Talk:Element of Universe

See mu comments in Talk:Unordered Pairs Exist. If $x$ is a set that is proved to exist, and sets are classes, then I can't immediately see the need to duplicate every result that's been proved for sets and prove separately that it also applies to classes. --prime mover 00:33, 15 September 2011 (CDT)


 * You're right. We don't need to duplicate all the results - we only want to duplicate the ones that are specific to proper classes - that is, ones that will hold whether we are talking about sets or proper classes, as this one does.  If $A$ is a set, then the right hand side is satisfied and $A \in U$.  If $A$ is a proper class, then the right side is false. -Andrew Salmon 00:35, 15 September 2011 (CDT)


 * Well that's as may be but you haven't even defined what $U$ is here, let alone $A$. --prime mover 00:41, 15 September 2011 (CDT)


 * ... that's the stuff. Good job. --prime mover 01:40, 15 September 2011 (CDT)