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# Is the union of any collection of closed sets always closed?

From Mathematics Is A Science

Revision as of 09:25, 3 September 2011 by imported>Tom

Q: Is the union of any collection of closed sets always closed?

A: No.

Why: Try this

$$\left[0, 1 - \frac{1}{n} \right], n = 1, 2, 3, ..,$$