  A recent paper of Jerison and Figalli proved a relationship between the
$H^{1/2}$ norms of smoothed out indicator functions of sets and their
perimeter. We continue this line of investigation and extend it in two ways.
First, we describe a description of the situation with general functions of
bounded variation, and show that a related quantity controls the size of the
jump set. Second, we provide an exact formula in the case of a set of finite
perimeter. Several questions remain and are presented here.
