Timeline for Extending an automorphism from a sub-algebra to the algebra
Current License: CC BY-SA 3.0
7 events
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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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| Mar 26, 2017 at 6:08 | comment | added | R. van Dobben de Bruyn | @YCor: ah, very good! I guess I was tacitly assuming $\operatorname{char}(k) = 0$, because that was a running assumption in the original post. | |
| Mar 26, 2017 at 2:02 | comment | added | Lubin | “Almost never”. Exactly the words I used in the blurb advertising my talk at Brown Wednesday last. | |
| Mar 26, 2017 at 1:17 | comment | added | YCor | In the first example you have to assume $k$ not of char 2 since otherwise $x^2+1$ is a square and indeed in this case there is an extension of the automorphism. | |
| Mar 25, 2017 at 22:45 | comment | added | user237522 | Nice answer, thanks! also thanks to @YCor for all his nice counter-examples (one of his counter-examples appears in the answer). | |
| Mar 25, 2017 at 22:04 | vote | accept | user237522 | ||
| Mar 25, 2017 at 21:52 | history | answered | R. van Dobben de Bruyn | CC BY-SA 3.0 |