Timeline for Descent of singular cohomology
Current License: CC BY-SA 2.5
3 events
| when toggle format | what | by | license | comment | |
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| Jul 4, 2010 at 13:04 | comment | added | user7316 | I see. The excision theorem (or "theorem of small chains") implies that $C^\bullet(U)$ is chain homotopic to $\mathcal{C}^\bullet(U)$ but with U fixed, right? | |
| Jul 4, 2010 at 11:31 | comment | added | Robin Chapman | They aren't sheaves. Consider a covering $(U_i)$ of $X$ and take a $k$-cochain $f_i$ on each $U_i$. If one has a singular $k$-chain $\sigma:\Delta^k\to X$ whose image is not in any of the $U_i$, then its image under the putative cochain on $X$ isn't determined by the $f_i$. | |
| Jul 4, 2010 at 11:03 | history | asked | user7316 | CC BY-SA 2.5 |