# Total Search Problems in Bounded Arithmetic and Improved Witnessing

## Jean Razafindrakoto

(Swansea University)

We define a new class of total search problems as a subclass of Megiddo and Papadimitriou's class of total $\NP$ search problems, in which solutions are verifiable in $\AC^0$. We denote this class $\forall\exists\AC^0$. We show that all total $\NP$ search problems are equivalent wrt. $\AC^0$-many-one reductions to search problems in $\forall\exists\AC^0$. Furthermore, we show that $\forall\exists\AC^0$ contains well-known problems such as the Stable Marriage and the Maximal

Independent Set problems. We introduce the class of Inflationary Iteration problems in $\forall\exists\AC^0$ and show that it characterizes the provably total $\NP$ search problems of the bounded arithmetic theory corresponding to polynomial-time. Cook and Nguyen introduced a generic way of defining a bounded arithmetic theory $\VC$ for complexity classes $\C$ which can be obtained using a complete problem. For such $C$ we will define a new class $\KPT[C]$ of $\forall\exists\AC^0$ search problems based on Student-Teacher games in which the student has computing power limited to $\AC^0$. We prove that $\KPT[C]$ characterizes the provably total $\NP$ search problems of the bounded arithmetic theory corresponding to $\C$. All our characterizations are obtained via "new-style" witnessing theorems, where reductions are provable in a theory corresponding to $\AC^0$.

**Thursday 29th June 2017, 16:00**

Board Room (Faraday 314)

Department of Computer Science