Timeline for Projective invariants of the plane and cross ratio
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| May 5, 2021 at 14:01 | vote | accept | coudy | ||
| May 4, 2021 at 14:09 | answer | added | Gro-Tsen | timeline score: 3 | |
| May 4, 2021 at 11:49 | history | edited | coudy |
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| May 4, 2021 at 8:37 | history | edited | coudy | CC BY-SA 4.0 |
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| May 4, 2021 at 8:32 | comment | added | coudy | @Polizzi Well, that's part of the question. For five points $A_1$... $A_5$, an explicit formula is to be found in the book of Efimov, higher geometry. The cross ratios involved depend on $A_1$, $A_5$ and one of the intersection points of the lines $A_2A_3$, $A_2A_4$ and $A_3A_4$ with $A_1A_5$. | |
| May 4, 2021 at 8:08 | history | edited | Francesco Polizzi | CC BY-SA 4.0 |
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| May 4, 2021 at 8:05 | comment | added | Francesco Polizzi | Maybe I am missing something, but cross-ratio is usually defined for $4$ points on a line. Here you have $n$ general points in the projective plane, so I expect that non even three of them are collinear. What cross-ratios are you talking about? | |
| May 4, 2021 at 7:58 | history | asked | coudy | CC BY-SA 4.0 |