Minimal digraph obstructions for small matrices

Abstract

Given a $\{0,1,\ast \}$-matrix $M$, a minimal $M$-obstruction is a digraph $D$ such that $D$ is not $M$-partitionable, but every proper induced subdigraph of $D$ is. In this note we present a list of all the $M$-obstructions for every $2\times 2$ matrix $M$. Notice that this note will be part of a larger paper, but we are archiving it now so we can cite the results.

9 pages, 2 figures