Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » sci.math.* » sci.math.independent

Topic: Given a set , is there a disjoint set with an arbitrary cardinality?
Replies: 28   Last Post: Dec 4, 2012 5:50 PM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
Carsten Schultz

Posts: 3
Registered: 11/29/12
Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Posted: Dec 3, 2012 11:42 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

Am 03.12.12 17:21, schrieb jaakov:
> On 03.12.2012 16:07, Carsten Schultz wrote:
>> Am 03.12.12 15:21, schrieb jaakov:
>>> Given a set X and a cardinal k, is there a set Y such that card(Y)=k and
>>> X is disjoint from Y?
>>>
>>> Is there a proof of this fact that works without the axiom of regularity
>>> (= axiom of foundation) and does not assume purity of sets?
>>>

>>
>> I am not sure if I understand all of this.
>>
>> Consider the class of all ordinals not in X. This is a well-ordered
>> proper class and hence has an initial segment which is order isomorphic
>> to k. Take that initial segment.
>>
>> hth
>>
>> Carsten

>
> Hi Carsten:
>
> Thank you. To finish this proof, we have to prove that your class, let
> us call it Z, contains an initial segment of cardinality k. However,
> informally speaking, X may hypothetically contain too many ordinals,
> still being a set, such that too few ordinals remain in Z. Could you
> please expand on why Z contains an initial segment of cardinality k?
>


Z has to be a proper class, otherwise the class of all ordinals would
have to be the union of two sets and would therefore be a set.

I you do not like this start with a cardinal number k' greater then
card X + k. Then k'\X is a well-ordered set of cardinality greater then
k and has an initial segment isomorphic to k.







Date Subject Author
12/3/12
Read Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
forbisgaryg@gmail.com
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Aatu Koskensilta
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Carsten Schultz
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Aatu Koskensilta
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Aatu Koskensilta
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Carsten Schultz
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Aatu Koskensilta
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Butch Malahide
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/3/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Butch Malahide
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
forbisgaryg@gmail.com
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
William Elliot
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
forbisgaryg@gmail.com
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
William Elliot
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
William Elliot
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
William Elliot
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Shmuel (Seymour J.) Metz
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
Spammer
12/4/12
Read Re: Given a set , is there a disjoint set with an arbitrary cardinality?
jaakov

Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.