Ashraf M. Abdelbar Sandra Mitchell Hedetniemi Approximating MAPs for Belief Networks is NP-Hard and Other Theorems. 21-38 1998 102 Artif. Intell. 1 db/journals/ai/ai102.html#AbdelbarH98 http://dx.doi.org/10.1016/S0004-3702(98)00043-5