List questions from derived-functors

Published on 14 Apr 2026 - 18:08

791

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Understanding $\operatorname{Ext}_R^1(M,A)$ as obstructions to lifting homomorphisms

Published on 13 Apr 2026 - 15:58

90

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Computing Ext for a complex of modules, help with a proof in Stacks Project

Published on 14 Apr 2026 - 6:51

241

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Weibel - Left Derived Functor proof explanation Theorem 2.4.6

Published on 15 Apr 2026 - 15:28

597

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Why can a projective resolution of $A$ be used to calculate $Ext_R^n(A,B)$?

Published on 14 Apr 2026 - 1:47

144

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Exact sequence corresponding to $\bar{\phi} \in \operatorname{Ext}_{\Bbb Z}^1(\Bbb Z_9, \Bbb Z)$ without using Baer sum

Published on 15 Apr 2026 - 4:10

149

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The long exact sequence for left derived functors in Eisenbud's Commutative algebra

Published on 16 Apr 2026 - 7:31

161

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Cech cohomology does not compute étale cohomology - Explanation of an example

Published on 09 Apr 2026 - 22:55

72

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How do a double complex on second quadrant viewed as a single complex?

Published on 09 Apr 2026 - 9:36

197

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About proving a cokernel is not representable

Published on 27 Mar 2026 - 10:24

153

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When is the (great) axiom of Union really needed

Published on 11 Apr 2026 - 1:05

381

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How do you explain why the arguments of $\operatorname{Ext}^1(A,B)$ aren't "backwards"?

Published on 14 Apr 2026 - 14:05

165

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Exercise in Homological Algebra

Published on 11 Apr 2026 - 21:33

51

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About $O_X$-modules?

Published on 14 Apr 2026 - 19:36

308

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Describing $\mathrm{Ext}^1_R (R/J, R/J )$

Published on 16 Apr 2026 - 3:02

List Question

Computing a functor between two categories

Understanding $\operatorname{Ext}_R^1(M,A)$ as obstructions to lifting homomorphisms

Computing Ext for a complex of modules, help with a proof in Stacks Project

Weibel - Left Derived Functor proof explanation Theorem 2.4.6

Why can a projective resolution of $A$ be used to calculate $Ext_R^n(A,B)$?

Exact sequence corresponding to $\bar{\phi} \in \operatorname{Ext}_{\Bbb Z}^1(\Bbb Z_9, \Bbb Z)$ without using Baer sum

The long exact sequence for left derived functors in Eisenbud's Commutative algebra

Cech cohomology does not compute étale cohomology - Explanation of an example

How do a double complex on second quadrant viewed as a single complex?

About proving a cokernel is not representable

When is the (great) axiom of Union really needed

How do you explain why the arguments of $\operatorname{Ext}^1(A,B)$ aren't "backwards"?

Exercise in Homological Algebra

About $O_X$-modules?

Describing $\mathrm{Ext}^1_R (R/J, R/J )$

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