Hypoellipticity for infinitely degenerate elliptic and parabolic operators of second order
Toshihiko Hoshiro · Kyoto journal of mathematics · 1988
Example 1.Let a be a positive constant and k be a positive integer.Theorem 1 and 2 show that the operator Furthermore, notice th a t 2 ,(e)/lel -o as (recall (2.2)).Then, multiply- ing the both sides of (2.6) by lie, we see that