Feasibility of Primality in Bounded Arithmetic

Abstract

We prove the correctness of the AKS algorithm \cite{AKS} within the bounded arithmetic theory $T^{count}_2$ or, equivalently, the first-order consequences of the theory $VTC^0$ expanded by the smash function, which we denote by $VTC^0_2$. Our approach initially demonstrates the correctness within the theory $S^1_2 + iWPHP$ augmented by two algebraic axioms and then show that they are provable in $VTC^0_2$. The two axioms are: a generalized version of Fermat's Little Theorem and an axiom adding a new function symbol which injectively maps roots of polynomials over a definable finite field to numbers bounded by the degree of the given polynomial. To obtain our main result, we also give new formalizations of parts of number theory and algebra: $\bullet$ In $PV_1$: We formalize Legendre's Formula on the prime factorization of $n!$, key properties of the Combinatorial Number System and the existence of cyclotomic polynomials over the finite fields $\mathbb{Z}/p$. $\bullet$ In $S^1_2$: We prove the inequality $lcm(1,\dots, 2n) \geq 2^n$. $\bullet$ In $VTC^0$: We verify the correctness of the Kung--Sieveking algorithm for polynomial division.