Timeline for Bijection of proper classes
Current License: CC BY-SA 3.0
3 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Aug 20, 2011 at 17:17 | comment | added | Norman Lewis Perlmutter | Is there an example of a set model of set theory with classes, in which the classes are, externally, not all of the same size? | |
| Jun 18, 2011 at 10:30 | comment | added | Joel David Hamkins | It is consistent with ZFC that there is no global well-ordering, which is equivalent to what you call the limitation of size (since bijections with Ord provide a global well-ordering and conversely). In Goedel-Bernays set theory, one has global well-orderings and hence limitation of size, but not every class need be definable. For example, the classes added by class forcing (which are definitely interesting) are usually not definable. | |
| Jun 18, 2011 at 8:06 | history | answered | Wouter Stekelenburg | CC BY-SA 3.0 |