Timeline for How to make an ultranet
Current License: CC BY-SA 2.5
6 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Dec 22, 2010 at 17:44 | vote | accept | Gabriel Furstenheim | ||
| Dec 22, 2010 at 17:34 | answer | added | François G. Dorais | timeline score: 7 | |
| Dec 22, 2010 at 17:16 | comment | added | Pete L. Clark | @François: it seems to me that the paper you cite in your above comment answers the OP's question. Upon reading the question, I myself searched briefly for such a result but didn't find it. Perhaps you should leave this as an actual answer? | |
| Dec 22, 2010 at 16:42 | comment | added | Gabriel Furstenheim | @Dorais. By "constructed" I mean (although I don't how to express it completely formal) a way that gives more insight than just the knowledge of its existence. The same as in Willard: "Explicit constructions of free ultrafilters have never been acomplished" Correct me if I'm wrong: according to that paper there is no hope on finding such a construction only with ZF, as it is consistent that no non-trivial ultrafilter exists at all. | |
| Dec 22, 2010 at 16:13 | comment | added | François G. Dorais | What do you mean by "constructed"? Many ultranets have been "constructed" using the Axiom of Choice. Presumably those are not "constructions" in your sense. There are models of ZF without any nonprincipal ultrafilters - see ams.org/mathscinet-getitem?mr=476510 | |
| Dec 22, 2010 at 13:32 | history | asked | Gabriel Furstenheim | CC BY-SA 2.5 |