Tomoyuki Yamakami Andrew Chi-Chih Yao NQP<sub>C</sub> = co-C<sub>=</sub>P. 63-69 1999 71 Inf. Process. Lett. 2 db/journals/ipl/ipl71.html#YamakamiY99 http://dx.doi.org/10.1016/S0020-0190(99)00084-8