Degenerate Sobolev Spaces and Regularity of Subelliptic Equations

In a recent paper [11], the authors proved both a rough analogue of the Feerman-Phong regularity theorem for smooth subelliptic self-adjoint operators, and a rough analogue of a special diagonal case of Hormander's theorem for sums of squares of smooth vector elds. For convenience, both of these rough theorems were stated using the classical notion o