Strong ETH Breaks With Merlin and Arthur: Proof Systems for UNSAT That Beat 2n (With Randomness)
Let Multipoint Arithmetic Circuit Evaluation (MACE) be the task of evaluating an multivariate arithmetic circuit of size s (made of plus and times gates) on s arbitrary inputs. We present a new (probabilistic) proof system for MACE which saves roughly a quadratic factor over the obvious O(s2) time algorithm when the circuit has low degree. There are many corollaries. Of particular interest to this crowd is that there is a proof system for counting SAT assignments to arbitrary Boolean formulas of n variables and 2o(n) size, where the proofs are of length about 2n/2 and the proofs can be verified (using O(n) random bits) in about 2n/2 time with high confidence. In particular, UNSAT for arbitrary Boolean formulas can be verified by proofs of this length and with this running time. This result strongly refutes a "Merlin-Arthur Strong Exponential Time Hypothesis" which had been informally conjectured in the theory community. (Previously appeared in the 2016 Computational Complexity Conference.)