Hans Kleine Büning Xishun Zhao Uwe Bubeck Resolution and Expressiveness of Subclasses of Quantified Boolean Formulas and Circuits. 391-397 2009 SAT http://dx.doi.org/10.1007/978-3-642-02777-2_36 conf/sat/2009 db/conf/sat/sat2009.html#BuningZB09