ABSTRACT
Denote by the class of locally integrable functions A(ξ) satisfying the estimate |A(ξ)|≤C(1+|ξ|)α.
(3.1.1)
Deflnition 3.1.1. A pseudodifferential operator (PDO) of class is an operator defined on functions by the formula
(3.1.2)
where is the Fourier transform of . The function A(ξ) is called the symbol of the operator A.
