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I know what the union and intersection is, it's just the way they're written together here that's confusing me enter image description here

Asaf Karagila
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John van Zalk
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    You can evaluate out-to-in what everything on the RHS means, and the end result is that $x\in\bigcap_{n=1}^\infty\bigcup_{k=n}^\infty A_k\Leftrightarrow \forall n\ge 1,\exists k\ge n, x\in A_k$. – Sassatelli Giulio Dec 19 '22 at 17:17
  • As long as you know what union and intersection notations mean, I'm afraid this means just what it says. You should elaborate on your confusion. Do you mean to ask, what is the intuition for this, instead of what it its exact meaning? – FShrike Dec 19 '22 at 17:18

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