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On Wed, 21 Aug 2024 07:37:50 -0500, in article <va4n2u$3s0hu$3@dont-email.me>,Often U is used instead of V for the universal set. V is often the
olcott wrote:On 8/21/2024 3:54 AM, Mikko wrote:[...]On 2024-08-20 13:59:42 +0000, olcott said:
On 8/20/2024 5:21 AM, Mikko wrote:
Oh, you blithering imbecile! The universal set V is, by definition,So basically you agreed with me on everything.The set of all sets that do not contain themselves is the Russell setSet theories with an unversal set need to restrictI don't see how. The set of all sets that do not contain
the construction operations more than what is usually considered
reasonable.
themselves simply becomes the set of all sets.
that revealied the inconsistency of the naive set theory. The main
improvment in ZF was the non-existence of this set.
an element of itself. It is a set, and therefore an element of theIf every set has a power set then the univesal has a power set, too,
set of all sets.
By Specification, we can split V into the set of all sets that have
themselves as an element, and its complement, the set of all sets
that are not elements of themselves. Neither of these two sets are
empty.
Do you see where this is going? Or do you need more hand holding?
There are set theories with a universal set, but they also
have restricted Specification. (Or, more commonly, no Axiom of
Specification, but a restricted Comprehension instead.)
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