Saturday, 24 June 2017

Dense subset of [0,1] with Lebesgue measure epsilon




We wish to find a Lebesgue measurable subset of [0,1] that is in dense in [0,1] with measure exactly ϵ, where ϵ(0,1). My idea is to let I=(0,ϵ) and let I=Q(ϵ,1). Then set A=II. Is this correct? If so, is there another such set?


Answer



Yes, that works fine. For an open dense set, put intervals of width 2k+100ϵ around the k-th rational number (according to your favorite enumeration of Q(0,1)), adjusted appropriately if the interval doesn't lie in [0,1]. Then lengthen the interval around 1/2 as needed to make up the remaining measure.


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