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

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Shmuel (Seymour J.) Metz

Posts: 3,309
Registered: 12/4/04
Re: Using classes instead of sets
Posted: Mar 29, 2013 6:24 PM
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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.

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