Nadia Creignou Heribert Vollmer Boolean Constraint Satisfaction Problems: When Does Post's Lattice Help?. 3-37 2008 Complexity of Constraints http://dx.doi.org/10.1007/978-3-540-92800-3_2 conf/dagstuhl/2008coc db/conf/dagstuhl/coc2008.html#CreignouV08