The Minimal Non-Koszul A(Gamma)
  The algebras $A(\Gamma)$, where $\Gamma$ is a directed layered graph, were first constructed by I. Gelfand, S. Serconek, V. Retakh and R. Wilson. These algebras are generalizations of the algebras $Q_n$, which are related to factorizations of non-commutative polynomials. It was conjectured that these algebras were Koszul. In 2008, T.Cassidy and B.Shelton found a counterexample to this claim, a non-Koszul $A(\Gamma)$ corresponding to a graph $\Gamma$ with 18 edges and 11 vertices.   We produce an example of a directed layered graph $\Gamma$ with 13 edges and 9 vertices which produces a non-Koszul $A(\Gamma)$. We also show this is the minimal example with this property. 
David Nacin
math.QA math.RA