Philippe Chapdelaine Miki Hermann Ilka Schnoor Complexity of Default Logic on Generalized Conjunctive Queries. 58-70 2007 conf/lpnmr/2007 LPNMR http://dx.doi.org/10.1007/978-3-540-72200-7_7 db/conf/lpnmr/lpnmr2007.html#ChapdelaineHS07