On the Necessity of Logarithmic Estimates for Hypoellipticity

Timur Akhunov, Lyudmila Korobenko

This paper is focused on necessary conditions for hypoellipticity of an operator $L$ of the form $L=L_1(x)+g(x)L_2(y)$, where the operator $L_1$ is either elliptic or parabolic, $L…