Nowhere Dense Sets With Positive Measure
A nowhere dense set is not necessarily negligible in every sense. For example, if X is the unit interval, 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 nowhere dense set with positive measure.
For one example (a variant of the Cantor set), remove from all dyadic fractions, i.e. fractions of the form a/2n in lowest terms for positive integers a and n, and the intervals around them: (a/2n − 1/22n+1, a/2n + 1/22n+1). Since for each n this removes intervals adding up to at most 1/2n+1, the nowhere dense set remaining after all such intervals have been removed has measure of at least 1/2 (in fact just over 0.535... because of overlaps) and so in a sense represents the majority of the ambient space . This set nowhere dense, as it is closed and has an empty interior: any interval (a, b) is not contained in the set since the dyadic fractions in (a, b) have been removed.
Generalizing this method, one can construct in the unit interval nowhere dense sets of any measure less than 1.
Read more about this topic: Nowhere Dense Set
Famous quotes containing the words dense, sets, positive and/or measure:
“A dense undergrowth of extension cords sustains my upper world of lights, music, and machines of comfort.”
—Mason Cooley (b. 1927)
“And weren’t there special cemetery flowers,
That, once grief sets to growing, grief may rest:
The flowers will go on with grief awhile,
And no one seem neglecting or neglected?
A prudent grief will not despise such aids.”
—Robert Frost (1874–1963)
“I have always had something to live besides a personal life. And I suspected very early that to live merely in an experience of, in an expression of, in a positive delight in the human cliches could be no business of mine.”
—Margaret Anderson (1886–1973)
“What we know partakes in no small measure of the nature of what has so happily been called the unutterable or ineffable, so that any attempt to utter or eff it is doomed to fail, doomed, doomed to fail.”
—Samuel Beckett (1906–1989)