I'm starting a book on topology and I've come to this come to this confusing statement:(adsbygoogle = window.adsbygoogle || []).push({});

Let A1, A2, ... be subsets of some universal set U.

If the class {A1, A2, ...} is empty, then the intersection of all the Ai is U.

I know that the intersection of empty sets is empty, but I don't quite see how to even think of the intersection of the Ai when {A1, A2, ...} is empty.

Can anyone explain this?

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# Basic question about sets

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