On the structure of cellular pseudomanifolds

In this paper we study the structure of cellular pseudomanifolds (aka abstract polytopes). These are natural combinatorial generalisations of polytopal spheres (i.e., boundary complexes of convex polytopes). This class is closed under natural notions of duality and product. We show that they are also closed under an operation of direct product. Any cellular pseudomanifold and it's dual have homeomorphic geometric carriers, while the geometric carrier of the product of two of them is homeomorphic to the product of the carriers of the factors. The excess of a cellular pseudomanifold is defined as the non-negative integer $n - d - 2$ where $d$ is the dimension and $n$ is the number of vertices. We completely classify the cellular pseudo manifolds of excess $< 2$, and make some progress towards classifying those of excess 2.