Symmetric clipping proof of transport optimality (source code)

= Symmetric clipping proof of transport optimality
{title2=$u_n=\max(-n,\min(u,n)),\quad v_n=\max(-n,\min(v,n))$}

For a nonnegative cost, simultaneous symmetric clipping preserves feasibility of a pair of <Kantorovich potentials>. On their equality set the clipped sums are nonnegative and increase to the cost. Their bounded integrals are fixed by the marginals, so <monotone convergence theorem> proves optimality without subtracting undefined infinite marginal integrals.