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Published online by Cambridge University Press: 22 January 2016
Let
(1) p(x,D)u = f
be a system of partial difierential equations. We shall say that p (x,D) is hypoelliptic if the distribution solution u is in C∞ wherever f∈C∞ (cf. section 2, Definition 5.)
Here we shall give a sufficient condition for the hypoellipticity of overdetermined systems with variable coefficients.