Sign regularity conditions for discontinuous boundary-value problems (Q869730)

For a multipoint discontinuous boundary-value problem with nonoscillating differential operator the author presents an analog of the Kalafati conditions that ensure the sign regularity property, i.e., the property that the number of sign changes of the solution does not exceed the number of sign changes of the function on the right-hand side. The sign regularity property allows one to verify whether the spectrum of the corresponding spectral problem exhibits the Sturm properties (i.e., the reality, positiveness, and simplicity of eigenvalues, the alternation of zeros of eigenfunctions, etc.).