Finding the Standard Model of Particle Physics, A Combinatorial Problem
  We present a combinatorial problem which consists in finding irreducible Krajewski diagrams from finite geometries. This problem boils down to placing arrows into a quadratic array with some additional constrains. The Krajewski diagrams play a central role in the description of finite noncommutative geometries. They allow to localise the standard model of particle physics within the set of all Yang-Mills-Higgs models. 
Jan-H. Jureit, Christoph A. Stephan