SAS

Abstract

The "first part" of Toda's theorem states that every language in the polynomial hierarchy is probabilistically reducible to a language in $\oplus P$. The result also holds for the closure of the polynomial hierarchy under a parity quantifier. We use Jerabek's framework for approximate counting to show that this part of Toda's theorem is provable in a relatively weak fragment of bounded arithmetic with a parity quantifier. We discuss the significance of the relativized version of this result for bounded depth propositional proof systems with parity gates. Joint work with Sam Buss and Konrad Zdanowski.