Re: elaboration Re: Cantor's Diagonal

2007-11-22 Thread Bruno Marchal


Le 22-nov.-07, à 07:19, Barry Brent a écrit :


 The reason it isn't a bijection (of a denumerable set with the set of
 binary sequences):  the  pre-image (the left side of your map) isn't
 a set--you've imposed an ordering.  Sets, qua sets, don't have
 orderings.  Orderings are extra.  (I'm not a specialist on this stuff
 but I think Bruno, for example, will back me up.)  It must be the
 case that you won't let us identify the left side, for example, with
 {omega, 0, 1, 2, ... }, will you? For if you did, it would fall under
 Cantor's argument.


I agree.
Presently, I prefer not talking too much on the ordinals, because it 
could be confusing for many.  More later ...

Bruno



http://iridia.ulb.ac.be/~marchal/


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elaboration Re: Cantor's Diagonal

2007-11-21 Thread Barry Brent

The reason it isn't a bijection (of a denumerable set with the set of  
binary sequences):  the  pre-image (the left side of your map) isn't  
a set--you've imposed an ordering.  Sets, qua sets, don't have  
orderings.  Orderings are extra.  (I'm not a specialist on this stuff  
but I think Bruno, for example, will back me up.)  It must be the  
case that you won't let us identify the left side, for example, with  
{omega, 0, 1, 2, ... }, will you? For if you did, it would fall under  
Cantor's argument.

Barry

On Nov 21, 2007, at 10:33 AM, Torgny Tholerus wrote:

 Bruno Marchal skrev:
 Le 20-nov.-07, à 23:39, Barry Brent wrote :
 You're saying that, just because you can *write down* the missing  
 sequence (at the beginning, middle or anywhere else in the list),  
 it follows that there *is* no missing sequence. Looks pretty  
 wrong to me. Cantor's proof disqualifies any candidate  
 enumeration. You respond by saying, well, here's another  
 candidate! But Cantor's procedure disqualified *any*, repeat  
 *any* candidate enumeration. Barry Brent
 Torgny, I do agree with Barry. Any bijection leads to a  
 contradiction, even in some effective way, and that is enough (for  
 a classical logician).

 What do you think of this proof?:

 Let us have the bijection:

 0  {0,0,0,0,0,0,0,...}
 1  {1,0,0,0,0,0,0,...}
 2  {0,1,0,0,0,0,0,...}
 3  {1,1,0,0,0,0,0,...}
 4  {0,0,1,0,0,0,0,...}
 5  {1,0,1,0,0,0,0,...}
 6  {0,1,1,0,0,0,0,...}
 7  {1,1,1,0,0,0,0,...}
 8  {0,0,0,1,0,0,0,...}
 ...
 omega --- {1,1,1,1,1,1,1,...}

 What do we get if we apply Cantor's Diagonal to this?

 -- 
 Torgny

 

Dr. Barry Brent
[EMAIL PROTECTED]
http://home.earthlink.net/~barryb0/




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