Necessary and sufficient conditions for the local solvability in hyperfunctions of a class of systems of complex vector fields.
A New Proof of Okaji’s Theorem for a Class of Sum of Squares Operators
Let be a linear partial differential operator with analytic coefficients. We assume that is of the form “sum of squares”, satisfying Hörmander’s bracket condition. Let be a characteristic point for . We assume that lies on a symplectic Poisson stratum of codimension two. General results of Okaji show that is analytic hypoelliptic at . Hence Okaji has established the validity of Treves’ conjecture in the codimension two case. Our goal here is to give a simple, self-contained proof of...
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