Abstract:
In this article we study conditions on the symbol of differential or pseudodifferential operators that characterize them as belonging to the class of subelliptic operators, the properties of which are close to those of elliptic operators. We give for the first time full proofs of the theorem about the equivalence of the algebraic conditions on the principal symbol and the conditions for subellipticity. Our results can be used in the study of boundary value problems for elliptic equations.
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