Richard Beigel John Gill Counting Classes: Thresholds, Parity, Mods, and Fewness. 3-23 1992 103 Theor. Comput. Sci. 1 db/journals/tcs/tcs103.html#BeigelG92 http://dx.doi.org/10.1016/0304-3975(92)90084-S