\Bibitem{KosOra75} \by A.~G.~Kostyuchenko, M.~B.~Orazov \paper Certain properties of the roots of a self-adjoint quadratic pencil \jour Funktsional. Anal. i Prilozhen. \yr 1975 \vol 9 \issue 4 \pages 28--40 \mathnet{http://mi.mathnet.ru/faa2279} \mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=0415375} \zmath{https://zbmath.org/?q=an:0356.47014} \transl \jour Funct. Anal. Appl. \yr 1975 \vol 9 \issue 4 \pages 295--305 \crossref{https://doi.org/10.1007/BF01075875}