Proofs, codes, and polynomial-time reducibilities

We show how to construct proof systems for NP languages where a deterministic polynomial-time verifier can check membership, given any N/sup (2/3)+/spl epsi// bits of an N-bit witness of membership. We also provide a slightly superpolynomial time proof system where the verifier can check membership, given only N/sup (1/2)+/spl epsi// bits of an N-bit witness. These pursuits are motivated by the work of Gal et. al. (1997). In addition, we construct proof systems where a deterministic polynomial-time verifier can check membership, given an N-bit string that agrees with a legitimate witness on just (N/2)+N/sup (4/5)+/spl epsi// bits. Our results and framework have applications for two related areas of research in complexity theory: proof systems for NP, and the relative power of Cook reductions and Karp-Levin type reductions. Our proof techniques are based on algebraic coding theory and small sample space constructions.