Andrei A. Krokhin Benoit Larose Maximizing Supermodular Functions on Product Lattices, with Application to Maximum Constraint Satisfaction. 312-328 2008 22 SIAM J. Discrete Math. 1 http://dx.doi.org/10.1137/060669565 db/journals/siamdm/siamdm22.html#KrokhinL08