Richard Beals (1979)
Annales de l'institut Fourier
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Continuity in spaces and spaces of Hölder type is proved for pseudodifferential operators of order zero, under general conditions on the class of symbols. Applications to the regularity theory of some hypoelliptic operators are outlined.
Charles L. Fefferman, Joseph J. Kohn (1988)
Revista Matemática Iberoamericana
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Anders Melin (1978)
Journées équations aux dérivées partielles
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Nicholas Th. Varopoulos (1993)
Revista Matemática Iberoamericana
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This is the second instalment of my previous paper with the same title, [1]. This paper consists of two different parts. The first part is devoted to improvements of the results developed in [1]. These improvements are described in section 0.1 below and developed in sections 1 to 5, and 9 to 10; they are in fact technically distinct from [1] and rely on a systematic use of microlocalisation in the context of Hörmander-Weyl calculus. These paragraphs can therefore be read quite independently...
Nicholas Th. Varopoulos (1992)
Revista Matemática Iberoamericana
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A. Menikoff (1977)
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze
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Antonio Sánchez-Calle (1988)
Revista Matemática Iberoamericana
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In this note we are going to address the question of when a second order differential operator is controlled by a subelliptic second order differential operator.