ON THE POWER OF INTERACTION.

Abstract

A hierarchy of probabilistic complexity classes generalizing NP has recently emerged. The IP hierarchy is defined through the notion of an interactive proof system, in which an all powerful prover tries to convince a probabilistic polynomial-time verifier that a string x is in a language L. The verifier tosses coins and exchanges messages back and forth with the prover before he decides whether to accept x; the verifier may erroneously accept or reject x with small probability. Evidence is given here that interactive proof systems with an unbounded number of interactions may be more powerful than interactive proof systems with a bounded number of interactions.