[1] BLAŠKO R.: Contribution to higher monotonicity properties of certain Sturm-Liouville functions. Mathemat. Slovaca, to appear.

[2] BUTLEWSKI Z.: Sur les intégrales ďune équation différentielle du second ordre. Mathematica Cluj, 12, 1936, 36-48.

[3] HÁČIK M.: A note on higher monotonicity propeгties of ceгtain Sturm-Liouville functions. Archivum Mathematicum Brno, 3, 1980, 153-160.

[4] LORCH L., MULDOON M. E., SZEGO P.: Higher monotonicity propeгties of certain Sturm-Liouville functions IV. Canad. J. Math., 1972, 349-368. MR 0298113

[5] MAKAI E.: On a monotonic property of certain Sturm-Liouville functions. Acta Math. Acad. Sci. Hungar. 3, 1952, 165-172. MR 0054103 | Zbl 0048.32302

[6] SZEGO G.: Orthogonal polynomials. Amer. Math. Soc. Colloq. Publications 23, 3-rd edition, 1967.

[7] WATSON G. N.: A treatise on the theory of Bessel functioпs. 2-nd edition. Cambridge University Press, London, 1944. MR 0010746

[8] WILLETT D.: Classification of second order linear differential equations with respect to oscillation. Advances in Math., 3, No. 4, 1969, 594-623. MR 0280800 | Zbl 0188.40101

[9] WIMAN A.: Über eine Stabilitätsfrage in der Theorie der linearen Differentialgleichungen. Acta Math. 66, 1936, 121-145. MR 1555411 | Zbl 0014.01902