Timeline for Uncountable family of infinite subsets with pairwise finite intersections
Current License: CC BY-SA 3.0
15 events
| when toggle format | what | by | license | comment | |
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| Mar 26, 2019 at 0:30 | review | Close votes | |||
| Mar 26, 2019 at 1:33 | |||||
| Feb 26, 2012 at 23:13 | answer | added | Andrej Bauer | timeline score: 13 | |
| Feb 26, 2012 at 23:06 | answer | added | Sean Eberhard | timeline score: 3 | |
| Feb 26, 2012 at 22:20 | history | edited | Goldstern |
logic
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| Feb 24, 2012 at 6:09 | vote | accept | MTS | ||
| Feb 23, 2012 at 22:52 | comment | added | Timothy Chow | This was problem B-4 on the 1989 Putnam. The book by Kedlaya, Poonen, and Vakil gives four solutions, including some of the ones listed here, and mentions that it is also Problem 49 in Newman's book A Problem Seminar. | |
| Feb 23, 2012 at 21:47 | answer | added | Goldstern | timeline score: 5 | |
| Feb 23, 2012 at 20:33 | comment | added | MTS | Goldstern, thanks for that observation. | |
| Feb 23, 2012 at 20:31 | history | edited | MTS | CC BY-SA 3.0 |
Clarified what was meant by "constructive"
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| Feb 23, 2012 at 19:40 | comment | added | Goldstern | If you assume that $X$ is countable (or contains a countable set), then your proof is constructive (or can easily be made constructive), as pointed out by Valerio Caprano. However, the "obvious" fact that every infinite set contains a countably infinite subset may be seen as nonconstructive by some. And indeed, the theorem you stated is not provable in set theory without the axiom of choice (say: in ZF). (Hint: amorphous sets.) | |
| Feb 23, 2012 at 19:06 | answer | added | Tony Huynh | timeline score: 7 | |
| Feb 23, 2012 at 18:47 | answer | added | Todd Eisworth | timeline score: 9 | |
| Feb 23, 2012 at 18:40 | answer | added | Aaron Meyerowitz | timeline score: 4 | |
| Feb 23, 2012 at 18:01 | answer | added | Valerio Capraro | timeline score: 18 | |
| Feb 23, 2012 at 17:41 | history | asked | MTS | CC BY-SA 3.0 |