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( pdf ) On formula complexity for products of Boolean functions //
Diskretn. Anal. Issled. Oper. Ser. 1. 9(1): 84-94 (2002), in Russian [links: mathnet , Zbl 1009.68056 , ams ] Abstract: Let $f(x_1,\dots,x_n)$ and $g(x_1,\dots,x_m)$ be Boolean functions.