A set is called a G delta set if it can be written as the countableintersection of open sets. Any closed set is a G delta set. The complement of a G delta set is called a F sigma set[?]. It is easy to see that any open set is a F sigma set.
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... density is 1,058.4/km² (2,740.4/mi²). There are 5,574 housing units at an average density of 365.4/km² (946.1/mi²). The racial makeup of the town ...