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Topic: G_delta
Replies: 28   Last Post: Jan 26, 2013 3:50 AM

 Messages: [ Previous | Next ]
 David C. Ullrich Posts: 21,553 Registered: 12/6/04
Re: G_delta
Posted: Jan 14, 2013 9:49 AM

On Mon, 14 Jan 2013 00:23:08 -0800 (PST), Butch Malahide
<fred.galvin@gmail.com> wrote:

>On Jan 14, 12:04 am, William Elliot <ma...@panix.com> wrote:
>>
>> In 1st countable spaces, every point p is G_delta.
>> In fact, if every point of a compact Hausdorff space S,
>> is G_delta, then S is 1st countable.

>
>Oh, right, I'd forgotten that.
>

>> Define g:omega_1 -> omega_1 + 1, eta -> eta.
>> Assume S is compact Hausdorff and f in C(omega_1, S).
>>
>> Is there some h in C(omega_1 + 1, S) with f = hg?

>
>Are you just asking whether a continuous function from omega_1 to a
>compact Hausdorff space S can always be extended to a continuous
>function on omega_1 + 1? That sounds like it should be true. I'm not a
>topologist, but I took a course in topology back in 1957-58. I'm not
>sure I remember enough topology to answer a technical question like
>that, but I'll take a stab at it.
>
>First suppose S = [0, 1]. (Gotta walk before you can run.) I believe
>that a continuous real-valued function on omega_1 must be eventually
>constant. (I may even remember how to prove that, but it's late and I
>don't want to do any hard thinking now.) In that case, just map the
>point omega_1 to the same constant, and everything is fine.
>
>Now, can't the result for an arbitrary compact Hausdorff space S be
>derived from the [0, 1] case? Say, by embedding S in a cube, or
>something like that?

Seems right to me. In fact I believe it's right even with the
terminal "or something like that" omitted...

Date Subject Author
1/14/13 William Elliot
1/14/13 Butch Malahide
1/14/13 William Elliot
1/14/13 Butch Malahide
1/14/13 William Elliot
1/14/13 Butch Malahide
1/15/13 William Elliot
1/15/13 Butch Malahide
1/15/13 William Elliot
1/15/13 Butch Malahide
1/16/13 William Elliot
1/15/13 Butch Malahide
1/15/13 Butch Malahide
1/16/13 Butch Malahide
1/18/13 William Elliot
1/18/13 Butch Malahide
1/19/13 William Elliot
1/19/13 Butch Malahide
1/19/13 William Elliot
1/19/13 Butch Malahide
1/20/13 William Elliot
1/20/13 Butch Malahide
1/21/13 William Elliot
1/21/13 Butch Malahide
1/24/13 William Elliot
1/24/13 Butch Malahide
1/26/13 William Elliot
1/14/13 David C. Ullrich
1/14/13 Butch Malahide