Analytic Hypoellipticity for a Class of Sums of Squares of Vector Fields with Non-Symplectic Characteristic Variety

Antonio Bove, Makhlouf Derridj, David S. Tartakoff

The recent example of Hanges: $P={\partial }_t^2+t^2{\Delta }_x+{\partial }_{\theta (x)}^2$ in $R^3$ is analytic hypoelliptic in the sense of germs but not in the strong sense in any neighborhoo…