Chapter deals with a subject that is basically a topic in nonharmonic Fourier series. A detailed discussion of biorthogonal systems and biorthogonal expansions connected with exponential polynomials are presented. Another principal object of study is the distribution ζ T defined in the last section. It can often serve as an example on the basis of which the sharpness in many theorems can be tested. In particular, the Lyubich problem on zeros of mean periodic functions on ℝ1 is solved using properties of ζ T .
KeywordsPeriodic Function Main Class Exponential Expansion Biorthogonal System Exponential Polynomial
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