Acta Mathematica · 1979 · 206 citations · 23 references
Natural SciencesMathematicsComputational GeometryBoundary ConditionsBoundary-value ProblemsPartial Differential EquationsElliptic Boundary-value ProblemsNeumann Problems
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Hypoelliptic second order differential equations
Lars Hörmander · Acta Mathematica · 1967 · 2.4K citations · Full text
Pseudo-differential Operators and Non-elliptic Boundary Problems
Lars Hörmander · Annals of Mathematics · 1966 · 496 citations