changed the problem formulation to what I proposed in my prelim: minimize the inversion of preferences. this guarantees tightness of the demand constraints rather than tightness of the supply constraints, which is what we want. a 'large' cost must be attributed to the false arcs. for now I have placed this cost to be the maximum cost divided by minimum unit capacity plus unity. this value is guaranteed to make false arcs a solution of last resort for the problem.