The characteristic 2 anisotropicity of simplicial spheres
Abstract
Assume D is a simplicial sphere, and k1 is a field. We say that D is generically anisotropic over k1 if, for a certain purely transcendental field extension k of k1, a certain Artinian reduction A of the Stanley-Reisner ring k[D] has the following property: All nonzero homogeneous elements u of A of degree less or equal to (dim D +1)/2 have nonzero square. We prove, using suitable differential operators, that, if the field k1 has characteristic 2, then every simplicial sphere D is generically anisotropic over k1. As an application, we give a second proof of a recent result of Adiprasito, known as McMullen's g-conjecture for simplicial spheres. We also prove that the simplicial spheres of dimension 1 are generically anisotropic over any field k1.