A Non-Probabilistic Switching Lemma for the Sipser Function

Abs t r ac t . Valiant [12] showed that the clique function is structurally different than the majority function by establishing the following "switching lemma ~ : Any function f whose set of prime implicants is a large enough subset of the set of cliques (and thus requiring big ~2-circuits), has a large set of prime clauses (i.e., big II2-circuits). As a corollary, an exponential lower bound was obtained for monotone ~II~-circuits computing the clique function. The proof technique is the only non-probabilistic super polynomial lower bound method from the literature. We prove, by a non-probabflistic argument as well, a similar switching lemma for the NCl-complete Sipser function. Using this we then show that a monotone depth-3 (i.e., ~II~ or II~II) circuit computing the Sipser function must have super quasipolynomial size. Moreover, any depth-d quasipolynomial size non-monotone circuit computing the Sipser function has a depth(d 1) gate computing a function with exponentially many both prime implicants and (monotone) prime clauses. These results are obtained by a top-down analysis of the circuits.