I have recently started studying Jech's Set Theory on my own and I am stuck on this question.
Prove that $ \cap S $ exists for all $ S \neq \phi $. Where is the assumption $ S \neq \phi $ used in the proof.
I am new to this thing. I was thinking of saying something like
let there be two sets $ A $ and $ B $ so there exists a set $T$ such that $x \in A \cup B \mid P(x)$ where $P(x)$ is $ x \in A \cap B$ by the axiom schema of comprehension. but this doesnt sound right