Linear Gaps Between Degrees for the Polynomial Calculus Modulo Distinct Primes (Abstract)

Samuel R. Buss, Dima Grigoriev, Russell Impagliazzo, Toniann Pitassi

Abstract: Two important algebraic proof systems are the Nullstellensatz system and the polynomial calculus (also called the Grobner system). The Nullstellensatz system is a propositional proof system based on Hilbert's Nullstellensatz, and the polynomial calculus (PC) is a proof system which allows derivations of polynomials, over some field. The complexity of a proof in these systems is measured in terms of the degree of the polynomials used in the proof. The mod p counting principle can be formulated as a set MOD/sub p//sup n/ of constant-degree polynomials expressing the negation of the counting principle. The Tseitin mod p principles, TS/sub n/(p), are translations of the MOD/sub p//sup n/ into the Fourier basis. The present paper gives linear lower bounds on the degree of polynomial calculus refutations of MOD/sub p//sup n/ over p fields of characteristic q /spl ne/ p and over rings Z/sub q/ with q,p relatively prime. These are the first linear lower bounds for the polynomial calculus. As it is well-known to be easy to give constant degree polynomial calculus (and even Nullstellensatz) refutations of the MOD/sub p//sup n/ polynomials over F/sub p/, our results imply that the MOD/sub p//sup n/ polynomials have a linear gap between proof complexity for the polynomial calculus over F/sub p/ and over F/sub q/. We also obtain a linear gap for the polynomial calculus over rings Z/sub p/ and Z/sub q/ where p, q do not have identical prime factors.