Alexis Maciel Toniann Pitassi On ACC<sup>0</sup>[<i>p<sup>k</sup></i>] Frege Proofs. 720-729 1997 conf/stoc/1997 STOC http://doi.acm.org/10.1145/258533.258669 db/conf/stoc/stoc1997.html#MacielP97