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| | Nowhere dense Article, Nowheredense Information (Site not responding. Last check: 2007-11-06) |
 | | For example, the set of rational numbers, as a subset of R has the property that the closure of the interior isempty, but it is not nowhere dense; in fact it is dense in R, which is theopposite notion. |
 | | Every subset of a nowhere dense set is nowhere dense, and the union of finitely many nowhere dense sets is nowhere dense.That is, the nowhere dense sets form an ideal of sets, a suitable notion of negligible set.The union of countably many nowhere dense sets, however, need not be nowheredense. |
 | | For example, if X is the unit interval [0,1], not only is it possible to have a dense set of Lebesgue measure zero (such as the set of rationals), but it is also possible to have a nowheredense set with positive measure. |
| www.anoca.org /set/sets/nowhere_dense.html (381 words) |
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