An elementary proof of Fedi\uı's theorem and extensions

Abstract

We present an elementary, $L^2,$ proof of Fedi\uı's theorem on arbitrary (e.g., infinite order) degeneracy and extensions. In particular, the proof allows and shows $C^{\infty },$ Gevrey, and real analytic hypoellipticity, and allows the coefficents to depend on the remaining variable as well.

5pp