“…Let us now select a point a = (a 1 , a 2 ) such that a 1 ∈ A, a 2 ∈ B, and let us define the auxiliary BV functions ω(z) = M (z − a) + u(a), and ψ(z) = u(z) − ω(z). For every x ∈ A, y ∈ (−3r, 3r), then, since ψ(a) = 0 we have 4) and the obvious modification of the argument implies that the estimate holds true also for x ∈ (−3r, 3r), y ∈ B. Let now (x, y) be any point in Q(c, 2r); thanks to (4.3) we can select x − < x < x + and y − < y < y + such that x ± ∈ A, y ± ∈ B, and |x + − x − | < r/R, |y + − y − | < r/R.…”