Determination of the Structure of the Spectrum of Regular Boundary Value Problems for Differential Equations by V.A. Il’in’s Method of Anti–A Priori Estimates

摘要

So far, there exists no example of a regular boundary value problem for differential equations with finite (but not empty) spectrum. In this paper, by using V.A. Il’in’s method of anti–a priori estimates, we show that the spectrum of differential operators generated by regular boundary conditions is either empty or infinite.