2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/56587Discovered by M.G.Krein analogy between polinomials orthogonal on the unit circle and generalized eigenfunctions of certain differential systems is used to obtain some new results in the spectral analysis of Sturm-Liouville operators. Some properties of Dirac-type differential systems are studied.11 pages, LaTeXMathematical Physics34B24, 34L20text