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Topic: Using classes instead of sets
Replies: 26   Last Post: Apr 1, 2013 8:04 PM

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David C. Ullrich

Posts: 21,553
Registered: 12/6/04
Re: Using classes instead of sets
Posted: Mar 30, 2013 10:35 AM
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On Fri, 29 Mar 2013 18:24:47 -0400, Shmuel (Seymour J.) Metz
<spamtrap@library.lspace.org.invalid> wrote:

>In <f8ral8lndkanp4gd70pu1fmblq4g912o74@4ax.com>, on 03/29/2013
> at 06:07 AM, quasi <quasi@null.set> said:
>

>>There are certain concepts for which sets are inadequate and classes
>>come to the rescue. For example, we need the class concept if we
>>want to define an equivalence on the collection of all groups, since
>>that collection is not a set.

>
>There's no such set in ZFC, but there are set theories in which it
>exists aqnd is a set.


Oh? For example?







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