 Finally, formula_100 is (n-1)-rectifiable and the restriction of (n-1)-dimensional Hausdorff measure formula_129 to formula_100 is formula_26, i.e.In other words, up to formula_129-measure zero the reduced boundary formula_100 is the smallest set on which formula_21 is supported.From the definition of the vector Radon measure formula_21 and from the properties of the perimeter, the following formula holds true