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Sous-ellipticité d’opérateurs intégro-différentiels vérifiant le principe du maximum. (Subellipticity of integro-differential operators satisfying the maximum principle). (French) Zbl 0742.35077
Sémin. Équ. Dériv. Partielles, Éc. Polytech., Cent. Math., Palaiseau 1990-1991, No.XXII, 10 p. (1991).
Summary: In this paper, we prove the ellipticity of pseudodifferential operators with non integer order and positive kernels not vanishing too much, and the subellipticity of operators $$P=\sum_ jX^*_ jX_ j$$ of order $$\leq 2$$ when there exists an elliptic commutator of the pseudodifferential operators $$X_ j$$.

##### MSC:
 35S05 Pseudodifferential operators as generalizations of partial differential operators 47G30 Pseudodifferential operators 35B50 Maximum principles in context of PDEs
##### Keywords:
ellipticity; subellipticity
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