Sebastian Ordyniak Daniël Paulusma Stefan Szeider Satisfiability of Acyclic and Almost Acyclic CNF Formulas. 84-95 2010 FSTTCS http://dx.doi.org/10.4230/LIPIcs.FSTTCS.2010.84 conf/fsttcs/2010 db/conf/fsttcs/fsttcs2010.html#OrdyniakPS10