Timeline for An ultrafilter and a partition
Current License: CC BY-SA 2.5
3 events
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| Oct 30, 2010 at 7:11 | comment | added | Andreas Blass | As I wrote in my answer (but now with emphasis added), non-principal ultrafilters with the property in the question for all partitions are called "selective" ... The property used as the definition of selectivity in Eisworth's paper is equivalent to this. It immediately implies the definition I gave (partition the pairs $\{a,b\}$ according to whether $a$ and $b$ are in hte same piece of the given partition of $U$), and it immediately follows from the "Ramsey" of Kunen that I cited (by specializing to $n=2$. | |
| Oct 29, 2010 at 9:15 | comment | added | user6976 | @Andreas: Are you sure that these are selective ultrafilters? Here is an article, incidentally communicated by you, where a different definition is given: ams.org/journals/proc/1999-127-10/S0002-9939-99-04835-2/… Note that the question here is not about any partition, but about one particular partition. | |
| Oct 29, 2010 at 6:02 | history | answered | Andreas Blass | CC BY-SA 2.5 |