Semigroup commutators under differences.
Nicholas Th. Varopoulos (1992)
Revista Matemática Iberoamericana
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Nicholas Th. Varopoulos (1992)
Revista Matemática Iberoamericana
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André Unterberger, Julianne Unterberger (1976)
Annales de l'institut Fourier
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The aim of this paper is to show how, in order to prove regularity theorems, Hölder estimates, i.e. estimates involving products of powers of different semi-norms, can be used as well as standard estimates, and may in some instances be casier to prove.
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.
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.
Lars Hörmander (1961)
Annales de l'institut Fourier
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On donne une condition suffisante pour l’hypoellipticité d’une équation différentielle à coefficients variables. La démonstration utilise une paramétrix construite par transformation de Fourier.
Frank Weber (1998)
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze
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Izabella Laba, Terence Tao (2001)
Revista Matemática Iberoamericana
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We prove an x-ray estimate in general dimension which is a stronger version of Wolff's Kakeya estimate [12]. This generalizes the estimate in [13], which dealt with the n = 3 case.