the complex Hom$_R(P, Q)$ is also acyclic. …
Alex's user avatar
  • 480
6 votes
2 answers
292 views

If Serre's intersection multiplicity $\chi(R/I, R/J)$ equals $\operatorname{length}_R (R/(I+...

Let $(R,\mathfrak m)$ be a regular local ring. Let $I,J$ be proper ideals of $R$ such that $R/(I+J)$ has finite length i.e. $\sqrt{I+J}=\mathfrak m.$ Since $I+J$ annihilates $\text{Tor}_n^R(R/I, R/J)$ …
Alex's user avatar
  • 480
3 votes
1 answer
120 views

Thick subcategory containment in bounded derived category vs. singularity category

Let $R$ be a commutative Noetherian ring, and $D^b(\operatorname{mod } R)$ the bounded derived category of the abelian category of finitely generated $R$-modules. Let me abbreviate this as $D^b(R)$. C …
Alex's user avatar
  • 480
2 votes
0 answers
91 views

Minimal injective resolution and change of rings

Let $R$ be a commutative Noetherian ring. For an $R$-module $M$, let $0\to E^0_R(M)\to E^1_R(M)\to \ldots $ denote the minimal injective resolution of $M$. I have two questions: (1) If $I$ is an idea …
Alex's user avatar
  • 480
2 votes
1 answer
108 views

Example of non injective module over Noetherian local ring with trivial vanishing against re...

Is there an example of a module $M$ over a commutative Noetherian local ring $(R,\mathfrak m, k)$ such that $\text{Ext}_R^{>0}(k, M)=0$ but $M$ is not an injective $R$-module? I know that for such an …
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  • 480