Vwani P. Roychowdhury Kai-Yeung Siu Alon Orlitsky Thomas Kailath A Geometric Approach to Threshold Circuit Complexity. 97-111 1991 COLT http://portal.acm.org/citation.cfm?id=114836.114846 db/conf/colt/colt1991.html#RoychowdhurySOK91