The Koszul property as a topological invariant and a measure of singularities

Abstract

Cassidy, Phan and Shelton associate to any regular cell complex X a quadratic K-algebra R(X). They give a combinatorial solution to the question of when this algebra is Koszul. The algebra R(X) is a combinatorial invariant but not a topological invariant. We show that nevertheless, the property that R(x) be Koszul is a topological invariant. In the process we establish some conditions on the types of local singular- ities that can occur in cell complexes X such that R(X) is Koszul, and more generally in cell complexes that are pure and connected by codimension one faces.