1. On second order nonlinear oscillations;Atkinson;Pacific J. Math.,1955
2. Oscillation of nonlinear second order equations;Bobisud,1969
3. Oscillation theorems for second order nonlinear differential equations;Erbe,1970
4. Ordinary Differential Equations;Hartman,1964
5. On oscillations of nonlinear equations of second order;Kartsatos;J. Math. Anal. Appl.,1968