Eli Ben-Sasson Prahladh Harsha Sofya Raskhodnikova Some 3CNF Properties Are Hard to Test. 1-21 2005 35 SIAM J. Comput. 1 http://epubs.siam.org/SICOMP/volume-35/art_44544.html db/journals/siamcomp/siamcomp35.html#Ben-SassonHR05