Anatoli Degtyarev Robert Nieuwenhuis Andrei Voronkov Stratified resolution. 79-99 2003 36 J. Symb. Comput. 1-2 http://dx.doi.org/10.1016/S0747-7171(03)00036-1 db/journals/jsc/jsc36.html#DegtyarevNV03