1. :Some non-analytic-hypoelliptic sums of squares of vector fields,Bullction AMS (to appear)
2. 1990. Remarks on the breakdown of analyticity for đband Szeg ō kernels.Proceeding of Sendai conference on harmonic analysis, Lecture Notes in Math., 1 to appear
3. :Some non-analytic-hypoelliptic sums of squares of vector fields ,Bullction AMS (to appear) A class of hypoelliptic PDE admitting non-analytic solution preprint