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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 28, 2013 2:34 PM
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On Thu, 28 Mar 2013 09:24:38 -0700 (PDT), wrote:

>On Thursday, March 28, 2013 3:11:31 PM UTC, Frederick Williams wrote:

>> ...
>> If groups could have classes for the collection of their elements, and
>> if we call such groups "Groups", then we couldn't call the collection of
>> Groups a set or a class, could we?

>I don't see why not. Without further restrictions, the collection of Groups would seem to be too big to be a set, but your Groups could form a class, I would think.
>Classes are allowed to contain other classes after all.

Really? In what version of set theory?

>Of course, we get Russell-type paradoxes if we allow entities to contain themselves, whether the entities be sets or classes.
>Paul Epstein

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