1. Ahmad, Sh. and Lazer, A. C., On nth order Sturmian theory, J. Differential Equations 35 (1980), 87–112.
2. Ahmad, Sh. and Lazer, A. C., On an extension of the Sturm comparison Theorem, Siam J. Math. Anal., 12 (1981), 1–9.
3. Ananeva, G. B. and Balaganski, V. I., Oscillation of the solutions of certain differential equations of higher order, Uspekhi Mat. Nauk, 14(1959), 135140.
4. Atkinson, K. and Sharma, A., A partial characterization of poised Hermite-Birkhoff interpolation problems, SIAM J. Numer. Anal., 6 (1969), 230–235.
5. Bartusek, M., Properties of oscillating solutions of ordinary differential inequalities and equations, Differential Equations, 23 (1987), 129–132.