 On the other hand, a set may have topological dimension less than "n" and have positive "n"-dimensional Lebesgue measure.An example of this is the Smith–Volterra–Cantor set which has topological dimension 0 yet has positive 1-dimensional Lebesgue measure.In order to show that a given set "A" is Lebesgue-measurable, one usually tries to find a "nicer" set "B" which differs from "A" only by a null set (in the sense that the symmetric difference ("A" − "B") formula_53("B" − "A") is a null set) and then show that "B" can be generated using countable unions and intersections from open or closed sets.