Timeline for Moduli of extensions of modules
Current License: CC BY-SA 4.0
7 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 22, 2022 at 6:50 | history | edited | YCor | CC BY-SA 4.0 |
formatting, expanded title
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| May 19, 2019 at 19:36 | vote | accept | Heinrich Hartmann | ||
| Jul 28, 2010 at 16:52 | answer | added | Arend Bayer | timeline score: 4 | |
| May 22, 2010 at 5:35 | answer | added | Mariano Suárez-Álvarez | timeline score: 4 | |
| May 21, 2010 at 14:21 | answer | added | Peter Arndt | timeline score: 0 | |
| May 21, 2010 at 13:21 | comment | added | Robin Chapman | As you probably know $\mathrm{Ext}^n$ does not parameterise $n$-fold extensions directly but rather certain equivalence classes of them. The equivalence relation is the smallest with the property that $M\to E_1\to E_2\to\cdots \to N$ and $M\to F_1\to F_2\to\cdots \to N$ are equivalent when there's a chain map between them which is the identity on $M$ and $N$. When $n\ge2$ onw can add on an arbitrary module to $E_1$ and $E_2$ and get an equivalent $n$-step extension, so the equivalence classes are proper classes :-) | |
| May 21, 2010 at 13:10 | history | asked | Heinrich Hartmann | CC BY-SA 2.5 |