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Topic: Compactification
Replies: 15   Last Post: Mar 17, 2013 6:11 AM

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 fom Posts: 1,968 Registered: 12/4/12
Re: Compactification
Posted: Mar 17, 2013 6:08 AM

On 12/11/2012 10:13 PM, William Elliot wrote:
> (h,Y is a (Hausdorff) compactification of X when h:X -> Y is an embedding,
> Y is a compact (Hausdorff) space and h(X) is a dense subset of Y.
>
> Why the extra luggage of the embedding for the definition of
> compactification? Why isn't the definition simply
> Y is a compactification of X when there's some
> embedding h:X -> Y for which h(X) is a dense subset of Y?
>
> I see no advantage to the first definition. The second definition
> has the advantage of being simpler and more intuitive. So why is
> it that the first is used in preference to the second which I've
> seen used only in regards to one point compactifications?
>

What if one can describe another mapping g:X->Y
for which the image g(X) is not dense in Y?

Perhaps the language for one-point compactification
reflects the fact that the topology of the resulting
compact space arises from the existing open and compact
sets from the given locally compact Hausdorff space.

It is intrinsically well-defined.

I am sure others will give you more useful opinions.

Date Subject Author
12/11/12 William Elliot
12/11/12 magidin@math.berkeley.edu
12/13/12 William Elliot
12/13/12 magidin@math.berkeley.edu
12/14/12 William Elliot
12/14/12 magidin@math.berkeley.edu
12/14/12 David Hartley
12/14/12 Butch Malahide
12/15/12 David Hartley
12/12/12 Shmuel (Seymour J.) Metz
12/13/12 William Elliot
12/13/12 Shmuel (Seymour J.) Metz
12/12/12 David C. Ullrich
12/13/12 William Elliot
3/17/13 fom
3/17/13 fom