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Mar 8, 2022 at 20:37 comment added user39380 @DanRamras Thanks! the definition of the pairing has been added
Mar 8, 2022 at 20:24 vote accept CommunityBot
Mar 7, 2022 at 16:47 history edited Dan Ramras CC BY-SA 4.0
further corrections as per comments
Mar 7, 2022 at 16:36 comment added Dan Ramras @Tyrone Thanks - I definitely wrote this too early in the morning...
Mar 7, 2022 at 16:19 comment added Tyrone Your formula for $\Sigma M^g$ is not correct (it should be $\Sigma M^g\simeq (\bigvee_{2g}S^2)\vee S^3$). For an explicit homotopy equivalence choose a basis for $H^1M^g$, represented as maps $M^g\rightarrow S^1\simeq K(\mathbb{Z},1)$. Suspend and use the suspension coordinate to add the maps together with the suspension of the pinching map $M^g\rightarrow S^2$. The result is a homology equivalence $\Sigma M^g\simeq\bigvee_{2g} S^2\vee S^3$. (you should also have $[M^g,U]\cong\bigoplus_{2g}\pi_1U$ (in accordance with your first paragraph).
Mar 7, 2022 at 15:35 comment added Dan Ramras The pairing the OP is talking about is described here mathoverflow.net/questions/417368/…
Mar 7, 2022 at 15:30 history edited Dan Ramras CC BY-SA 4.0
removed a mistaken paragraph about ring structure
Mar 7, 2022 at 15:29 comment added Dan Ramras Hmmm... I guess I was thinking of the map $ku\to H\mathbb{Z}$... I was a little worried that this seemed too simple... Anyway, I think from the OP's other recent post, Euler pairing means something else, so I'll remove this part of the answer.
Mar 7, 2022 at 15:28 comment added Lennart Meier One might, however, use the map $KU \to \prod_{i\in \mathbb{Z}} \Sigma^{2i} H\mathbb{Q}$ of ring spectra.
Mar 7, 2022 at 15:24 comment added Denis Nardin What map $H\mathbb{Z}→KU$? I do not think there's such a map of spectra, let alone of ring spectra (if there were, $KU$ would have trivial k-invariants, which they are not).
Mar 7, 2022 at 15:17 history answered Dan Ramras CC BY-SA 4.0