1. [1] F. V. Atkinson, On second-order non-linear oscillations, Pacific J. Math., 5 (1955), 643-647.
2. [2] Š. Belohorec, Oscilatorické riešenia istej nelineárnej diferenciálnej rovnice druhého rádu, Mat. -Fyz. _??_asopis Sloven. Akad. Vied., 11 (1961), 250-255.
3. [3] R. E. Edwards, Functional Analysis: Theory and Applications, Holt, Rinehart and Winston, New York, 1965.
4. [4] Á. Elbert and T. Kusano, Oscillation and nonoscillation theorems for a class of second order quasilinear differential equations, Acta Math. Hungarica, 56 (1990), 325-336.
5. [5] J. I. Diaz, Nonlinear Partial Differential Equations and Free Boundaries, Vol. I, Elliptic Equations, Pitman, Boston-London-Melbourne, 1985.