A Satisfiability Algorithm for AC

We consider the problem of efficiently enumerating the satisfying assignments to AC circuits. We give a zeroerror randomized algorithm which takes an AC circuit as input and constructs a set of restrictions which partitions {0, 1} so that under each restriction the value of the circuit is constant. Let d denote the depth of the circuit and cn denote the number of gates. This algorithm runs in time |C|2n(1−μc,d) where |C| is the size of the circuit for μc,d ≥ 1/O[lg c + d lg d]d−1 with probability at least 1− 2−n. As a result, we get improved exponential time algorithms for AC circuit satisfiability and for counting solutions. In addition, we get an improved bound on the correlation of AC circuits with parity. As an important component of our analysis, we extend the H̊astad Switching Lemma to handle multiple k-cnfs and k-dnfs.