Re: "Elementary" elements in ZFC.

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Article #1077

#1077

From: Mike Oliver
Date: Mon, 19 Nov 2001 02:08

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John wrote:

> Unfortunately, the meaning of "we will restrict extensionality to
> sets" is hardly clear.  It could mean equi-membered things have to be
> equal IF they are sets; it could mean equi-membered things have to be
> equal ONLY IF they are sets; and it could mean equi-membered things
> have to be equal IF AND ONLY IF they are sets.

This paragraph doesn't make any sense to me.  The only possible
sense of "restrict extensionality to sets" is, if you know two
things are sets and have the same members, you can infer they're
equal.  No assertion at all is made about things that have the
same members but are *not* sets.  Obviously they *can* be
equal, even if they're not sets -- a thing is equal to itself,
whether it's a set or not.

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From: Mike Oliver <oliver@math.ucla.edu>
Newsgroups: sci.logic,sci.math,fa.analytic-philosophy
Subject: Re: "Elementary" elements in ZFC.
Date: Sun, 18 Nov 2001 18:08:00 -0800
Organization: UCLA
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