Michael Bauland Philippe Chapdelaine Nadia Creignou Miki Hermann Heribert Vollmer An Algebraic Approach to the Complexity of Generalized Conjunctive Queries. 30-45 2004 conf/sat/2004lncs SAT (Selected Papers http://dx.doi.org/10.1007/11527695_3 db/conf/sat/sat2004lncs.html#BaulandCCHV04a