Re: F_sigma

"Arturo Magidin" <magidin@xxxxxxxxxxxxxxxxx> wrote in message
news:del9n2$5vj$1@xxxxxxxxxxxxxxxxxx

> >It says: A set which is a countable union of closed sets is called an
> >F_sigma, **F for closed**, sigma for sum.
> >Looks like I misunderstood F for closed to mean that the F_sigma is
> >closed. It seems this isn't the case, but you can see how I got the
> >impression. Beats me why people don't write better maths
> >books...........
>
>
> It is explaining to you why the terminology "F_sigma". Because it is a
> "sum of closed"; your confusion arose from trying to interpret each
> part of the notation separately.
>
> Beats me why people think you can understand a sentence by examining
> its parts in isolation.

They use the word closed but they don't make it clear whether they are
referring to the F_sigma itself or the fact that the sets making up the
F_sigma are closed. Even you must agree that this ambiguous, or at least
they don't make it clear how the word 'closed' applies.




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