mprv @mprv@social.cleverlibre.org

@freemo I agree, I've seen that construction before.

Reading the statement more carefully it looks like it's constructing a map between a set of sets (X is the set of sets x_i) and the union of those same sets.

Which is perfectly reasonable.

I misread the last symbol as an "equal" rather than a "belongs to". My mistake 😅

@freemo
She is shocked because he's clearly confused about the difference between a set and its elements.
Maybe she's a mathematician 😁