We apply our new hitting set enumeration algorithm to solve the sudoku
minimum number of clues problem, which is the following question: What is the
smallest number of clues (givens) that a sudoku puzzle may have? It was
conjectured that the answer is 17. We have performed an exhaustive search for a
16-clue sudoku puzzle, and we did not find one, thereby proving that the answer
is indeed 17. This article describes our method and the actual search.
In this article, we give a complete description of the characteristic
polynomials of supersingular abelian varieties over finite fields. We list them
for the dimensions upto 7.
We study the intersection of two particular Fermat hypersurfaces in
$\mathbb{P}^3$ over a finite field.
Using the Kani-Rosen decomposition we study arithmetic properties of this
curve in terms of its quotients. Explicit computation of the quotients is done
using a Gr\"obner basis algorithm. We also study the $p$-rank, zeta function
and number of rational points. We make a conjecture about the Jacobian of the
genus 2 quotient, which we show is $(4,4)$-split.
We prove a conjecture that classifies exceptional numbers. This conjecture
arises in two different ways, from cryptography and from coding theory. An odd
integer $t\geq 3$ is said to be exceptional if $f(x)=x^t$ is APN (Almost
Perfect Nonlinear) over $\mathbb{F}_{2^n}$ for infinitely many values of $n$.
Equivalently, $t$ is exceptional if the binary cyclic code of length $2^n-1$
with two zeros $\omega, \omega^t$ has minimum distance 5 for infinitely many
values of $n$. The conjecture we prove states that every exceptional number has
the form $2^i+1$ or $4^i-2^i+1$.
We consider exceptional APN functions on ${\bf F}_{2^m}$, which by definition
are functions that are not APN on infinitely many extensions of ${\bf
F}_{2^m}$. Our main result is that polynomial functions of odd degree are not
exceptional, provided the degree is not a Gold member ($2^k+1$) or a
Kasami-Welch number ($4^k-2^k+1$). We also have partial results on functions of
even degree, and functions that have degree $2^k+1$.