The size of the smallest uniquely completable set in order 8 Latin squares

Abstract

In 1990, Kolesova, Lam and Thiel determined the 283,657 main classes of Latin squares of order 8. Using techniques to determine relevant Latin trades and integer programming, we examine representatives of each of these main classes and determine that none can contain a uniquely completable set of size less than 16. In three of these main classes, the use of trades which contain less than or equal to three rows, columns, or elements does not suffice to determine this fact. We closely examine properties of representatives of these three main classes. Writing the main result in Nelder's notation for critical sets, we prove that scs(8)=16.