Alexis Maciel Toniann Pitassi Conditional Lower Bound for a System of Constant-Depth Proofs with Modular Connectives. 189-200 2006 conf/lics/2006 LICS http://doi.ieeecomputersociety.org/10.1109/LICS.2006.19 db/conf/lics/lics2006.html#MacielP06