MR2197538 Wakabayashi, Seiichiro Seiichiro WAKABAYASHI Local Solvability of Operators with Principal Symbol $\xi_1^2+\cdots+\xi_{n-1}^2+x_n^2\xi_n^2$ in the Spaces of Distributions and Ultradistributions Funkcialaj Ekvacioj. Serio Internacia 48 2005 453--487 http://fe.math.kobe-u.ac.jp/FE/FullPapers/48-3/48_453.pdf http://www.ams.org/mathscinet-getitem?mr=MR2197538 In this paper we shall illustrate how to study local solvability in the spaces of distributions and ultradistributions through the studies on operators of a special form. We shall give necessary conditions and sufficient conditions for these operators. Local solvability, Solvability in the spaces of distributions and ultradistribution. Primary 35A07; Secondary 35S05, 35B45. 48-453 2005 Local Solvability of Operators with Principal Symbol $\xi_1^2+\cdots+\xi_{n-1}^2+x_n^2\xi_n^2$ in the Spaces of Distributions and Ultradistributions WAKABAYASHI, Seiichiro Seiichiro WAKABAYASHI
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