From Gårding's cones to $p$-convex hypersurfaces

We consider cones discovered by Gårding in 1959. They play the fundamental role in the modern theory of fully nonlinear second-order partial differential equations. A new classification of symmetric matrices is presented based on the $m$-positiveness property. Such a classification establishes a new trend in geometry, generating a notion of $m$-convex hypersurfaces.