Timeline for Collection from Replacement in ZFC-extensionality
Current License: CC BY-SA 3.0
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Dec 5, 2020 at 16:03 | vote | accept | Frode Alfson Bjørdal | ||
| Dec 20, 2012 at 13:48 | comment | added | Joel David Hamkins | A related fact would be that one does need the power set axiom to prove collection from replacement. See jdh.hamkins.org/what-is-the-theory-zfc-without-power-set. | |
| Dec 20, 2012 at 12:33 | comment | added | Emil Jeřábek | Hello Frode, welcome to MO! | |
| Dec 20, 2012 at 12:19 | answer | added | Emil Jeřábek | timeline score: 4 | |
| Dec 20, 2012 at 5:30 | comment | added | Mike Shulman | At first when I read this I thought "what the heck?" but then I realized it is kind of an amusing question. Without extensionality, there's not really any way to prove that two sets are equal, and hence not much of any way to construct anything unique. So replacement appears to become kind of useless. (-: | |
| Dec 20, 2012 at 2:57 | comment | added | François G. Dorais | Extensionality is not a schema. (Well, I suppose it is a trivial schema with only one instance.) | |
| Dec 20, 2012 at 2:56 | comment | added | François G. Dorais | Why would you remove extensionality from ZFC? | |
| Dec 20, 2012 at 2:40 | history | asked | Frode Alfson Bjørdal | CC BY-SA 3.0 |