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Is the intersection of any collection of open sets always open?
From Mathematics Is A Science
Revision as of 09:24, 3 September 2011 by imported>Tom
Q: Is the intersection of any collection of open sets always open?
A: No.
Why: Try this
$$(-\frac{1}{n}, \frac{1}{n}), n = 1, 2, 3, ..,$$
Under what circumstances is it open? Answer.
