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Csepp 🌢

@bouncepaw Do they require you to know what that is? Because out textbook specifically said it won't be asked, at least not the precise definition. It did give a simple definition that it's a set constructed from... I think a countably infinite set of countably infinite sets with at most countably infinite set operations, maaybe excluding some specific operations? ...I should look that up...

15 Jan 2023 at 18:03 | Wall-to-wall | Open on merveilles.town
2 comments
bouncepaw 🍄

@csepp no, it won't be asked. I just don't get it, and without understanding it I miss out a lot.

15 Jan 2023 at 18:05 | Open on merveilles.town
Csepp 🌢

@bouncepaw Oh.
Also, oops, was wrong about the kinds of sets it uses:
en.wikipedia.org/wiki/Borel_se

Apparently it uses open or closed sets, which are like open or closed intervals. I supposed the reason they are interchangeable in the definition is that using set difference or union it's easy to convert between closed and open sets.

And using countably infinite operations is similar to thinking about infinite sums in analysis.

@bouncepaw Oh.
Also, oops, was wrong about the kinds of sets it uses:
en.wikipedia.org/wiki/Borel_se

Apparently it uses open or closed sets, which are like open or closed intervals. I supposed the reason they are interchangeable in the definition is that using set difference or union it's easy to convert between closed and open sets.

15 Jan 2023 at 18:09 | Open on merveilles.town
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