[234]Prerequisites:[06P]↺↻,[231]↺↻.If \((X,≤)\) a filtering set, \(Y⊆ X\) is cofinal, and \(U⊆ X\) is a neighborhood of \(∞\) in \(X\), show that \(U∩ Y\) is a neighborhood of \(∞\) in \(Y\).
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