Timeline for Flatness over non-reduced schemes : no geometric characterisation
Current License: CC BY-SA 3.0
13 events
| when toggle format | what | by | license | comment | |
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| Apr 13, 2017 at 12:58 | history | edited | CommunityBot |
replaced http://mathoverflow.net/ with https://mathoverflow.net/
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| Oct 24, 2011 at 14:39 | comment | added | Julien Puydt | I can't help but wonder why there is both "Display name" and "Real name"... and one is hidden anyway, but now I changed both to the same. | |
| Oct 24, 2011 at 11:49 | comment | added | Sándor Kovács | Just as you, I did not mean to offend you (and I tried to make that clear). Your real name is not displayed to anyone else, but it is an understandable mistake. | |
| Oct 24, 2011 at 10:17 | comment | added | Julien Puydt | What annoys me most is that when I started my comment with "@..." I knew I needed to be careful -- and that wasn't enough. My real name is in my profile.... what I thought would be a login name ended up being the displayed name. Perhaps I should change that... | |
| Oct 23, 2011 at 19:44 | comment | added | Sándor Kovács | p.s.: It also makes a difference when you make comments under your real name (like Donu and I). There is a tendency to be more careless when one is posting under a pseudonym. Cheers! | |
| Oct 23, 2011 at 19:42 | comment | added | Sándor Kovács | @Snark: Your comment does read a little aggressive. I am sure you did not mean it that way, but it's good to try to think about it how it might sound to someone else. Then again, I have made the same mistake a number of times and probably will again... | |
| Oct 23, 2011 at 17:12 | comment | added | Donu Arapura | The internet seems to be an imperfect medium for communication. Thank you for clarifying. | |
| Oct 23, 2011 at 16:39 | comment | added | Julien Puydt | @Donu Arapura: you sound like you feel offended ; that was definitely not the goal : I'm sorry if my comment went through as this. I'm asking the question precisely because I have the impression there was something deep I was missing. In fact, I'm not exactly sure what they mean by "geometric property"... it must not be about topology (or they would have used that word), it must not be purely algebraic (geometry is often opposed to algebra... as two sides of the same coin). | |
| Oct 23, 2011 at 15:52 | comment | added | Donu Arapura | I'm aware of both of those facts. It's possible you're asking the wrong people. | |
| Oct 23, 2011 at 14:48 | comment | added | Julien Puydt | @Donu Arapura: counter-examples will tell "This isn't a geometric characterisation of flatness" ; they won't give "There is no geometric characterisation of flatness"... (And I did mention they were referencing EGA IV(2) 6.9.1) | |
| Oct 23, 2011 at 14:28 | comment | added | Donu Arapura | To complement Sándor's answer, the "identity map" $X_{red}\to X$ is generally not flat. In fact generic flatness (EGA IV 6.9.1) will fail for the simplest example $Spec k\to Spec k[\epsilon]/(\epsilon^2)$. | |
| Oct 23, 2011 at 14:05 | answer | added | Sándor Kovács | timeline score: 2 | |
| Oct 23, 2011 at 13:58 | history | asked | Julien Puydt | CC BY-SA 3.0 |